转自:http://blog.csdn.net/jmq_0000/article/details/7536805#t136
Video for Linux Two API Specification
Revision 0.24
Michael H Schimek
Bill Dirks
Hans Verkuil
Martin Rubli
Copyright © 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008 Bill Dirks, Michael H. Schimek, Hans Verkuil, MartinRubli
This document is copyrighted © 1999-2008 by BillDirks, Michael H. Schimek, Hans Verkuil and Martin Rubli.
Permission is granted to copy, distribute and/or modifythis document under the terms of the GNU Free Documentation License,Version 1.1 or any later version published by the Free SoftwareFoundation; with no Invariant Sections, with no Front-Cover Texts, andwith no Back-Cover Texts. A copy of the license is included in theappendix entitled "GNU Free Documentation License".
Programming examples can be used and distributed withoutrestrictions.
- Table of Contents
Introduction
- 1. Common API Elements
-
- 1.1. Opening and Closing Devices
-
- 1.1.1. Device Naming
- 1.1.2. Related Devices
- 1.1.3. Multiple Opens
- 1.1.4. Shared Data Streams
- 1.1.5. Functions
- 1.2. Querying Capabilities
- 1.3. Application Priority
- 1.4. Video Inputs and Outputs
- 1.5. Audio Inputs and Outputs
- 1.6. Tuners and Modulators
-
- 1.6.1. Tuners
- 1.6.2. Modulators
- 1.6.3. Radio Frequency
- 1.6.4. Satellite Receivers
- 1.7. Video Standards
- 1.8. User Controls
- 1.9. Extended Controls
-
- 1.9.1. Introduction
- 1.9.2. The Extended Control API
- 1.9.3. Enumerating Extended Controls
- 1.9.4. Creating Control Panels
- 1.9.5. MPEG Control Reference
- 1.9.6. Camera Control Reference
- 1.10. Data Formats
-
- 1.10.1. Data Format Negotiation
- 1.10.2. Image Format Enumeration
- 1.11. Image Cropping, Insertion and Scaling
-
- 1.11.1. Cropping Structures
- 1.11.2. Scaling Adjustments
- 1.11.3. Examples
- 1.12. Streaming Parameters
- 2. Image Formats
-
- 2.1. Standard Image Formats
- 2.2. Colorspaces
- 2.3. Indexed Format
- 2.4. RGB Formats
-
- Packed RGB formats -- Packed RGB formats
- V4L2_PIX_FMT_SBGGR8 ('BA81') -- Bayer RGB format
- V4L2_PIX_FMT_SBGGR16 ('BA82') -- Bayer RGB format
- 2.5. YUV Formats
-
- Packed YUV formats -- Packed YUV formats
- V4L2_PIX_FMT_GREY ('GREY') -- Grey-scale image
- V4L2_PIX_FMT_Y16 ('Y16 ') -- Grey-scale image
- V4L2_PIX_FMT_YUYV ('YUYV') -- Packed format with ½ horizontal chromaresolution, also known as YUV 4:2:2
-
V4L2_PIX_FMT_UYVY ('UYVY') -- Variation of
V4L2_PIX_FMT_YUYV
with different order of samplesin memory - V4L2_PIX_FMT_Y41P ('Y41P') -- Format with ¼ horizontal chromaresolution, also known as YUV 4:1:1
- V4L2_PIX_FMT_YVU420 ('YV12'), V4L2_PIX_FMT_YUV420 ('YU12') -- Planar formats with ½ horizontal andvertical chroma resolution, also known as YUV 4:2:0
- V4L2_PIX_FMT_YVU410 ('YVU9'), V4L2_PIX_FMT_YUV410 ('YUV9') -- Planar formats with ¼ horizontal andvertical chroma resolution, also known as YUV 4:1:0
-
V4L2_PIX_FMT_YUV422P ('422P') -- Format with ½ horizontal chroma resolution,also known as YUV 4:2:2. Planar layout as opposed to
V4L2_PIX_FMT_YUYV
-
V4L2_PIX_FMT_YUV411P ('411P') -- Format with ¼ horizontal chroma resolution,also known as YUV 4:1:1. Planar layout as opposed to
V4L2_PIX_FMT_Y41P
-
V4L2_PIX_FMT_NV12 ('NV12'), V4L2_PIX_FMT_NV21 ('NV21') -- Formats with ½ horizontal and verticalchroma resolution, also known as YUV 4:2:0. One luminance and onechrominance plane with alternating chroma samples as opposed to
V4L2_PIX_FMT_YVU420
- 2.6. Compressed Formats
- 2.7. Reserved Format Identifiers
- 3. Input/Output
-
- 3.1. Read/Write
- 3.2. Streaming I/O (Memory Mapping)
- 3.3. Streaming I/O (User Pointers)
- 3.4. Asynchronous I/O
- 3.5. Buffers
-
- 3.5.1. Timecodes
- 3.6. Field Order
- 4. Interfaces
-
- 4.1. Video Capture Interface
-
- 4.1.1. Querying Capabilities
- 4.1.2. Supplemental Functions
- 4.1.3. Image Format Negotiation
- 4.1.4. Reading Images
- 4.2. Video Overlay Interface
-
- 4.2.1. Querying Capabilities
- 4.2.2. Supplemental Functions
- 4.2.3. Setup
- 4.2.4. Overlay Window
- 4.2.5. Enabling Overlay
- 4.3. Video Output Interface
-
- 4.3.1. Querying Capabilities
- 4.3.2. Supplemental Functions
- 4.3.3. Image Format Negotiation
- 4.3.4. Writing Images
- 4.4. Video Output Overlay Interface
-
- 4.4.1. Querying Capabilities
- 4.4.2. Framebuffer
- 4.4.3. Overlay Window and Scaling
- 4.4.4. Enabling Overlay
- 4.5. Codec Interface
- 4.6. Effect Devices Interface
- 4.7. Raw VBI Data Interface
-
- 4.7.1. Querying Capabilities
- 4.7.2. Supplemental Functions
- 4.7.3. Raw VBI Format Negotiation
- 4.7.4. Reading and writing VBI images
- 4.8. Sliced VBI Data Interface
-
- 4.8.1. Querying Capabilities
- 4.8.2. Supplemental Functions
- 4.8.3. Sliced VBI Format Negotiation
- 4.8.4. Reading and writing sliced VBI data
- 4.9. Teletext Interface
- 4.10. Radio Interface
-
- 4.10.1. Querying Capabilities
- 4.10.2. Supplemental Functions
- 4.10.3. Programming
- 4.11. RDS Interface
- I. Function Reference
-
- V4L2 close() -- Close a V4L2 device
- V4L2 ioctl() -- Program a V4L2 device
- ioctl VIDIOC_CROPCAP -- Information about the video cropping and scaling abilities
- ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER -- Read or write hardware registers
- ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD -- Execute an encoder command
- ioctl VIDIOC_ENUMAUDIO -- Enumerate audio inputs
- ioctl VIDIOC_ENUMAUDOUT -- Enumerate audio outputs
- ioctl VIDIOC_ENUM_FMT -- Enumerate image formats
- ioctl VIDIOC_ENUM_FRAMESIZES -- Enumerate frame sizes
- ioctl VIDIOC_ENUM_FRAMEINTERVALS -- Enumerate frame intervals
- ioctl VIDIOC_ENUMINPUT -- Enumerate video inputs
- ioctl VIDIOC_ENUMOUTPUT -- Enumerate video outputs
- ioctl VIDIOC_ENUMSTD -- Enumerate supported video standards
- ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO -- Query or select the current audio input and itsattributes
- ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT -- Query or select the current audio output
- ioctl VIDIOC_G_CHIP_IDENT -- Identify the chips on a TV card
- ioctl VIDIOC_G_CROP, VIDIOC_S_CROP -- Get or set the current cropping rectangle
- ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL -- Get or set the value of a control
- ioctl VIDIOC_G_ENC_INDEX -- Get meta data about a compressed video stream
- ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,VIDIOC_TRY_EXT_CTRLS -- Get or set the value of several controls, try controlvalues
- ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF -- Get or set frame buffer overlay parameters
- ioctl VIDIOC_G_FMT, VIDIOC_S_FMT,VIDIOC_TRY_FMT -- Get or set the data format, try a format
- ioctl VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY -- Get or set tuner or modulator radiofrequency
- ioctl VIDIOC_G_INPUT, VIDIOC_S_INPUT -- Query or select the current video input
- ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP --
- ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR -- Get or set modulator attributes
- ioctl VIDIOC_G_OUTPUT, VIDIOC_S_OUTPUT -- Query or select the current video output
- ioctl VIDIOC_G_PARM, VIDIOC_S_PARM -- Get or set streaming parameters
- ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY -- Query or request the access priority associated with afile descriptor
- ioctl VIDIOC_G_SLICED_VBI_CAP -- Query sliced VBI capabilities
- ioctl VIDIOC_G_STD, VIDIOC_S_STD -- Query or select the video standard of the current input
- ioctl VIDIOC_G_TUNER, VIDIOC_S_TUNER -- Get or set tuner attributes
- ioctl VIDIOC_LOG_STATUS -- Log driver status information
- ioctl VIDIOC_OVERLAY -- Start or stop video overlay
- ioctl VIDIOC_QBUF, VIDIOC_DQBUF -- Exchange a buffer with the driver
- ioctl VIDIOC_QUERYBUF -- Query the status of a buffer
- ioctl VIDIOC_QUERYCAP -- Query device capabilities
- ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU -- Enumerate controls and menu control items
- ioctl VIDIOC_QUERYSTD -- Sense the video standard received by the currentinput
- ioctl VIDIOC_REQBUFS -- Initiate Memory Mapping or User Pointer I/O
- ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF -- Start or stop streaming I/O
- V4L2 mmap() -- Map device memory into application address space
- V4L2 munmap() -- Unmap device memory
- V4L2 open() -- Open a V4L2 device
- V4L2 poll() -- Wait for some event on a file descriptor
- V4L2 read() -- Read from a V4L2 device
- V4L2 select() -- Synchronous I/O multiplexing
- V4L2 write() -- Write to a V4L2 device
- 5. V4L2 Driver Programming
- 6. Changes
-
- 6.1. Differences between V4L and V4L2
-
- 6.1.1. Opening and Closing Devices
- 6.1.2. Querying Capabilities
- 6.1.3. Video Sources
- 6.1.4. Tuning
- 6.1.5. Image Properties
- 6.1.6. Audio
- 6.1.7. Frame Buffer Overlay
- 6.1.8. Cropping
- 6.1.9. Reading Images, Memory Mapping
- 6.1.10. Reading Raw VBI Data
- 6.1.11. Miscellaneous
- 6.2. Changes of the V4L2 API
-
- 6.2.1. Early Versions
- 6.2.2. V4L2 Version 0.16 1999-01-31
- 6.2.3. V4L2 Version 0.18 1999-03-16
- 6.2.4. V4L2 Version 0.19 1999-06-05
- 6.2.5. V4L2 Version 0.20 (1999-09-10)
- 6.2.6. V4L2 Version 0.20 incremental changes
- 6.2.7. V4L2 Version 0.20 2000-11-23
- 6.2.8. V4L2 Version 0.20 2002-07-25
- 6.2.9. V4L2 in Linux 2.5.46, 2002-10
- 6.2.10. V4L2 2003-06-19
- 6.2.11. V4L2 2003-11-05
- 6.2.12. V4L2 in Linux 2.6.6, 2004-05-09
- 6.2.13. V4L2 in Linux 2.6.8
- 6.2.14. V4L2 spec erratum 2004-08-01
- 6.2.15. V4L2 in Linux 2.6.14
- 6.2.16. V4L2 in Linux 2.6.15
- 6.2.17. V4L2 spec erratum 2005-11-27
- 6.2.18. V4L2 spec erratum 2006-01-10
- 6.2.19. V4L2 spec erratum 2006-02-03
- 6.2.20. V4L2 spec erratum 2006-02-04
- 6.2.21. V4L2 in Linux 2.6.17
- 6.2.22. V4L2 spec erratum 2006-09-23 (Draft 0.15)
- 6.2.23. V4L2 in Linux 2.6.18
- 6.2.24. V4L2 in Linux 2.6.19
- 6.2.25. V4L2 spec erratum 2006-10-12 (Draft 0.17)
- 6.2.26. V4L2 in Linux 2.6.21
- 6.2.27. V4L2 in Linux 2.6.22
- 6.2.28. V4L2 in Linux 2.6.24
- 6.2.29. V4L2 in Linux 2.6.25
- 6.3. Relation of V4L2 to other Linux multimedia APIs
-
- 6.3.1. X Video Extension
- 6.3.2. Digital Video
- 6.3.3. Audio Interfaces
- 6.4. Experimental API Elements
- 6.5. Obsolete API Elements
- A. Video For Linux Two Header File
- B. Video Capture Example
- C. GNU Free Documentation License
-
- C.1. 0. PREAMBLE
- C.2. 1. APPLICABILITY AND DEFINITIONS
- C.3. 2. VERBATIM COPYING
- C.4. 3. COPYING IN QUANTITY
- C.5. 4. MODIFICATIONS
- C.6. 5. COMBINING DOCUMENTS
- C.7. 6. COLLECTIONS OF DOCUMENTS
- C.8. 7. AGGREGATION WITH INDEPENDENT WORKS
- C.9. 8. TRANSLATION
- C.10. 9. TERMINATION
- C.11. 10. FUTURE REVISIONS OF THIS LICENSE
- C.12. Addendum
- List of Types
- References
- List of Examples
- 1-1. Information about the current video input
- 1-2. Switching to the first video input
- 1-3. Information about the current audio input
- 1-4. Switching to the first audio input
- 1-5. Information about the current video standard
- 1-6. Listing the video standards supported by the currentinput
- 1-7. Selecting a new video standard
- 1-8. Enumerating all controls
- 1-9. Changing controls
- 1-10. Resetting the cropping parameters
- 1-11. Simple downscaling
- 1-12. Selecting an output area
- 1-13. Current scaling factor and pixel aspect
- 2-1. ITU-R Rec. BT.601 color conversion
-
2-1.
V4L2_PIX_FMT_BGR24
4 × 4 pixelimage -
2-1.
V4L2_PIX_FMT_SBGGR8
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_SBGGR16
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_GREY
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_Y16
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_YUYV
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_UYVY
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_Y41P
8 × 4pixel image -
2-1.
V4L2_PIX_FMT_YVU420
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_YVU410
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_YUV422P
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_YUV411P
4 × 4pixel image -
2-1.
V4L2_PIX_FMT_NV12
4 × 4pixel image - 3-1. Mapping buffers
- 3-2. Initiating streaming I/O with user pointers
- 4-1. Finding a framebuffer device for OSD
Introduction
Video For Linux Two is the second version of the Video ForLinux API, a kernel interface for analog radio and video capture andoutput drivers.
Early drivers used ad-hoc interfaces. These were replaced inLinux 2.2 by Alan Cox' V4L API, based on the interface of the bttvdriver. In 1999 Bill Dirks started the development of V4L2 to fix someshortcomings of V4L and to support a wider range of devices. The APIwas revised again in 2002 prior to its inclusion in Linux 2.5/2.6, andwork continues on improvements and additions while maintainingcompatibility with existing drivers and applications. In 2006/2007efforts began on FreeBSD drivers with a V4L2 interface.
This book documents the V4L2 API. Intended audience aredriver and application writers.
If you have questions or ideas regarding the API, pleasewrite to the Video4Linux mailing list:https://listman.redhat.com/mailman/listinfo/video4linux-list. For inquiries aboutthe V4L2 specification contact the maintainermschimek@gmx.at.
The latest version of this document and the DocBook SGMLsources are hosted at http://v4l2spec.bytesex.org,and http://linuxtv.org/downloads/video4linux/API/V4L2_API.
Chapter 1. Common API Elements
Programming a V4L2 device consists of thesesteps:
-
Opening the device
-
Changing device properties, selecting a video and audioinput, video standard, picture brightness a. o.
-
Negotiating a data format
-
Negotiating an input/output method
-
The actual input/output loop
-
Closing the device
In practice most steps are optional and can be executed out oforder. It depends on the V4L2 device type, you can read about thedetails inChapter 4. In this chapter we will discussthe basic concepts applicable to all devices.
1.1. Opening and Closing Devices
1.1.1. Device Naming
V4L2 drivers are implemented as kernel modules, loadedmanually by the system administrator or automatically when a device isfirst opened. The driver modules plug into the "videodev" kernelmodule. It provides helper functions and a common applicationinterface specified in this document.
Each driver thus loaded registers one or more device nodeswith major number 81 and a minor number between 0 and 255. Assigningminor numbers to V4L2 devices is entirely up to the system administrator,this is primarily intended to solve conflicts between devices.[1] The module options to select minor numbers are namedafter the device special file with a "_nr" suffix. For example "video_nr"for/dev/video video capture devices. The number isan offset to the base minor number associated with the device type.[2] When the driver supports multiple devices of the sametype more than one minor number can be assigned, separated by commas:
In /etc/modules.conf this may bewritten as:
alias char-major-81-0 mydriver alias char-major-81-1 mydriver alias char-major-81-64 mydriver
options mydriver video_nr=0,1 radio_nr=0,1
- When an application attempts to open a devicespecial file with major number 81 and minor number 0, 1, or 64, load"mydriver" (and the "videodev" module it depends upon).
- Register the first two video capture devices withminor number 0 and 1 (base number is 0), the first two radio devicewith minor number 64 and 65 (base 64).
By convention system administrators create variouscharacter device special files with these major and minor numbers inthe/dev directory. The names recomended for thedifferent V4L2 device types are listed inChapter 4.
The creation of character special files (withmknod) is a privileged operation anddevices cannot be opened by major and minor number. That meansapplications cannotreliable scan for loaded orinstalled drivers. The user must enter a device name, or theapplication can try the conventional device names.
Under the device filesystem (devfs) the minor numberoptions are ignored. V4L2 drivers (or by proxy the "videodev" module)automatically create the required device files in the/dev/v4l directory using the conventional devicenames above.
1.1.2. Related Devices
Devices can support several related functions. For examplevideo capturing, video overlay and VBI capturing are related becausethese functions share, amongst other, the same video input and tunerfrequency. V4L and earlier versions of V4L2 used the same device nameand minor number for video capturing and overlay, but different onesfor VBI. Experience showed this approach has several problems[3], and to make things worse the V4L videodev moduleused to prohibit multiple opens of a device.
As a remedy the present version of the V4L2 API relaxed theconcept of device types with specific names and minor numbers. Forcompatibility with old applications drivers must still register differentminor numbers to assign a default function to the device. But if relatedfunctions are supported by the driver they must be available under allregistered minor numbers. The desired function can be selected afteropening the device as described inChapter 4.
Imagine a driver supporting video capturing, videooverlay, raw VBI capturing, and FM radio reception. It registers threedevices with minor number 0, 64 and 224 (this numbering scheme isinherited from the V4L API). Regardless if/dev/video (81, 0) or/dev/vbi (81, 224) is opened the application canselect any one of the video capturing, overlay or VBI capturingfunctions. Without programming (e. g. reading from the devicewithdd orcat)/dev/video captures video images, while/dev/vbi captures raw VBI data./dev/radio (81, 64) is invariable a radio device,unrelated to the video functions. Being unrelated does not imply thedevices can be used at the same time, however. Theopen()
function may very well return anEBUSY error code.
Besides video input or output the hardware may alsosupport audio sampling or playback. If so, these functions areimplemented as OSS or ALSA PCM devices and eventually OSS or ALSAaudio mixer. The V4L2 API makes no provisions yet to find theserelated devices. If you have an idea please write to the Video4Linuxmailing list: https://listman.redhat.com/mailman/listinfo/video4linux-list.
1.1.3. Multiple Opens
In general, V4L2 devices can be opened more than once.When this is supported by the driver, users can for example start a"panel" application to change controls like brightness or audiovolume, while another application captures video and audio. In other words, panelapplications are comparable to an OSS or ALSA audio mixer application.When a device supports multiple functions like capturing and overlaysimultaneously, multiple opens allow concurrentuse of the device by forked processes or specialized applications.
Multiple opens are optional, although drivers shouldpermit at least concurrent accesses without data exchange, i. e. panelapplications. This impliesopen()
can return anEBUSY error code when thedevice is already in use, as well asioctl()
functions initiatingdata exchange (namely theVIDIOC_S_FMT
ioctl), and theread()
andwrite()
functions.
Mere opening a V4L2 device does not grant exclusiveaccess.[4] Initiating data exchange however assigns the rightto read or write the requested type of data, and to change relatedproperties, to this file descriptor. Applications can requestadditional access privileges using the priority mechanism described inSection 1.3.
1.1.4. Shared Data Streams
V4L2 drivers should not support multiple applicationsreading or writing the same data stream on a device by copyingbuffers, time multiplexing or similar means. This is better handled bya proxy application in user space. When the driver supports streamsharing anyway it must be implemented transparently. The V4L2 API doesnot specify how conflicts are solved.
1.2. Querying Capabilities
Because V4L2 covers a wide variety of devices not allaspects of the API are equally applicable to all types of devices.Furthermore devices of the same type have different capabilities andthis specification permits the omission of a few complicated and lessimportant parts of the API.
The VIDIOC_QUERYCAP
ioctl is available to check if the kerneldevice is compatible with this specification, and to query thefunctions andI/Omethods supported by the device. Other features can be queriedby calling the respective ioctl, for exampleVIDIOC_ENUMINPUT
to learn about the number, types and names of video connectors on thedevice. Although abstraction is a major objective of this API, theioctl also allows driver specific applications to reliable identifythe driver.
All V4L2 drivers must supportVIDIOC_QUERYCAP
. Applications should always callthis ioctl after opening the device.
1.3. Application Priority
When multiple applications share a device it may bedesirable to assign them different priorities. Contrary to thetraditional "rm -rf /" school of thought a video recording applicationcould for example block other applications from changing videocontrols or switching the current TV channel. Another objective is topermit low priority applications working in background, which can bepreempted by user controlled applications and automatically regaincontrol of the device at a later time.
Since these features cannot be implemented entirely in userspace V4L2 defines theVIDIOC_G_PRIORITY
andVIDIOC_S_PRIORITY
ioctls to request and query the access priority associate with a filedescriptor. Opening a device assigns a medium priority, compatiblewith earlier versions of V4L2 and drivers not supporting these ioctls.Applications requiring a different priority will usually callVIDIOC_S_PRIORITY
after verifying the device withtheVIDIOC_QUERYCAP
ioctl.
Ioctls changing driver properties, such as VIDIOC_S_INPUT
,return an EBUSY error code after another application obtained higher priority.An event mechanism to notify applications about asynchronous propertychanges has been proposed but not added yet.
1.4. Video Inputs and Outputs
Video inputs and outputs are physical connectors of adevice. These can be for example RF connectors (antenna/cable), CVBSa.k.a. Composite Video, S-Video or RGB connectors. Only video and VBIcapture devices have inputs, output devices have outputs, at least oneeach. Radio devices have no video inputs or outputs.
To learn about the number and attributes of theavailable inputs and outputs applications can enumerate them with theVIDIOC_ENUMINPUT
andVIDIOC_ENUMOUTPUT
ioctl, respectively. Thestruct v4l2_input returned by theVIDIOC_ENUMINPUT
ioctl also contains signal status information applicable when thecurrent video input is queried.
The VIDIOC_G_INPUT
and VIDIOC_G_OUTPUT
ioctl return theindex of the current video input or output. To select a differentinput or output applications call theVIDIOC_S_INPUT
andVIDIOC_S_OUTPUT
ioctl. Drivers must implement all the input ioctlswhen the device has one or more inputs, all the output ioctls when thedevice has one or more outputs.
Example 1-1. Information about the current video input
struct v4l2_input input; int index; if (-1 == ioctl (fd,VIDIOC_G_INPUT
, &index)) { perror ("VIDIOC_G_INPUT"); exit (EXIT_FAILURE); } memset (&input, 0, sizeof (input)); input.index = index; if (-1 == ioctl (fd,VIDIOC_ENUMINPUT
, &input)) { perror ("VIDIOC_ENUMINPUT"); exit (EXIT_FAILURE); } printf ("Current input: %s\n", input.name);
Example 1-2. Switching to the first video input
int index;
index = 0;
if (-1 == ioctl (fd, VIDIOC_S_INPUT
, &index)) {
perror ("VIDIOC_S_INPUT");
exit (EXIT_FAILURE);
}
1.5. Audio Inputs and Outputs
Audio inputs and outputs are physical connectors of adevice. Video capture devices have inputs, output devices haveoutputs, zero or more each. Radio devices have no audio inputs oroutputs. They have exactly one tuner which in factis an audio source, but this API associatestuners with video inputs or outputs only, and radio devices havenone of these.[5] A connector on a TV card to loop back the receivedaudio signal to a sound card is not considered an audio output.
Audio and video inputs and outputs are associated. Selectinga video source also selects an audio source. This is most evident whenthe video and audio source is a tuner. Further audio connectors cancombine with more than one video input or output. Assumed twocomposite video inputs and two audio inputs exist, there may be up tofour valid combinations. The relation of video and audio connectorsis defined in theaudioset
field of therespective struct v4l2_input or struct v4l2_output, where each bit representsthe index number, starting at zero, of one audio input or output.
To learn about the number and attributes of theavailable inputs and outputs applications can enumerate them with theVIDIOC_ENUMAUDIO
andVIDIOC_ENUMAUDOUT
ioctl, respectively. Thestruct v4l2_audio returned by theVIDIOC_ENUMAUDIO
ioctlalso contains signal status information applicable when the currentaudio input is queried.
The VIDIOC_G_AUDIO
and VIDIOC_G_AUDOUT
ioctl reportthe current audio input and output, respectively. Note that, unlikeVIDIOC_G_INPUT
andVIDIOC_G_OUTPUT
these ioctls return a structureasVIDIOC_ENUMAUDIO
andVIDIOC_ENUMAUDOUT
do, not just an index.
To select an audio input and change its propertiesapplications call the VIDIOC_S_AUDIO
ioctl. To select an audiooutput (which presently has no changeable properties) applicationscall theVIDIOC_S_AUDOUT
ioctl.
Drivers must implement all input ioctls when the devicehas one or more inputs, all output ioctls when the device has oneor more outputs. When the device has any audio inputs or outputs thedriver must set theV4L2_CAP_AUDIO
flag in thestruct v4l2_capability returned by theVIDIOC_QUERYCAP
ioctl.
Example 1-3. Information about the current audio input
struct v4l2_audio audio;
memset (&audio, 0, sizeof (audio));
if (-1 == ioctl (fd, VIDIOC_G_AUDIO
, &audio)) {
perror ("VIDIOC_G_AUDIO");
exit (EXIT_FAILURE);
}
printf ("Current input: %s\n", audio.name);
Example 1-4. Switching to the first audio input
struct v4l2_audio audio;
memset (&audio, 0, sizeof (audio)); /* clear audio.mode, audio.reserved */
audio.index = 0;
if (-1 == ioctl (fd, VIDIOC_S_AUDIO
, &audio)) {
perror ("VIDIOC_S_AUDIO");
exit (EXIT_FAILURE);
}
1.6. Tuners and Modulators
1.6.1. Tuners
Video input devices can have one or more tunersdemodulating a RF signal. Each tuner is associated with one or morevideo inputs, depending on the number of RF connectors on the tuner.Thetype
field of the respectivestruct v4l2_input returned by theVIDIOC_ENUMINPUT
ioctl is set toV4L2_INPUT_TYPE_TUNER
and itstuner
field contains the index number ofthe tuner.
Radio devices have exactly one tuner with index zero, novideo inputs.
To query and change tuner properties applications use theVIDIOC_G_TUNER
andVIDIOC_S_TUNER
ioctl, respectively. Thestruct v4l2_tuner returned byVIDIOC_G_TUNER
alsocontains signal status information applicable when the tuner of thecurrent video input, or a radio tuner is queried. Note thatVIDIOC_S_TUNER
does not switch the current tuner,when there is more than one at all. The tuner is solely determined bythe current video input. Drivers must support both ioctls and set theV4L2_CAP_TUNER
flag in the struct v4l2_capabilityreturned by theVIDIOC_QUERYCAP
ioctl when the device has one ormore tuners.
1.6.2. Modulators
Video output devices can have one or more modulators, uh,modulating a video signal for radiation or connection to the antennainput of a TV set or video recorder. Each modulator is associated withone or more video outputs, depending on the number of RF connectors onthe modulator. The type
field of therespective struct v4l2_output returned by theVIDIOC_ENUMOUTPUT
ioctl isset toV4L2_OUTPUT_TYPE_MODULATOR
and itsmodulator
field contains the index numberof the modulator. This specification does not define radio outputdevices.
To query and change modulator properties applications usethe VIDIOC_G_MODULATOR
and VIDIOC_S_MODULATOR
ioctl. Note thatVIDIOC_S_MODULATOR
does not switch the currentmodulator, when there is more than one at all. The modulator is solelydetermined by the current video output. Drivers must support bothioctls and set the V4L2_CAP_TUNER
(sic) flag inthe struct v4l2_capability returned by theVIDIOC_QUERYCAP
ioctl when thedevice has one or more modulators.
1.6.3. Radio Frequency
To get and set the tuner or modulator radio frequencyapplications use the VIDIOC_G_FREQUENCY
and VIDIOC_S_FREQUENCY
ioctl which both take a pointer to a struct v4l2_frequency. These ioctlsare used for TV and radio devices alike. Drivers must support bothioctls when the tuner or modulator ioctls are supported, orwhen the device is a radio device.
1.7. Video Standards
Video devices typically support one or more different videostandards or variations of standards. Each video input and output maysupport another set of standards. This set is reported by thestd
field of struct v4l2_input andstruct v4l2_output returned by theVIDIOC_ENUMINPUT
andVIDIOC_ENUMOUTPUT
ioctl, respectively.
V4L2 defines one bit for each analog video standardcurrently in use worldwide, and sets aside bits for driver definedstandards, e. g. hybrid standards to watch NTSC video tapes on PAL TVsand vice versa. Applications can use the predefined bits to select aparticular standard, although presenting the user a menu of supportedstandards is preferred. To enumerate and query the attributes of thesupported standards applications use theVIDIOC_ENUMSTD
ioctl.
Many of the defined standards are actually just variationsof a few major standards. The hardware may in fact not distinguishbetween them, or do so internal and switch automatically. Thereforeenumerated standards also contain sets of one or more standardbits.
Assume a hypothetic tuner capable of demodulating B/PAL,G/PAL and I/PAL signals. The first enumerated standard is a set of Band G/PAL, switched automatically depending on the selected radiofrequency in UHF or VHF band. Enumeration gives a "PAL-B/G" or "PAL-I"choice. Similar a Composite input may collapse standards, enumerating"PAL-B/G/H/I", "NTSC-M" and "SECAM-D/K".[6]
To query and select the standard used by the current videoinput or output applications call theVIDIOC_G_STD
andVIDIOC_S_STD
ioctl, respectively. The receivedstandard can be sensed with theVIDIOC_QUERYSTD
ioctl. Note parameter of all these ioctls is a pointer to av4l2_std_id type (a standard set),not an index into the standard enumeration.[7] Drivers must implement all video standard ioctlswhen the device has one or more video inputs or outputs.
Special rules apply to USB cameras where the notion of videostandards makes little sense. More generally any capture device,output devices accordingly, which is
-
incapable of capturing fields or frames at the nominalrate of the video standard, or
-
where timestamps referto the instant the field or frame was received by the driver, not thecapture time, or
-
where sequence numbersrefer to the frames received by the driver, not the capturedframes.
std
field of struct
v4l2_input and struct
v4l2_outputto zero, the
VIDIOC_G_STD
,
VIDIOC_S_STD
,
VIDIOC_QUERYSTD
and
VIDIOC_ENUMSTD
ioctls shall return the
EINVAL error code.[8]
Example 1-5. Information about the current video standard
v4l2_std_id std_id; struct v4l2_standard standard; if (-1 == ioctl (fd,VIDIOC_G_STD
, &std_id)) { /* Note when VIDIOC_ENUMSTD always returns EINVAL this is no video device or it falls under the USB exception, and VIDIOC_G_STD returning EINVAL is no error. */ perror ("VIDIOC_G_STD"); exit (EXIT_FAILURE); } memset (&standard, 0, sizeof (standard)); standard.index = 0; while (0 == ioctl (fd,VIDIOC_ENUMSTD
, &standard)) { if (standard.id & std_id) { printf ("Current video standard: %s\n", standard.name); exit (EXIT_SUCCESS); } standard.index++; } /* EINVAL indicates the end of the enumeration, which cannot be empty unless this device falls under the USB exception. */ if (errno == EINVAL || standard.index == 0) { perror ("VIDIOC_ENUMSTD"); exit (EXIT_FAILURE); }
Example 1-6. Listing the video standards supported by the currentinput
struct v4l2_input input; struct v4l2_standard standard; memset (&input, 0, sizeof (input)); if (-1 == ioctl (fd,VIDIOC_G_INPUT
, &input.index)) { perror ("VIDIOC_G_INPUT"); exit (EXIT_FAILURE); } if (-1 == ioctl (fd,VIDIOC_ENUMINPUT
, &input)) { perror ("VIDIOC_ENUM_INPUT"); exit (EXIT_FAILURE); } printf ("Current input %s supports:\n", input.name); memset (&standard, 0, sizeof (standard)); standard.index = 0; while (0 == ioctl (fd,VIDIOC_ENUMSTD
, &standard)) { if (standard.id & input.std) printf ("%s\n", standard.name); standard.index++; } /* EINVAL indicates the end of the enumeration, which cannot be empty unless this device falls under the USB exception. */ if (errno != EINVAL || standard.index == 0) { perror ("VIDIOC_ENUMSTD"); exit (EXIT_FAILURE); }
Example 1-7. Selecting a new video standard
struct v4l2_input input; v4l2_std_id std_id; memset (&input, 0, sizeof (input)); if (-1 == ioctl (fd,VIDIOC_G_INPUT
, &input.index)) { perror ("VIDIOC_G_INPUT"); exit (EXIT_FAILURE); } if (-1 == ioctl (fd,VIDIOC_ENUMINPUT
, &input)) { perror ("VIDIOC_ENUM_INPUT"); exit (EXIT_FAILURE); } if (0 == (input.std & V4L2_STD_PAL_BG)) { fprintf (stderr, "Oops. B/G PAL is not supported.\n"); exit (EXIT_FAILURE); } /* Note this is also supposed to work when only B or G/PAL is supported. */ std_id = V4L2_STD_PAL_BG; if (-1 == ioctl (fd,VIDIOC_S_STD
, &std_id)) { perror ("VIDIOC_S_STD"); exit (EXIT_FAILURE); }
1.8. User Controls
Devices typically have a number of user-settable controlssuch as brightness, saturation and so on, which would be presented tothe user on a graphical user interface. But, different deviceswill have different controls available, and furthermore, the range ofpossible values, and the default value will vary from device todevice. The control ioctls provide the information and a mechanism tocreate a nice user interface for these controls that will workcorrectly with any device.
All controls are accessed using an ID value. V4L2 definesseveral IDs for specific purposes. Drivers can also implement theirown custom controls usingV4L2_CID_PRIVATE_BASE
and higher values. The pre-defined control IDs have the prefixV4L2_CID_
, and are listed inTable 1-1. The ID is used when querying the attributes ofa control, and when getting or setting the current value.
Generally applications should present controls to the userwithout assumptions about their purpose. Each control comes with aname string the user is supposed to understand. When the purpose isnon-intuitive the driver writer should provide a user manual, a userinterface plug-in or a driver specific panel application. PredefinedIDs were introduced to change a few controls programmatically, forexample to mute a device during a channel switch.
Drivers may enumerate different controls after switchingthe current video input or output, tuner or modulator, or audio inputor output. Different in the sense of other bounds, another default andcurrent value, step size or other menu items. A control with a certaincustom ID can also change name andtype.[9] Control values are stored globally, they do notchange when switching except to stay within the reported bounds. Theyalso do not change e. g. when the device is opened or closed, when thetuner radio frequency is changed or generally never withoutapplication request. Since V4L2 specifies no event mechanism, panelapplications intended to cooperate with other panel applications (bethey built into a larger application, as a TV viewer) may need toregularly poll control values to update their userinterface.[10]
Table 1-1. Control IDs
ID | Type | Description |
---|---|---|
V4L2_CID_BASE |
First predefined ID, equal toV4L2_CID_BRIGHTNESS . |
|
V4L2_CID_USER_BASE |
Synonym of V4L2_CID_BASE . |
|
V4L2_CID_BRIGHTNESS |
integer | Picture brightness, or more precisely, the blacklevel. |
V4L2_CID_CONTRAST |
integer | Picture contrast or luma gain. |
V4L2_CID_SATURATION |
integer | Picture color saturation or chroma gain. |
V4L2_CID_HUE |
integer | Hue or color balance. |
V4L2_CID_AUDIO_VOLUME |
integer | Overall audio volume. Note some drivers alsoprovide an OSS or ALSA mixer interface. |
V4L2_CID_AUDIO_BALANCE |
integer | Audio stereo balance. Minimum corresponds to allthe way left, maximum to right. |
V4L2_CID_AUDIO_BASS |
integer | Audio bass adjustment. |
V4L2_CID_AUDIO_TREBLE |
integer | Audio treble adjustment. |
V4L2_CID_AUDIO_MUTE |
boolean | Mute audio, i. e. set the volume to zero, howeverwithout affecting V4L2_CID_AUDIO_VOLUME . LikeALSA drivers, V4L2 drivers must mute at load time to avoid excessivenoise. Actually the entire device should be reset to a low powerconsumption state. |
V4L2_CID_AUDIO_LOUDNESS |
boolean | Loudness mode (bass boost). |
V4L2_CID_BLACK_LEVEL |
integer | Another name for brightness (not a synonym ofV4L2_CID_BRIGHTNESS ). This control is deprecatedand should not be used in new drivers and applications. |
V4L2_CID_AUTO_WHITE_BALANCE |
boolean | Automatic white balance (cameras). |
V4L2_CID_DO_WHITE_BALANCE |
button | This is an action control. When set (the value isignored), the device will do a white balance and then hold the currentsetting. Contrast this with the booleanV4L2_CID_AUTO_WHITE_BALANCE , which, whenactivated, keeps adjusting the white balance. |
V4L2_CID_RED_BALANCE |
integer | Red chroma balance. |
V4L2_CID_BLUE_BALANCE |
integer | Blue chroma balance. |
V4L2_CID_GAMMA |
integer | Gamma adjust. |
V4L2_CID_WHITENESS |
integer | Whiteness for grey-scale devices. This is a synonymfor V4L2_CID_GAMMA . This control is deprecatedand should not be used in new drivers and applications. |
V4L2_CID_EXPOSURE |
integer | Exposure (cameras). [Unit?] |
V4L2_CID_AUTOGAIN |
boolean | Automatic gain/exposure control. |
V4L2_CID_GAIN |
integer | Gain control. |
V4L2_CID_HFLIP |
boolean | Mirror the picture horizontally. |
V4L2_CID_VFLIP |
boolean | Mirror the picture vertically. |
V4L2_CID_HCENTER_DEPRECATED (formerly V4L2_CID_HCENTER ) |
integer | Horizontal image centering. This control isdeprecated. New drivers and applications should use theCamera class controlsV4L2_CID_PAN_ABSOLUTE ,V4L2_CID_PAN_RELATIVE andV4L2_CID_PAN_RESET instead. |
V4L2_CID_VCENTER_DEPRECATED (formerly V4L2_CID_VCENTER ) |
integer | Vertical image centering. Centering is intended tophysically adjust cameras. For image cropping seeSection 1.11, for clippingSection 4.2. Thiscontrol is deprecated. New drivers and applications should use theCamera class controlsV4L2_CID_TILT_ABSOLUTE ,V4L2_CID_TILT_RELATIVE andV4L2_CID_TILT_RESET instead. |
V4L2_CID_POWER_LINE_FREQUENCY |
integer | Enables a power line frequency filter to avoidflicker. Possible values are:V4L2_CID_POWER_LINE_FREQUENCY_DISABLED (0),V4L2_CID_POWER_LINE_FREQUENCY_50HZ (1) andV4L2_CID_POWER_LINE_FREQUENCY_60HZ (2). |
V4L2_CID_HUE_AUTO |
boolean | Enables automatic hue control by the device. Theeffect of setting V4L2_CID_HUE while automatichue control is enabled is undefined, drivers should ignore suchrequest. |
V4L2_CID_WHITE_BALANCE_TEMPERATURE |
integer | This control specifies the white balance settingsas a color temperature in Kelvin. A driver should have a minimum of2800 (incandescent) to 6500 (daylight). For more information aboutcolor temperature seeWikipedia. |
V4L2_CID_SHARPNESS |
integer | Adjusts the sharpness filters in a camera. Theminimum value disables the filters, higher values give a sharperpicture. |
V4L2_CID_BACKLIGHT_COMPENSATION |
integer | Adjusts the backlight compensation in a camera. Theminimum value disables backlight compensation. |
V4L2_CID_LASTP1 |
End of the predefined control IDs (currentlyV4L2_CID_BACKLIGHT_COMPENSATION + 1). |
|
V4L2_CID_PRIVATE_BASE |
ID of the first custom (driver specific) control.Applications depending on particular custom controls should check thedriver name and version, seeSection 1.2. |
Applications can enumerate the available controls with theVIDIOC_QUERYCTRL
andVIDIOC_QUERYMENU
ioctls, get and set acontrol value with theVIDIOC_G_CTRL
andVIDIOC_S_CTRL
ioctls.Drivers must implementVIDIOC_QUERYCTRL
,VIDIOC_G_CTRL
andVIDIOC_S_CTRL
when the device has one or morecontrols,VIDIOC_QUERYMENU
when it has one ormore menu type controls.
Example 1-8. Enumerating all controls
struct v4l2_queryctrl queryctrl; struct v4l2_querymenu querymenu; static void enumerate_menu (void) { printf (" Menu items:\n"); memset (&querymenu, 0, sizeof (querymenu)); querymenu.id = queryctrl.id; for (querymenu.index = queryctrl.minimum; querymenu.index <= queryctrl.maximum; querymenu.index++) { if (0 == ioctl (fd,VIDIOC_QUERYMENU
, &querymenu)) { printf (" %s\n", querymenu.name); } else { perror ("VIDIOC_QUERYMENU"); exit (EXIT_FAILURE); } } } memset (&queryctrl, 0, sizeof (queryctrl)); for (queryctrl.id = V4L2_CID_BASE; queryctrl.id < V4L2_CID_LASTP1; queryctrl.id++) { if (0 == ioctl (fd,VIDIOC_QUERYCTRL
, &queryctrl)) { if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) continue; printf ("Control %s\n", queryctrl.name); if (queryctrl.type == V4L2_CTRL_TYPE_MENU) enumerate_menu (); } else { if (errno == EINVAL) continue; perror ("VIDIOC_QUERYCTRL"); exit (EXIT_FAILURE); } } for (queryctrl.id = V4L2_CID_PRIVATE_BASE;; queryctrl.id++) { if (0 == ioctl (fd,VIDIOC_QUERYCTRL
, &queryctrl)) { if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) continue; printf ("Control %s\n", queryctrl.name); if (queryctrl.type == V4L2_CTRL_TYPE_MENU) enumerate_menu (); } else { if (errno == EINVAL) break; perror ("VIDIOC_QUERYCTRL"); exit (EXIT_FAILURE); } }
Example 1-9. Changing controls
struct v4l2_queryctrl queryctrl; struct v4l2_control control; memset (&queryctrl, 0, sizeof (queryctrl)); queryctrl.id = V4L2_CID_BRIGHTNESS; if (-1 == ioctl (fd,VIDIOC_QUERYCTRL
, &queryctrl)) { if (errno != EINVAL) { perror ("VIDIOC_QUERYCTRL"); exit (EXIT_FAILURE); } else { printf ("V4L2_CID_BRIGHTNESS is not supported\n"); } } else if (queryctrl.flags & V4L2_CTRL_FLAG_DISABLED) { printf ("V4L2_CID_BRIGHTNESS is not supported\n"); } else { memset (&control, 0, sizeof (control)); control.id = V4L2_CID_BRIGHTNESS; control.value = queryctrl.default_value; if (-1 == ioctl (fd,VIDIOC_S_CTRL
, &control)) { perror ("VIDIOC_S_CTRL"); exit (EXIT_FAILURE); } } memset (&control, 0, sizeof (control)); control.id = V4L2_CID_CONTRAST; if (0 == ioctl (fd,VIDIOC_G_CTRL
, &control)) { control.value += 1; /* The driver may clamp the value or return ERANGE, ignored here */ if (-1 == ioctl (fd,VIDIOC_S_CTRL
, &control) && errno != ERANGE) { perror ("VIDIOC_S_CTRL"); exit (EXIT_FAILURE); } /* Ignore if V4L2_CID_CONTRAST is unsupported */ } else if (errno != EINVAL) { perror ("VIDIOC_G_CTRL"); exit (EXIT_FAILURE); } control.id = V4L2_CID_AUDIO_MUTE; control.value = TRUE; /* silence */ /* Errors ignored */ ioctl (fd, VIDIOC_S_CTRL, &control);
1.9. Extended Controls
1.9.1. Introduction
The control mechanism as originally designed was meantto be used for user settings (brightness, saturation, etc). However,it turned out to be a very useful model for implementing morecomplicated driver APIs where each driver implements only a subset ofa larger API.
The MPEG encoding API was the driving force behinddesigning and implementing this extended control mechanism: the MPEGstandard is quite large and the currently supported hardware MPEGencoders each only implement a subset of this standard. Further more,many parameters relating to how the video is encoded into an MPEGstream are specific to the MPEG encoding chip since the MPEG standardonly defines the format of the resulting MPEG stream, not how thevideo is actually encoded into that format.
Unfortunately, the original control API lacked somefeatures needed for these new uses and so it was extended into the(not terribly originally named) extended control API.
1.9.2. The Extended Control API
Three new ioctls are available: VIDIOC_G_EXT_CTRLS
,VIDIOC_S_EXT_CTRLS
andVIDIOC_TRY_EXT_CTRLS
. These ioctls act onarrays of controls (as opposed to theVIDIOC_G_CTRL
andVIDIOC_S_CTRL
ioctls that act on a single control). This is neededsince it is often required to atomically change several controls atonce.
Each of the new ioctls expects a pointer to astruct v4l2_ext_controls. This structure contains a pointer to the controlarray, a count of the number of controls in that array and a controlclass. Control classes are used to group similar controls into asingle class. For example, control classV4L2_CTRL_CLASS_USER
contains all user controls(i. e. all controls that can also be set using the oldVIDIOC_S_CTRL
ioctl). Control classV4L2_CTRL_CLASS_MPEG
contains all controlsrelating to MPEG encoding, etc.
All controls in the control array must belong to thespecified control class. An error is returned if this is not thecase.
It is also possible to use an empty control array (count== 0) to check whether the specified control class issupported.
The control array is a struct v4l2_ext_control array. Thev4l2_ext_control
structure is very similar tostruct v4l2_control, except for the fact that it also allows for 64-bitvalues and pointers to be passed (although the latter is not yet usedanywhere).
It is important to realize that due to the flexibility ofcontrols it is necessary to check whether the control you want to setactually is supported in the driver and what the valid range of valuesis. So use theVIDIOC_QUERYCTRL
andVIDIOC_QUERYMENU
ioctls tocheck this. Also note that it is possible that some of the menuindices in a control of typeV4L2_CTRL_TYPE_MENU
may not be supported (VIDIOC_QUERYMENU
willreturn an error). A good example is the list of supported MPEG audiobitrates. Some drivers only support one or two bitrates, otherssupport a wider range.
1.9.3. Enumerating Extended Controls
The recommended way to enumerate over the extendedcontrols is by using VIDIOC_QUERYCTRL
in combination with theV4L2_CTRL_FLAG_NEXT_CTRL
flag:
struct v4l2_queryctrl qctrl;
qctrl.id = V4L2_CTRL_FLAG_NEXT_CTRL;
while (0 == ioctl (fd, VIDIOC_QUERYCTRL
, &qctrl)) {
/* ... */
qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL;
}
The initial control ID is set to 0 ORed with theV4L2_CTRL_FLAG_NEXT_CTRL
flag. TheVIDIOC_QUERYCTRL
ioctl will return the firstcontrol with a higher ID than the specified one. When no such controlsare found an error is returned.
If you want to get all controls within a specific controlclass, then you can set the initialqctrl.id
value to the control class and addan extra check to break out of the loop when a control of anothercontrol class is found:
qctrl.id = V4L2_CTRL_CLASS_MPEG | V4L2_CTRL_FLAG_NEXT_CTRL;
while (0 == ioctl (fd, VIDIOC_QUERYCTRL
, &qctrl)) {
if (V4L2_CTRL_ID2CLASS (qctrl.id) != V4L2_CTRL_CLASS_MPEG)
break;
/* ... */
qctrl.id |= V4L2_CTRL_FLAG_NEXT_CTRL;
}
The 32-bit qctrl.id
value issubdivided into three bit ranges: the top 4 bits are reserved forflags (e. g.V4L2_CTRL_FLAG_NEXT_CTRL
) and are notactually part of the ID. The remaining 28 bits form the control ID, ofwhich the most significant 12 bits define the control class and theleast significant 16 bits identify the control within the controlclass. It is guaranteed that these last 16 bits are always non-zerofor controls. The range of 0x1000 and up are reserved fordriver-specific controls. The macroV4L2_CTRL_ID2CLASS(id)
returns the control classID based on a control ID.
If the driver does not support extended controls, thenVIDIOC_QUERYCTRL
will fail when used incombination withV4L2_CTRL_FLAG_NEXT_CTRL
. Inthat case the old method of enumerating control should be used (see1.8). But if it is supported, then it is guaranteed to enumerate overall controls, including driver-private controls.
1.9.4. Creating Control Panels
It is possible to create control panels for a graphicaluser interface where the user can select the various controls.Basically you will have to iterate over all controls using the methoddescribed above. Each control class starts with a control of typeV4L2_CTRL_TYPE_CTRL_CLASS
.VIDIOC_QUERYCTRL
will return the name of thiscontrol class which can be used as the title of a tab page within acontrol panel.
The flags field of struct v4l2_queryctrl also contains hints onthe behavior of the control. See theVIDIOC_QUERYCTRL
documentationfor more details.
1.9.5. MPEG Control Reference
Below all controls within the MPEG control class aredescribed. First the generic controls, then controls specific forcertain hardware.
1.9.5.1. Generic MPEG Controls
Table 1-2. MPEG Control IDs
ID | Type | ||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Description | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_CLASS |
class | ||||||||||||||||||||||||||||||
The MPEG classdescriptor. Calling VIDIOC_QUERYCTRL for this control will return adescription of this control class. This description can be used as thecaption of a Tab page in a GUI, for example. |
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_STREAM_TYPE |
enum | ||||||||||||||||||||||||||||||
The MPEG-1, -2 or -4output stream type. One cannot assume anything here. Each hardwareMPEG encoder tends to support different subsets of the available MPEGstream types. The currently defined stream types are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_STREAM_PID_PMT |
integer | ||||||||||||||||||||||||||||||
Program Map TablePacket ID for the MPEG transport stream (default 16) | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_STREAM_PID_AUDIO |
integer | ||||||||||||||||||||||||||||||
Audio Packet ID forthe MPEG transport stream (default 256) | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_STREAM_PID_VIDEO |
integer | ||||||||||||||||||||||||||||||
Video Packet ID forthe MPEG transport stream (default 260) | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_STREAM_PID_PCR |
integer | ||||||||||||||||||||||||||||||
Packet ID for theMPEG transport stream carrying PCR fields (default 259) | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_STREAM_PES_ID_AUDIO |
integer | ||||||||||||||||||||||||||||||
Audio ID for MPEGPES | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_STREAM_PES_ID_VIDEO |
integer | ||||||||||||||||||||||||||||||
Video ID for MPEGPES | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_STREAM_VBI_FMT |
enum | ||||||||||||||||||||||||||||||
Some cards can embedVBI data (e. g. Closed Caption, Teletext) into the MPEG stream. Thiscontrol selects whether VBI data should be embedded, and if so, whatembedding method should be used. The list of possible VBI formatsdepends on the driver. The currently defined VBI format typesare: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ |
enum | ||||||||||||||||||||||||||||||
MPEG Audio samplingfrequency. Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_ENCODING |
enum | ||||||||||||||||||||||||||||||
MPEG Audio encoding.Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_L1_BITRATE |
enum | ||||||||||||||||||||||||||||||
Layer I bitrate.Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_L2_BITRATE |
enum | ||||||||||||||||||||||||||||||
Layer II bitrate.Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_L3_BITRATE |
enum | ||||||||||||||||||||||||||||||
Layer III bitrate.Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_MODE |
enum | ||||||||||||||||||||||||||||||
MPEG Audio mode.Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_MODE_EXTENSION |
enum | ||||||||||||||||||||||||||||||
Joint Stereoaudio mode extension. In Layer I and II they indicate which subbandsare in intensity stereo. All other subbands are coded in stereo. LayerIII is not (yet) supported. Possible valuesare: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_EMPHASIS |
enum | ||||||||||||||||||||||||||||||
Audio Emphasis.Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_CRC |
enum | ||||||||||||||||||||||||||||||
CRC method. Possiblevalues are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_AUDIO_MUTE |
bool | ||||||||||||||||||||||||||||||
Mutes the audio whencapturing. This is not done by muting audio hardware, which can stillproduce a slight hiss, but in the encoder itself, guaranteeing a fixedand reproducable audio bitstream. 0 = unmuted, 1 = muted. | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_ENCODING |
enum | ||||||||||||||||||||||||||||||
MPEG Video encodingmethod. Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_ASPECT |
enum | ||||||||||||||||||||||||||||||
Video aspect.Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_B_FRAMES |
integer | ||||||||||||||||||||||||||||||
Number of B-Frames(default 2) | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_GOP_SIZE |
integer | ||||||||||||||||||||||||||||||
GOP size (default12) | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_GOP_CLOSURE |
bool | ||||||||||||||||||||||||||||||
GOP closure (default1) | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_PULLDOWN |
bool | ||||||||||||||||||||||||||||||
Enable 3:2 pulldown(default 0) | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_BITRATE_MODE |
enum | ||||||||||||||||||||||||||||||
Video bitrate mode.Possible values are: | |||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_BITRATE |
integer | ||||||||||||||||||||||||||||||
Video bitrate in bitsper second. | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_BITRATE_PEAK |
integer | ||||||||||||||||||||||||||||||
Peak video bitrate inbits per second. Must be larger or equal to the average video bitrate.It is ignored if the video bitrate mode is set to constantbitrate. | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION |
integer | ||||||||||||||||||||||||||||||
For every capturedframe, skip this many subsequent frames (default 0). | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_MUTE |
bool | ||||||||||||||||||||||||||||||
"Mutes" the video to afixed color when capturing. This is useful for testing, to produce afixed video bitstream. 0 = unmuted, 1 = muted. | |||||||||||||||||||||||||||||||
V4L2_CID_MPEG_VIDEO_MUTE_YUV |
integer | ||||||||||||||||||||||||||||||
Sets the "mute" colorof the video. The supplied 32-bit integer is interpreted as follows (bit0 = least significant bit): | |||||||||||||||||||||||||||||||
|
1.9.5.2. CX2341x MPEG Controls
The following MPEG class controls deal with MPEGencoding settings that are specific to the Conexant CX23415 andCX23416 MPEG encoding chips.
Table 1-3. CX2341x Control IDs
ID | Type | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Description | |||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE |
enum | ||||||||||||
Sets the SpatialFilter mode (default MANUAL ). Possible valuesare: |
|||||||||||||
|
|||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER |
integer (0-15) | ||||||||||||
The setting for theSpatial Filter. 0 = off, 15 = maximum. (Default is 0.) | |||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE |
enum | ||||||||||||
Select the algorithmto use for the Luma Spatial Filter (default1D_HOR ). Possible values: |
|||||||||||||
|
|||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE |
enum | ||||||||||||
Select the algorithmfor the Chroma Spatial Filter (default 1D_HOR ).Possible values are: |
|||||||||||||
|
|||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE |
enum | ||||||||||||
Sets the TemporalFilter mode (default MANUAL ). Possible valuesare: |
|||||||||||||
|
|||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER |
integer (0-31) | ||||||||||||
The setting for theTemporal Filter. 0 = off, 31 = maximum. (Default is 8 for full-scalecapturing and 0 for scaled capturing.) | |||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE |
enum | ||||||||||||
Median Filter Type(default OFF ). Possible values are: |
|||||||||||||
|
|||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_BOTTOM |
integer (0-255) | ||||||||||||
Threshold above whichthe luminance median filter is enabled (default 0) | |||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_TOP |
integer (0-255) | ||||||||||||
Threshold below whichthe luminance median filter is enabled (default 255) | |||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_BOTTOM |
integer (0-255) | ||||||||||||
Threshold above whichthe chroma median filter is enabled (default 0) | |||||||||||||
V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_TOP |
integer (0-255) | ||||||||||||
Threshold below whichthe chroma median filter is enabled (default 255) | |||||||||||||
V4L2_CID_MPEG_CX2341X_STREAM_INSERT_NAV_PACKETS |
bool | ||||||||||||
The CX2341X MPEG encodercan insert one empty MPEG-2 PES packet into the stream between everyfour video frames. The packet size is 2048 bytes, including thepacket_start_code_prefix and stream_id fields. The stream_id is 0xBF(private stream 2). The payload consists of 0x00 bytes, to be filledin by the application. 0 = do not insert, 1 = insert packets. |
1.9.6. Camera Control Reference
The Camera class includes controls for mechanical (orequivalent digital) features of a device such as controllable lensesor sensors.
Table 1-4. Camera Control IDs
ID | Type | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Description | |||||||||||
V4L2_CID_CAMERA_CLASS |
class | ||||||||||
The Camera classdescriptor. Calling VIDIOC_QUERYCTRL for this control will return adescription of this control class. |
|||||||||||
V4L2_CID_EXPOSURE_AUTO |
integer | ||||||||||
Enables automaticadjustments of the exposure time and/or iris aperture. The effect ofmanual changes of the exposure time or iris aperture while thesefeatures are enabled is undefined, drivers should ignore suchrequests. Possible values are: | |||||||||||
|
|||||||||||
V4L2_CID_EXPOSURE_ABSOLUTE |
integer | ||||||||||
Determines the exposuretime of the camera sensor. The exposure time is limited by the frameinterval. Drivers should interpret the values as 100 µs units,where the value 1 stands for 1/10000th of a second, 10000 for 1 secondand 100000 for 10 seconds. | |||||||||||
V4L2_CID_EXPOSURE_AUTO_PRIORITY |
boolean | ||||||||||
WhenV4L2_CID_EXPOSURE_AUTO is set toAUTO orSHUTTER_PRIORITY ,this control determines if the device may dynamically vary the framerate. By default this feature is disabled (0) and the frame rate mustremain constant. |
|||||||||||
V4L2_CID_PAN_RELATIVE |
integer | ||||||||||
This control turns thecamera horizontally by the specified amount. The unit is undefined. Apositive value moves the camera to the right (clockwise when viewedfrom above), a negative value to the left. A value of zero does notcause motion. | |||||||||||
V4L2_CID_TILT_RELATIVE |
integer | ||||||||||
This control turns thecamera vertically by the specified amount. The unit is undefined. Apositive value moves the camera up, a negative value down. A value ofzero does not cause motion. | |||||||||||
V4L2_CID_PAN_RESET |
boolean | ||||||||||
When this control is setto TRUE (1), the camera moves horizontally to thedefault position. |
|||||||||||
V4L2_CID_TILT_RESET |
boolean | ||||||||||
When this control is setto TRUE (1), the camera moves vertically to thedefault position. |
|||||||||||
V4L2_CID_PAN_ABSOLUTE |
integer | ||||||||||
This controlturns the camera horizontally to the specified position. Positivevalues move the camera to the right (clockwise when viewed from above),negative values to the left. Drivers should interpret the values as arcseconds, with valid values between -180 * 3600 and +180 * 3600inclusive. | |||||||||||
V4L2_CID_TILT_ABSOLUTE |
integer | ||||||||||
This controlturns the camera vertically to the specified position. Positive valuesmove the camera up, negative values down. Drivers should interpret thevalues as arc seconds, with valid values between -180 * 3600 and +180* 3600 inclusive. | |||||||||||
V4L2_CID_FOCUS_ABSOLUTE |
integer | ||||||||||
This control sets thefocal point of the camera to the specified position. The unit isundefined. Positive values set the focus closer to the camera,negative values towards infinity. | |||||||||||
V4L2_CID_FOCUS_RELATIVE |
integer | ||||||||||
This control moves thefocal point of the camera by the specified amount. The unit isundefined. Positive values move the focus closer to the camera,negative values towards infinity. | |||||||||||
V4L2_CID_FOCUS_AUTO |
boolean | ||||||||||
Enables automatic focusadjustments. The effect of manual focus adjustments while this featureis enabled is undefined, drivers should ignore such requests. | |||||||||||
1.10. Data Formats
1.10.1. Data Format Negotiation
Different devices exchange different kinds of data withapplications, for example video images, raw or sliced VBI data, RDSdatagrams. Even within one kind many different formats are possible,in particular an abundance of image formats. Although drivers mustprovide a default and the selection persists across closing andreopening a device, applications should always negotiate a data formatbefore engaging in data exchange. Negotiation means the applicationasks for a particular format and the driver selects and reports thebest the hardware can do to satisfy the request. Of courseapplications can also just query the current selection.
A single mechanism exists to negotiate all data formatsusing the aggregate struct v4l2_format and theVIDIOC_G_FMT
andVIDIOC_S_FMT
ioctls. Additionally theVIDIOC_TRY_FMT
ioctl can beused to examine what the hardwarecould do,without actually selecting a new data format. The data formatssupported by the V4L2 API are covered in the respective device sectioninChapter 4. For a closer look at image formats seeChapter 2.
The VIDIOC_S_FMT
ioctl is a majorturning-point in the initialization sequence. Prior to this pointmultiple panel applications can access the same device concurrently toselect the current input, change controls or modify other properties.The first VIDIOC_S_FMT
assigns a logical stream(video data, VBI data etc.) exclusively to one file descriptor.
Exclusive means no other application, more precisely noother file descriptor, can grab this stream or change deviceproperties inconsistent with the negotiated parameters. A videostandard change for example, when the new standard uses a differentnumber of scan lines, can invalidate the selected image format.Therefore only the file descriptor owning the stream can makeinvalidating changes. Accordingly multiple file descriptors whichgrabbed different logical streams prevent each other from interferingwith their settings. When for example video overlay is about to startor already in progress, simultaneous video capturing may be restrictedto the same cropping and image size.
When applications omit theVIDIOC_S_FMT
ioctl its locking side effects areimplied by the next step, the selection of an I/O method with theVIDIOC_REQBUFS
ioctl or implicit with the first read()
orwrite()
call.
Generally only one logical stream can be assigned to afile descriptor, the exception being drivers permitting simultaneousvideo capturing and overlay using the same file descriptor forcompatibility with V4L and earlier versions of V4L2. Switching thelogical stream or returning into "panel mode" is possible by closingand reopening the device. Driversmay support aswitch usingVIDIOC_S_FMT
.
All drivers exchanging data withapplications must support the VIDIOC_G_FMT
andVIDIOC_S_FMT
ioctl. Implementation of theVIDIOC_TRY_FMT
is highly recommended butoptional.
1.10.2. Image Format Enumeration
Apart of the generic format negotiation functionsa special ioctl to enumerate all image formats supported by videocapture, overlay or output devices is available.[11]
The VIDIOC_ENUM_FMT
ioctl must be supportedby all drivers exchanging image data with applications.
Important: Drivers are not supposed to convert image formats inkernel space. They must enumerate only formats directly supported bythe hardware. If necessary driver writers should publish an exampleconversion routine or library for integration into applications.
1.11. Image Cropping, Insertion and Scaling
Some video capture devices can sample a subsection of thepicture and shrink or enlarge it to an image of arbitrary size. Wecall these abilities cropping and scaling. Some video output devicescan scale an image up or down and insert it at an arbitrary scan lineand horizontal offset into a video signal.
Applications can use the following API to select an area inthe video signal, query the default area and the hardware limits.Despite their name, theVIDIOC_CROPCAP
,VIDIOC_G_CROP
andVIDIOC_S_CROP
ioctls apply to input as well as outputdevices.
Scaling requires a source and a target. On a video captureor overlay device the source is the video signal, and the croppingioctls determine the area actually sampled. The target are imagesread by the application or overlaid onto the graphics screen. Theirsize (and position for an overlay) is negotiated with theVIDIOC_G_FMT
andVIDIOC_S_FMT
ioctls.
On a video output device the source are the images passed inby the application, and their size is again negotiated with theVIDIOC_G/S_FMT
ioctls, or may be encoded in acompressed video stream. The target is the video signal, and thecropping ioctls determine the area where the images areinserted.
Source and target rectangles are defined even if the devicedoes not support scaling or theVIDIOC_G/S_CROP
ioctls. Their size (and position where applicable) will be fixed inthis case.All capture and output device must support theVIDIOC_CROPCAP
ioctl such that applications candetermine if scaling takes place.
1.11.1. Cropping Structures
For capture devices the coordinates of the top leftcorner, width and height of the area which can be sampled is given bythebounds
substructure of thestruct v4l2_cropcap returned by theVIDIOC_CROPCAP
ioctl. To support a wide range of hardware this specification does notdefine an origin or units. However by convention drivers shouldhorizontally count unscaled samples relative to 0H (the leading edgeof the horizontal sync pulse, see Figure 4-1).Vertically ITU-R linenumbers of the first field (Figure 4-2,Figure 4-3), multiplied by two if the driver can capture bothfields.
The top left corner, width and height of the sourcerectangle, that is the area actually sampled, is given by struct v4l2_cropusing the same coordinate system as struct v4l2_cropcap. Applications canuse the VIDIOC_G_CROP
andVIDIOC_S_CROP
ioctls to get and set thisrectangle. It must lie completely within the capture boundaries andthe driver may further adjust the requested size and/or positionaccording to hardware limitations.
Each capture device has a default source rectangle, givenby the defrect
substructure ofstruct v4l2_cropcap. The center of this rectangle shall align with thecenter of the active picture area of the video signal, and cover whatthe driver writer considers the complete picture. Drivers shall resetthe source rectangle to the default when the driver is first loaded,but not later.
For output devices these structures and ioctls are usedaccordingly, defining thetarget rectangle wherethe images will be inserted into the video signal.
1.11.2. Scaling Adjustments
Video hardware can have various cropping, insertion andscaling limitations. It may only scale up or down, support onlydiscrete scaling factors, or have different scaling abilities inhorizontal and vertical direction. Also it may not support scaling atall. At the same time the struct v4l2_crop rectangle may have to bealigned, and both the source and target rectangles may have arbitraryupper and lower size limits. In particular the maximumwidth
and height
in struct v4l2_crop may be smaller than thestruct v4l2_cropcap.bounds
area. Therefore, asusual, drivers are expected to adjust the requested parameters andreturn the actual values selected.
Applications can change the source or the target rectanglefirst, as they may prefer a particular image size or a certain area inthe video signal. If the driver has to adjust both to satisfy hardwarelimitations, the last requested rectangle shall take priority, and thedriver should preferably adjust the opposite one. The VIDIOC_TRY_FMT
ioctl however shall not change the driver state and therefore onlyadjust the requested rectangle.
Suppose scaling on a video capture device is restricted toa factor 1:1 or 2:1 in either direction and the target image size mustbe a multiple of 16 × 16 pixels. The source croppingrectangle is set to defaults, which are also the upper limit in thisexample, of 640 × 400 pixels at offset 0, 0. Anapplication requests an image size of 300 × 225pixels, assuming video will be scaled down from the "full picture"accordingly. The driver sets the image size to the closest possiblevalues 304 × 224, then chooses the cropping rectangleclosest to the requested size, that is 608 × 224(224 × 2:1 would exceed the limit 400). The offset0, 0 is still valid, thus unmodified. Given the default croppingrectangle reported byVIDIOC_CROPCAP
theapplication can easily propose another offset to center the croppingrectangle.
Now the application may insist on covering an area using apicture aspect ratio closer to the original request, so it asks for acropping rectangle of 608 × 456 pixels. The presentscaling factors limit cropping to 640 × 384, so thedriver returns the cropping size 608 × 384 and adjuststhe image size to closest possible 304 × 192.
1.11.3. Examples
Source and target rectangles shall remain unchanged acrossclosing and reopening a device, such that piping data into or out of adevice will work without special preparations. More advancedapplications should ensure the parameters are suitable before startingI/O.
Example 1-10. Resetting the cropping parameters
(A video capture device is assumed; changeV4L2_BUF_TYPE_VIDEO_CAPTURE
for otherdevices.)
struct v4l2_cropcap cropcap; struct v4l2_crop crop; memset (&cropcap, 0, sizeof (cropcap)); cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == ioctl (fd,VIDIOC_CROPCAP
, &cropcap)) { perror ("VIDIOC_CROPCAP"); exit (EXIT_FAILURE); } memset (&crop, 0, sizeof (crop)); crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; crop.c = cropcap.defrect; /* Ignore if cropping is not supported (EINVAL). */ if (-1 == ioctl (fd,VIDIOC_S_CROP
, &crop) && errno != EINVAL) { perror ("VIDIOC_S_CROP"); exit (EXIT_FAILURE); }
Example 1-11. Simple downscaling
(A video capture device is assumed.)
struct v4l2_cropcap cropcap;
struct v4l2_format format;
reset_cropping_parameters ();
/* Scale down to 1/4 size of full picture. */
memset (&format, 0, sizeof (format)); /* defaults */
format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
format.fmt.pix.width = cropcap.defrect.width >> 1;
format.fmt.pix.height = cropcap.defrect.height >> 1;
format.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
if (-1 == ioctl (fd, VIDIOC_S_FMT
, &format)) {
perror ("VIDIOC_S_FORMAT");
exit (EXIT_FAILURE);
}
/* We could check the actual image size now, the actual scaling factor
or if the driver can scale at all. */
Example 1-12. Selecting an output area
struct v4l2_cropcap cropcap; struct v4l2_crop crop; memset (&cropcap, 0, sizeof (cropcap)); cropcap.type = V4L2_BUF_TYPE_VIDEO_OUTPUT; if (-1 == ioctl (fd, VIDIOC_CROPCAP, &cropcap)) { perror ("VIDIOC_CROPCAP"); exit (EXIT_FAILURE); } memset (&crop, 0, sizeof (crop)); crop.type = V4L2_BUF_TYPE_VIDEO_OUTPUT; crop.c = cropcap.defrect; /* Scale the width and height to 50 % of their original size and center the output. */ crop.c.width /= 2; crop.c.height /= 2; crop.c.left += crop.c.width / 2; crop.c.top += crop.c.height / 2; /* Ignore if cropping is not supported (EINVAL). */ if (-1 == ioctl (fd, VIDIOC_S_CROP, &crop) && errno != EINVAL) { perror ("VIDIOC_S_CROP"); exit (EXIT_FAILURE); }
Example 1-13. Current scaling factor and pixel aspect
(A video capture device is assumed.)
struct v4l2_cropcap cropcap; struct v4l2_crop crop; struct v4l2_format format; double hscale, vscale; double aspect; int dwidth, dheight; memset (&cropcap, 0, sizeof (cropcap)); cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == ioctl (fd,VIDIOC_CROPCAP
, &cropcap)) { perror ("VIDIOC_CROPCAP"); exit (EXIT_FAILURE); } memset (&crop, 0, sizeof (crop)); crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == ioctl (fd,VIDIOC_G_CROP
, &crop)) { if (errno != EINVAL) { perror ("VIDIOC_G_CROP"); exit (EXIT_FAILURE); } /* Cropping not supported. */ crop.c = cropcap.defrect; } memset (&format, 0, sizeof (format)); format.fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; if (-1 == ioctl (fd,VIDIOC_G_FMT
, &format)) { perror ("VIDIOC_G_FMT"); exit (EXIT_FAILURE); } /* The scaling applied by the driver. */ hscale = format.fmt.pix.width / (double) crop.c.width; vscale = format.fmt.pix.height / (double) crop.c.height; aspect = cropcap.pixelaspect.numerator / (double) cropcap.pixelaspect.denominator; aspect = aspect * hscale / vscale; /* Devices following ITU-R BT.601 do not capture square pixels. For playback on a computer monitor we should scale the images to this size. */ dwidth = format.fmt.pix.width / aspect; dheight = format.fmt.pix.height;
1.12. Streaming Parameters
Streaming parameters are intended to optimize the videocapture process as well as I/O. Presently applications can request ahigh quality capture mode with theVIDIOC_S_PARM
ioctl.
The current video standard determines a nominal number offrames per second. If less than this number of frames is to becaptured or output, applications can request frame skipping orduplicating on the driver side. This is especially useful when usingtheread()
orwrite()
, which are not augmented by timestampsor sequence counters, and to avoid unneccessary data copying.
Finally these ioctls can be used to determine the number ofbuffers used internally by a driver in read/write mode. Forimplications see the section discussing theread()
function.
To get and set the streaming parameters applications callthe VIDIOC_G_PARM
and VIDIOC_S_PARM
ioctl, respectively. They takea pointer to a struct v4l2_streamparm, which contains a union holdingseparate parameters for input and output devices.
These ioctls are optional, drivers need not implementthem. If so, they return theEINVAL error code.
Chapter 2. Image Formats
The V4L2 API was primarily designed for devices exchangingimage data with applications. Thev4l2_pix_format
structure defines the formatand layout of an image in memory. Image formats are negotiated withtheVIDIOC_S_FMT
ioctl. (The explanations here focus on videocapturing and output, for overlay frame buffer formats see alsoVIDIOC_G_FBUF
.)
Table 2-1. struct v4l2_pix_format
__u32 | width |
Image width in pixels. |
__u32 | height |
Image height in pixels. |
Applications set these fields torequest an image size, drivers return the closest possible values. Incase of planar formats thewidth andheight applies to the largest plane. Toavoid ambiguities drivers must return values rounded up to a multipleof the scale factor of any smaller planes. For example when the imageformat is YUV 4:2:0,width andheight must be multiples of two. |
||
__u32 | pixelformat |
The pixel format or type of compression, set by theapplication. This is a little endianfour character code. V4L2 definesstandard RGB formats inTable 2-1, YUV formats inSection 2.5, and reserved codes inTable 2-8 |
enum v4l2_field | field |
Video images are typically interlaced. Applicationscan request to capture or output only the top or bottom field, or bothfields interlaced or sequentially stored in one buffer or alternatingin separate buffers. Drivers return the actual field order selected.For details see Section 3.6. |
__u32 | bytesperline |
Distance in bytes between the leftmost pixels in twoadjacent lines. |
Both applications and driverscan set this field to request padding bytes at the end of each line.Drivers however may ignore the value requested by the application,returning Video hardware may access padding bytes,therefore they must reside in accessible memory. Consider cases wherepadding bytes after the last line of an image cross a system pageboundary. Input devices may write padding bytes, the value isundefined. Output devices ignore the contents of paddingbytes. When the image format is planar the |
||
__u32 | sizeimage |
Size in bytes of the buffer to hold a complete image,set by the driver. Usually this isbytesperline timesheight . When the image consists of variablelength compressed data this is the maximum number of bytes required tohold an image. |
enum v4l2_colorspace | colorspace |
This information supplements thepixelformat and must be set by the driver,seeSection 2.2. |
__u32 | priv |
Reserved for custom (driver defined) additionalinformation about formats. When not used drivers and applications mustset this field to zero. |
2.1. Standard Image Formats
In order to exchange images between drivers andapplications, it is necessary to have standard image data formatswhich both sides will interpret the same way. V4L2 includes severalsuch formats, and this section is intended to be an unambiguousspecification of the standard image data formats in V4L2.
V4L2 drivers are not limited to these formats, however.Driver-specific formats are possible. In that case the application maydepend on a codec to convert images to one of the standard formatswhen needed. But the data can still be stored and retrieved in theproprietary format. For example, a device may support a proprietarycompressed format. Applications can still capture and save the data inthe compressed format, saving much disk space, and later use a codecto convert the images to the X Windows screen format when the video isto be displayed.
Even so, ultimately, some standard formats are needed, sothe V4L2 specification would not be complete without well-definedstandard formats.
The V4L2 standard formats are mainly uncompressed formats. Thepixels are always arranged in memory from left to right, and from topto bottom. The first byte of data in the image buffer is always forthe leftmost pixel of the topmost row. Following that is the pixelimmediately to its right, and so on until the end of the top row ofpixels. Following the rightmost pixel of the row there may be zero ormore bytes of padding to guarantee that each row of pixel data has acertain alignment. Following the pad bytes, if any, is data for theleftmost pixel of the second row from the top, and so on. The last rowhas just as many pad bytes after it as the other rows.
In V4L2 each format has an identifier which looks likePIX_FMT_XXX
, defined in thevideodev.h header file. These identifiersrepresentfour character codeswhich are also listed below, however they are not the same as thoseused in the Windows world.
2.2. Colorspaces
[intro]
- Gamma Correction
-
[to do]
E'R = f(R)
E'G = f(G)
E'B = f(B)
- Construction of luminance and color-differencesignals
-
[to do]
E'Y =CoeffR E'R+ CoeffG E'G+ CoeffB E'B
(E'R - E'Y) = E'R- CoeffR E'R- CoeffG E'G- CoeffB E'B
(E'B - E'Y) = E'B- CoeffR E'R- CoeffG E'G- CoeffB E'B
- Re-normalized color-difference signals
-
The color-difference signals are scaled back to unityrange [-0.5;+0.5]:
KB = 0.5 / (1 - CoeffB)
KR = 0.5 / (1 - CoeffR)
PB =KB (E'B - E'Y) = 0.5 (CoeffR / CoeffB) E'R+ 0.5 (CoeffG / CoeffB) E'G+ 0.5 E'B
PR =KR (E'R - E'Y) = 0.5 E'R+ 0.5 (CoeffG / CoeffR) E'G+ 0.5 (CoeffB / CoeffR) E'B
- Quantization
-
[to do]
Y' = (Lum. Levels - 1) · E'Y + Lum. Offset
CB = (Chrom. Levels - 1)· PB + Chrom. Offset
CR = (Chrom. Levels - 1)· PR + Chrom. Offset
Rounding to the nearest integer and clamping to the range[0;255] finally yields the digital color components Y'CbCrstored in YUV images.
Example 2-1. ITU-R Rec. BT.601 color conversion
Forward Transformation
int ER, EG, EB; /* gamma corrected RGB input [0;255] */ int Y1, Cb, Cr; /* output [0;255] */ double r, g, b; /* temporaries */ double y1, pb, pr; int clamp (double x) { int r = x; /* round to nearest */ if (r < 0) return 0; else if (r > 255) return 255; else return r; } r = ER / 255.0; g = EG / 255.0; b = EB / 255.0; y1 = 0.299 * r + 0.587 * g + 0.114 * b; pb = -0.169 * r - 0.331 * g + 0.5 * b; pr = 0.5 * r - 0.419 * g - 0.081 * b; Y1 = clamp (219 * y1 + 16); Cb = clamp (224 * pb + 128); Cr = clamp (224 * pr + 128); /* or shorter */ y1 = 0.299 * ER + 0.587 * EG + 0.114 * EB; Y1 = clamp ( (219 / 255.0) * y1 + 16); Cb = clamp (((224 / 255.0) / (2 - 2 * 0.114)) * (EB - y1) + 128); Cr = clamp (((224 / 255.0) / (2 - 2 * 0.299)) * (ER - y1) + 128);
Inverse Transformation
int Y1, Cb, Cr; /* gamma pre-corrected input [0;255] */ int ER, EG, EB; /* output [0;255] */ double r, g, b; /* temporaries */ double y1, pb, pr; int clamp (double x) { int r = x; /* round to nearest */ if (r < 0) return 0; else if (r > 255) return 255; else return r; } y1 = (255 / 219.0) * (Y1 - 16); pb = (255 / 224.0) * (Cb - 128); pr = (255 / 224.0) * (Cr - 128); r = 1.0 * y1 + 0 * pb + 1.402 * pr; g = 1.0 * y1 - 0.344 * pb - 0.714 * pr; b = 1.0 * y1 + 1.772 * pb + 0 * pr; ER = clamp (r * 255); /* [ok? one should prob. limit y1,pb,pr] */ EG = clamp (g * 255); EB = clamp (b * 255);
Table 2-2. enum v4l2_colorspace
Identifier | Value | Description | Chromaticities[a] | White Point | Gamma Correction | Luminance E'Y | Quantization | |||
---|---|---|---|---|---|---|---|---|---|---|
Red | Green | Blue | Y' | Cb, Cr | ||||||
V4L2_COLORSPACE_SMPTE170M |
1 | NTSC/PAL according to SMPTE 170M,ITU BT.601 | x = 0.630, y = 0.340 | x = 0.310, y = 0.595 | x = 0.155, y = 0.070 | x = 0.3127, y = 0.3290, Illuminant D65 | E' = 4.5 I for I ≤0.018,1.099 I0.45 - 0.099 for 0.018 < I | 0.299 E'R+ 0.587 E'G+ 0.114 E'B | 219 E'Y + 16 | 224 PB,R + 128 |
V4L2_COLORSPACE_SMPTE240M |
2 | 1125-Line (US) HDTV, see SMPTE 240M | x = 0.630, y = 0.340 | x = 0.310, y = 0.595 | x = 0.155, y = 0.070 | x = 0.3127, y = 0.3290, Illuminant D65 | E' = 4 I for I ≤0.0228,1.1115 I0.45 - 0.1115 for 0.0228 < I | 0.212 E'R+ 0.701 E'G+ 0.087 E'B | 219 E'Y + 16 | 224 PB,R + 128 |
V4L2_COLORSPACE_REC709 |
3 | HDTV and modern devices, see ITU BT.709 | x = 0.640, y = 0.330 | x = 0.300, y = 0.600 | x = 0.150, y = 0.060 | x = 0.3127, y = 0.3290, Illuminant D65 | E' = 4.5 I for I ≤0.018,1.099 I0.45 - 0.099 for 0.018 < I | 0.2125 E'R + 0.7154 E'G+ 0.0721 E'B | 219 E'Y + 16 | 224 PB,R + 128 |
V4L2_COLORSPACE_BT878 |
4 | Broken Bt878 extents[b],ITU BT.601 | ? | ? | ? | ? | ? | 0.299 E'R+ 0.587 E'G+ 0.114 E'B | 237 E'Y + 16 | 224 PB,R + 128 (probably) |
V4L2_COLORSPACE_470_SYSTEM_M |
5 | M/NTSC[c] according toITU BT.470,ITU BT.601 | x = 0.67, y = 0.33 | x = 0.21, y = 0.71 | x = 0.14, y = 0.08 | x = 0.310, y = 0.316, Illuminant C | ? | 0.299 E'R+ 0.587 E'G+ 0.114 E'B | 219 E'Y + 16 | 224 PB,R + 128 |
V4L2_COLORSPACE_470_SYSTEM_BG |
6 | 625-line PAL and SECAM systems according to ITU BT.470, ITU BT.601 | x = 0.64, y = 0.33 | x = 0.29, y = 0.60 | x = 0.15, y = 0.06 | x = 0.313, y = 0.329,Illuminant D65 | ? | 0.299 E'R+ 0.587 E'G+ 0.114 E'B | 219 E'Y + 16 | 224 PB,R + 128 |
V4L2_COLORSPACE_JPEG |
7 | JPEG Y'CbCr, see JFIF, ITU BT.601 | ? | ? | ? | ? | ? | 0.299 E'R+ 0.587 E'G+ 0.114 E'B | 256 E'Y + 16[d] | 256 PB,R + 128 |
V4L2_COLORSPACE_SRGB |
8 | [?] | x = 0.640, y = 0.330 | x = 0.300, y = 0.600 | x = 0.150, y = 0.060 | x = 0.3127, y = 0.3290, Illuminant D65 | E' = 4.5 I for I ≤0.018,1.099 I0.45 - 0.099 for 0.018 < I | n/a | ||
Notes: a. The coordinates of the color primaries aregiven in the CIE system (1931) b. The ubiquitous Bt878 video capture chipquantizes E'Y to 238 levels, yielding a rangeof Y' = 16 … 253, unlike Rec. 601 Y' = 16 …235. This is not a typo in the Bt878 documentation, it has beenimplemented in silicon. The chroma extents are unclear. c. No identifier exists for M/PAL which usesthe chromaticities of M/NTSC, the remaining parameters are equal to B andG/PAL. d. Note JFIF quantizesY'PBPR in range [0;+1] and[-0.5;+0.5] to257 levels, however Y'CbCr signalsare still clamped to [0;255]. |
2.3. Indexed Format
In this format each pixel is represented by an 8 bit indexinto a 256 entry ARGB palette. It is intended forVideo Output Overlays only. There are no ioctls toaccess the palette, this must be done with ioctls of the Linux framebuffer API.
2.4. RGB Formats
- Table of Contents
- Packed RGB formats -- Packed RGB formats
- V4L2_PIX_FMT_SBGGR8 ('BA81') -- Bayer RGB format
- V4L2_PIX_FMT_SBGGR16 ('BA82') -- Bayer RGB format
Packed RGB formats
Description
These formats are designed to match the pixel formats oftypical PC graphics frame buffers. They occupy 8, 16, 24 or 32 bitsper pixel. These are all packed-pixel formats, meaning all the datafor a pixel lie next to each other in memory.
When one of these formats is used, drivers shall report thecolorspace V4L2_COLORSPACE_SRGB
.
Table 2-1. Packed RGB Image Formats
Identifier | Code | Byte 0 in memory | Byte 1 | Byte 2 | Byte 3 | ||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||||
V4L2_PIX_FMT_RGB332 |
'RGB1' | b1 | b0 | g2 | g1 | g0 | r2 | r1 | r0 | ||||||||||||||||||||||||||||
V4L2_PIX_FMT_RGB444 |
'R444' | g3 | g2 | g1 | g0 | b3 | b2 | b1 | b0 | a3 | a2 | a1 | a0 | r3 | r2 | r1 | r0 | ||||||||||||||||||||
V4L2_PIX_FMT_RGB555 |
'RGBO' | g2 | g1 | g0 | r4 | r3 | r2 | r1 | r0 | a | b4 | b3 | b2 | b1 | b0 | g4 | g3 | ||||||||||||||||||||
V4L2_PIX_FMT_RGB565 |
'RGBP' | g2 | g1 | g0 | r4 | r3 | r2 | r1 | r0 | b4 | b3 | b2 | b1 | b0 | g5 | g4 | g3 | ||||||||||||||||||||
V4L2_PIX_FMT_RGB555X |
'RGBQ' | a | b4 | b3 | b2 | b1 | b0 | g4 | g3 | g2 | g1 | g0 | r4 | r3 | r2 | r1 | r0 | ||||||||||||||||||||
V4L2_PIX_FMT_RGB565X |
'RGBR' | b4 | b3 | b2 | b1 | b0 | g5 | g4 | g3 | g2 | g1 | g0 | r4 | r3 | r2 | r1 | r0 | ||||||||||||||||||||
V4L2_PIX_FMT_BGR24 |
'BGR3' | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | g7 | g6 | g5 | g4 | g3 | g2 | g1 | g0 | r7 | r6 | r5 | r4 | r3 | r2 | r1 | r0 | ||||||||||||
V4L2_PIX_FMT_RGB24 |
'RGB3' | r7 | r6 | r5 | r4 | r3 | r2 | r1 | r0 | g7 | g6 | g5 | g4 | g3 | g2 | g1 | g0 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | ||||||||||||
V4L2_PIX_FMT_BGR32 |
'BGR4' | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | g7 | g6 | g5 | g4 | g3 | g2 | g1 | g0 | r7 | r6 | r5 | r4 | r3 | r2 | r1 | r0 | a7 | a6 | a5 | a4 | a3 | a2 | a1 | a0 | ||||
V4L2_PIX_FMT_RGB32 |
'RGB4' | r7 | r6 | r5 | r4 | r3 | r2 | r1 | r0 | g7 | g6 | g5 | g4 | g3 | g2 | g1 | g0 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | a7 | a6 | a5 | a4 | a3 | a2 | a1 | a0 |
Bit 7 is the most significant bit. The value of a = alphabits is undefined when reading from the driver, ignored when writingto the driver, except when alpha blending has been negotiated for aVideo Overlay or Video Output Overlay.
Important: Drivers may interpret these formats differently.
Some RGB formats above are uncommon and were probablydefined in error. Drivers may interpret them as inTable 2-2.
Table 2-2. Packed RGB Image Formats (corrected)
Identifier | Code | Byte 0 in memory | Byte 1 | Byte 2 | Byte 3 | ||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||||
V4L2_PIX_FMT_RGB332 |
'RGB1' | r2 | r1 | r0 | g2 | g1 | g0 | b1 | b0 | ||||||||||||||||||||||||||||
V4L2_PIX_FMT_RGB444 |
'R444' | g3 | g2 | g1 | g0 | b3 | b2 | b1 | b0 | a3 | a2 | a1 | a0 | r3 | r2 | r1 | r0 | ||||||||||||||||||||
V4L2_PIX_FMT_RGB555 |
'RGBO' | g2 | g1 | g0 | b4 | b3 | b2 | b1 | b0 | a | r4 | r3 | r2 | r1 | r0 | g4 | g3 | ||||||||||||||||||||
V4L2_PIX_FMT_RGB565 |
'RGBP' | g2 | g1 | g0 | b4 | b3 | b2 | b1 | b0 | r4 | r3 | r2 | r1 | r0 | g5 | g4 | g3 | ||||||||||||||||||||
V4L2_PIX_FMT_RGB555X |
'RGBQ' | a | r4 | r3 | r2 | r1 | r0 | g4 | g3 | g2 | g1 | g0 | b4 | b3 | b2 | b1 | b0 | ||||||||||||||||||||
V4L2_PIX_FMT_RGB565X |
'RGBR' | r4 | r3 | r2 | r1 | r0 | g5 | g4 | g3 | g2 | g1 | g0 | b4 | b3 | b2 | b1 | b0 | ||||||||||||||||||||
V4L2_PIX_FMT_BGR24 |
'BGR3' | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | g7 | g6 | g5 | g4 | g3 | g2 | g1 | g0 | r7 | r6 | r5 | r4 | r3 | r2 | r1 | r0 | ||||||||||||
V4L2_PIX_FMT_RGB24 |
'RGB3' | r7 | r6 | r5 | r4 | r3 | r2 | r1 | r0 | g7 | g6 | g5 | g4 | g3 | g2 | g1 | g0 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | ||||||||||||
V4L2_PIX_FMT_BGR32 |
'BGR4' | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 | g7 | g6 | g5 | g4 | g3 | g2 | g1 | g0 | r7 | r6 | r5 | r4 | r3 | r2 | r1 | r0 | a7 | a6 | a5 | a4 | a3 | a2 | a1 | a0 | ||||
V4L2_PIX_FMT_RGB32 |
'RGB4' | a7 | a6 | a5 | a4 | a3 | a2 | a1 | a0 | r7 | r6 | r5 | r4 | r3 | r2 | r1 | r0 | g7 | g6 | g5 | g4 | g3 | g2 | g1 | g0 | b7 | b6 | b5 | b4 | b3 | b2 | b1 | b0 |
A test utility to determine which RGB formats a driveractually supports is available from the LinuxTV v4l-dvb repository.Seehttp://linuxtv.org/repo/ for access instructions.
V4L2_PIX_FMT_SBGGR8 ('BA81')
Description
This is commonly the native format of digital cameras,reflecting the arrangement of sensors on the CCD device. Only one red,green or blue value is given for each pixel. Missing components mustbe interpolated from neighbouring pixels. From left to right the firstrow consists of a blue and green value, the second row of a green andred value. This scheme repeats to the right and down for every twocolumns and rows.
V4L2_PIX_FMT_SBGGR16 ('BA82')
Description
This format is similar to V4L2_PIX_FMT_SBGGR8
, except each pixel hasa depth of 16 bits. The least significant byte is stored at lowermemory addresses (little-endian). Note the actual sampling precisionmay be lower than 16 bits, for example 10 bits per pixel with valuesin range 0 to 1023.
2.5. YUV Formats
- Table of Contents
- Packed YUV formats -- Packed YUV formats
- V4L2_PIX_FMT_GREY ('GREY') -- Grey-scale image
- V4L2_PIX_FMT_Y16 ('Y16 ') -- Grey-scale image
- V4L2_PIX_FMT_YUYV ('YUYV') -- Packed format with ½ horizontal chromaresolution, also known as YUV 4:2:2
-
V4L2_PIX_FMT_UYVY ('UYVY') -- Variation of
V4L2_PIX_FMT_YUYV
with different order of samplesin memory - V4L2_PIX_FMT_Y41P ('Y41P') -- Format with ¼ horizontal chromaresolution, also known as YUV 4:1:1
- V4L2_PIX_FMT_YVU420 ('YV12'), V4L2_PIX_FMT_YUV420 ('YU12') -- Planar formats with ½ horizontal andvertical chroma resolution, also known as YUV 4:2:0
- V4L2_PIX_FMT_YVU410 ('YVU9'), V4L2_PIX_FMT_YUV410 ('YUV9') -- Planar formats with ¼ horizontal andvertical chroma resolution, also known as YUV 4:1:0
-
V4L2_PIX_FMT_YUV422P ('422P') -- Format with ½ horizontal chroma resolution,also known as YUV 4:2:2. Planar layout as opposed to
V4L2_PIX_FMT_YUYV
-
V4L2_PIX_FMT_YUV411P ('411P') -- Format with ¼ horizontal chroma resolution,also known as YUV 4:1:1. Planar layout as opposed to
V4L2_PIX_FMT_Y41P
-
V4L2_PIX_FMT_NV12 ('NV12'), V4L2_PIX_FMT_NV21 ('NV21') -- Formats with ½ horizontal and verticalchroma resolution, also known as YUV 4:2:0. One luminance and onechrominance plane with alternating chroma samples as opposed to
V4L2_PIX_FMT_YVU420
YUV is the format native to TV broadcast and composite videosignals. It separates the brightness information (Y) from the colorinformation (U and V or Cb and Cr). The color information consists ofred and bluecolor difference signals, this waythe green component can be reconstructed by subtracting from thebrightness component. SeeSection 2.2 for conversionexamples. YUV was chosen because early television would only transmitbrightness information. To add color in a way compatible with existingreceivers a new signal carrier was added to transmit the colordifference signals. Secondary in the YUV format the U and V componentsusually have lower resolution than the Y component. This is an analogvideo compression technique taking advantage of a property of thehuman visual system, being more sensitive to brightnessinformation.
Packed YUV formats
Description
Similar to the packed RGB formats these formats storethe Y, Cb and Cr component of each pixel in one 16 or 32 bitword.
Table 2-1. Packed YUV Image Formats
Identifier | Code | Byte 0 in memory | Byte 1 | Byte 2 | Byte 3 | ||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Bit | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |||||
V4L2_PIX_FMT_YUV444 |
'Y444' | Cb3 | Cb2 | Cb1 | Cb0 | Cr3 | Cr2 | Cr1 | Cr0 | a3 | a2 | a1 | a0 | Y'3 | Y'2 | Y'1 | Y'0 | ||||||||||||||||||||
V4L2_PIX_FMT_YUV555 |
'YUVO' | Cb2 | Cb1 | Cb0 | Cr4 | Cr3 | Cr2 | Cr1 | Cr0 | a | Y'4 | Y'3 | Y'2 | Y'1 | Y'0 | Cb4 | Cb3 | ||||||||||||||||||||
V4L2_PIX_FMT_YUV565 |
'YUVP' | Cb2 | Cb1 | Cb0 | Cr4 | Cr3 | Cr2 | Cr1 | Cr0 | Y'4 | Y'3 | Y'2 | Y'1 | Y'0 | Cb5 | Cb4 | Cb3 | ||||||||||||||||||||
V4L2_PIX_FMT_YUV32 |
'YUV4' | a7 | a6 | a5 | a4 | a3 | a2 | a1 | a0 | Y'7 | Y'6 | Y'5 | Y'4 | Y'3 | Y'2 | Y'1 | Y'0 | Cb7 | Cb6 | Cb5 | Cb4 | Cb3 | Cb2 | Cb1 | Cb0 | Cr7 | Cr6 | Cr5 | Cr4 | Cr3 | Cr2 | Cr1 | Cr0 |
Bit 7 is the most significant bit. The value of a = alphabits is undefined when reading from the driver, ignored when writingto the driver, except when alpha blending has been negotiated for aVideo Overlay or Video Output Overlay.
V4L2_PIX_FMT_GREY ('GREY')
Description
This is a grey-scale image. It is really a degenerateY'CbCr format which simply contains no Cb or Cr data.
V4L2_PIX_FMT_Y16 ('Y16 ')
Description
This is a grey-scale image with a depth of 16 bits perpixel. The least significant byte is stored at lower memory addresses(little-endian). Note the actual sampling precision may be lower than16 bits, for example 10 bits per pixel with values in range 0 to1023.
Example 2-1. V4L2_PIX_FMT_Y16
4 × 4pixel image
Byte Order. Each cell is one byte.
start + 0: | Y'00low | Y'00high | Y'01low | Y'01high | Y'02low | Y'02high | Y'03low | Y'03high |
start + 8: | Y'10low | Y'10high | Y'11low | Y'11high | Y'12low | Y'12high | Y'13low | Y'13high |
start + 16: | Y'20low | Y'20high | Y'21low | Y'21high | Y'22low | Y'22high | Y'23low | Y'23high |
start + 24: | Y'30low | Y'30high | Y'31low | Y'31high | Y'32low | Y'32high | Y'33low | Y'33high |
V4L2_PIX_FMT_YUYV ('YUYV')
Description
In this format each four bytes is two pixels. Each fourbytes is two Y's, a Cb and a Cr. Each Y goes to one of the pixels, andthe Cb and Cr belong to both pixels. As you can see, the Cr and Cbcomponents have half the horizontal resolution of the Y component.V4L2_PIX_FMT_YUYV
is known in the Windowsenvironment as YUY2.
V4L2_PIX_FMT_UYVY ('UYVY')
Description
In this format each four bytes is two pixels. Each fourbytes is two Y's, a Cb and a Cr. Each Y goes to one of the pixels, andthe Cb and Cr belong to both pixels. As you can see, the Cr and Cbcomponents have half the horizontal resolution of the Ycomponent.
V4L2_PIX_FMT_Y41P ('Y41P')
Description
In this format each 12 bytes is eight pixels. In thetwelve bytes are two CbCr pairs and eight Y's. The first CbCr pairgoes with the first four Y's, and the second CbCr pair goes with theother four Y's. The Cb and Cr components have one fourth thehorizontal resolution of the Y component.
Do not confuse this format with V4L2_PIX_FMT_YUV411P
. Y41P is derived from "YUV 4:1:1packed", whileYUV411P stands for "YUV 4:1:1planar".
V4L2_PIX_FMT_YVU420 ('YV12'), V4L2_PIX_FMT_YUV420 ('YU12')
Name
V4L2_PIX_FMT_YVU420
,
V4L2_PIX_FMT_YUV420
-- Planar formats with ½ horizontal andvertical chroma resolution, also known as YUV 4:2:0
Description
These are planar formats, as opposed to a packed format.The three components are separated into three sub- images or planes.The Y plane is first. The Y plane has one byte per pixel. ForV4L2_PIX_FMT_YVU420
, the Cr plane immediatelyfollows the Y plane in memory. The Cr plane is half the width and halfthe height of the Y plane (and of the image). Each Cr belongs to fourpixels, a two-by-two square of the image. For example,Cr0 belongs to Y'00,Y'01, Y'10, andY'11. Following the Cr plane is the Cb plane,just like the Cr plane.V4L2_PIX_FMT_YUV420
isthe same except the Cb plane comes first, then the Cr plane.
If the Y plane has pad bytes after each row, then the Crand Cb planes have half as many pad bytes after their rows. In otherwords, two Cx rows (including padding) is exactly as long as one Y row(including padding).
V4L2_PIX_FMT_YVU410 ('YVU9'), V4L2_PIX_FMT_YUV410 ('YUV9')
Name
V4L2_PIX_FMT_YVU410
,
V4L2_PIX_FMT_YUV410
-- Planar formats with ¼ horizontal andvertical chroma resolution, also known as YUV 4:1:0
Description
These are planar formats, as opposed to a packed format.The three components are separated into three sub-images or planes.The Y plane is first. The Y plane has one byte per pixel. ForV4L2_PIX_FMT_YVU410
, the Cr plane immediatelyfollows the Y plane in memory. The Cr plane is ¼ the width and¼ the height of the Y plane (and of the image). Each Cr belongsto 16 pixels, a four-by-four square of the image. Following the Crplane is the Cb plane, just like the Cr plane.V4L2_PIX_FMT_YUV410
is the same, except the Cbplane comes first, then the Cr plane.
If the Y plane has pad bytes after each row, then the Crand Cb planes have ¼ as many pad bytes after their rows. Inother words, four Cx rows (including padding) are exactly as long asone Y row (including padding).
V4L2_PIX_FMT_YUV422P ('422P')
Name
V4L2_PIX_FMT_YUV422P
-- Format with ½ horizontal chroma resolution,also known as YUV 4:2:2. Planar layout as opposed to
V4L2_PIX_FMT_YUYV
Description
This format is not commonly used. This is a planarversion of the YUYV format. The three components are separated intothree sub-images or planes. The Y plane is first. The Y plane has onebyte per pixel. The Cb plane immediately follows the Y plane inmemory. The Cb plane is half the width of the Y plane (and of theimage). Each Cb belongs to two pixels. For example,Cb0 belongs to Y'00,Y'01. Following the Cb plane is the Cr plane,just like the Cb plane.
If the Y plane has pad bytes after each row, then the Crand Cb planes have half as many pad bytes after their rows. In otherwords, two Cx rows (including padding) is exactly as long as one Y row(including padding).
Example 2-1. V4L2_PIX_FMT_YUV422P
4 × 4pixel image
Byte Order. Each cell is one byte.
start + 0: | Y'00 | Y'01 | Y'02 | Y'03 |
start + 4: | Y'10 | Y'11 | Y'12 | Y'13 |
start + 8: | Y'20 | Y'21 | Y'22 | Y'23 |
start + 12: | Y'30 | Y'31 | Y'32 | Y'33 |
start + 16: | Cb00 | Cb01 | ||
start + 18: | Cb10 | Cb11 | ||
start + 20: | Cb20 | Cb21 | ||
start + 22: | Cb30 | Cb31 | ||
start + 24: | Cr00 | Cr01 | ||
start + 26: | Cr10 | Cr11 | ||
start + 28: | Cr20 | Cr21 | ||
start + 30: | Cr30 | Cr31 |
V4L2_PIX_FMT_YUV411P ('411P')
Name
V4L2_PIX_FMT_YUV411P
-- Format with ¼ horizontal chroma resolution,also known as YUV 4:1:1. Planar layout as opposed to
V4L2_PIX_FMT_Y41P
Description
This format is not commonly used. This is a planarformat similar to the 4:2:2 planar format except with half as manychroma. The three components are separated into three sub-images orplanes. The Y plane is first. The Y plane has one byte per pixel. TheCb plane immediately follows the Y plane in memory. The Cb plane is¼ the width of the Y plane (and of the image). Each Cb belongsto 4 pixels all on the same row. For example,Cb0 belongs to Y'00,Y'01, Y'02 andY'03. Following the Cb plane is the Cr plane,just like the Cb plane.
If the Y plane has pad bytes after each row, then the Crand Cb planes have ¼ as many pad bytes after their rows. Inother words, four C x rows (including padding) is exactly as long asone Y row (including padding).
V4L2_PIX_FMT_NV12 ('NV12'), V4L2_PIX_FMT_NV21 ('NV21')
Name
V4L2_PIX_FMT_NV12
,
V4L2_PIX_FMT_NV21
-- Formats with ½ horizontal and verticalchroma resolution, also known as YUV 4:2:0. One luminance and onechrominance plane with alternating chroma samples as opposed to
V4L2_PIX_FMT_YVU420
Description
These are two-plane versions of the YUV 4:2:0 format.The three components are separated into two sub-images or planes. TheY plane is first. The Y plane has one byte per pixel. ForV4L2_PIX_FMT_NV12
, a combined CbCr planeimmediately follows the Y plane in memory. The CbCr plane is the samewidth, in bytes, as the Y plane (and of the image), but is half astall in pixels. Each CbCr pair belongs to four pixels. For example,Cb0/Cr0 belongs toY'00, Y'01,Y'10, Y'11.V4L2_PIX_FMT_NV21
is the same except the Cb andCr bytes are swapped, the CrCb plane starts with a Cr byte.
If the Y plane has pad bytes after each row, then theCbCr plane has as many pad bytes after its rows.
2.6. Compressed Formats
Table 2-7. Compressed Image Formats
Identifier | Code | Details |
---|---|---|
V4L2_PIX_FMT_JPEG |
'JPEG' | TBD. See also VIDIOC_G_JPEGCOMP , VIDIOC_S_JPEGCOMP . |
V4L2_PIX_FMT_MPEG |
'MPEG' | MPEG stream. The actual format is determined byextended control V4L2_CID_MPEG_STREAM_TYPE , seeTable 1-2. |
2.7. Reserved Format Identifiers
These formats are not defined by this specification, theyare just listed for reference and to avoid naming conflicts. If youwant to register your own format, send an e-mail to the V4L mailinglisthttps://listman.redhat.com/mailman/listinfo/video4linux-list for inclusion in thevideodev.hfile. If you want to share your format with other developers add alink to your documentation and send a copy to the maintainer of thisdocument, Michael Schimek<mschimek@gmx.at>
, forinclusion in this section. If you think your format should be listedin a standard format section please make a proposal on the V4L mailinglist.
Table 2-8. Reserved Image Formats
Identifier | Code | Details |
---|---|---|
V4L2_PIX_FMT_DV |
'dvsd' | unknown |
V4L2_PIX_FMT_ET61X251 |
'E625' | Compressed format of the ET61X251 driver. |
V4L2_PIX_FMT_HI240 |
'HI24' | 8 bit RGB format used by the BTTV driver,http://bytesex.org/bttv/ |
V4L2_PIX_FMT_HM12 |
'HM12' | YUV 4:2:0 format used by theIVTV driver, http://www.ivtvdriver.org/ The format is documented in thekernel sources in the file Documentation/video4linux/cx2341x/README.hm12 |
V4L2_PIX_FMT_MJPEG |
'MJPG' | Compressed format used by the Zoran driver |
V4L2_PIX_FMT_PWC1 |
'PWC1' | Compressed format of the PWC driver. |
V4L2_PIX_FMT_PWC2 |
'PWC2' | Compressed format of the PWC driver. |
V4L2_PIX_FMT_SN9C10X |
'S910' | Compressed format of the SN9C102 driver. |
V4L2_PIX_FMT_WNVA |
'WNVA' | Used by the Winnov Videum driver, http://www.thedirks.org/winnov/ |
V4L2_PIX_FMT_YYUV |
'YYUV' | unknown |
Chapter 3. Input/Output
The V4L2 API defines several different methods to read from orwrite to a device. All drivers exchanging data with applications mustsupport at least one of them.
The classic I/O method using the read()
and write()
function is automatically selectedafter opening a V4L2 device. When the driver does not support thismethod attempts to read or write will fail at any time.
Other methods must be negotiated. To select the streaming I/Omethod with memory mapped or user buffers applications call theVIDIOC_REQBUFS
ioctl. The asynchronous I/O method is not definedyet.
Video overlay can be considered another I/O method, althoughthe application does not directly receive the image data. It isselected by initiating video overlay with theVIDIOC_S_FMT
ioctl.For more information seeSection 4.2.
Generally exactly one I/O method, including overlay, isassociated with each file descriptor. The only exceptions areapplications not exchanging data with a driver ("panel applications",seeSection 1.1) and drivers permitting simultaneous video capturingand overlay using the same file descriptor, for compatibility with V4Land earlier versions of V4L2.
VIDIOC_S_FMT
andVIDIOC_REQBUFS
would permit this to some degree,but for simplicity drivers need not support switching the I/O method(after first switching away from read/write) other than by closingand reopening the device.
The following sections describe the various I/O methods inmore detail.
3.1. Read/Write
Input and output devices support theread()
and write()
function,respectively, when the V4L2_CAP_READWRITE
flag inthecapabilities
field of struct v4l2_capabilityreturned by theVIDIOC_QUERYCAP
ioctl is set.
Drivers may need the CPU to copy the data, but they may alsosupport DMA to or from user memory, so this I/O method is notnecessarily less efficient than other methods merely exchanging bufferpointers. It is considered inferior though because no meta-informationlike frame counters or timestamps are passed. This information isnecessary to recognize frame dropping and to synchronize with otherdata streams. However this is also the simplest I/O method, requiringlittle or no setup to exchange data. It permits command line stuntslike this (the vidctrl tool isfictitious):
> vidctrl /dev/video --input=0 --format=YUYV --size=352x288 > dd if=/dev/video of=myimage.422 bs=202752 count=1
To read from the device applications use theread()
function, to write thewrite()
function.Drivers must implement one I/O method if theyexchange data with applications, but it need not be this.[12] When reading or writing is supported, the drivermust also support the select()
and poll()
function.[13]
3.2. Streaming I/O (Memory Mapping)
Input and output devices support this I/O method when theV4L2_CAP_STREAMING
flag in thecapabilities
field of struct v4l2_capabilityreturned by the VIDIOC_QUERYCAP
ioctl is set. There are twostreaming methods, to determine if the memory mapping flavor issupported applications must call theVIDIOC_REQBUFS
ioctl.
Streaming is an I/O method where only pointers to buffersare exchanged between application and driver, the data itself is notcopied. Memory mapping is primarily intended to map buffers in devicememory into the application's address space. Device memory can be forexample the video memory on a graphics card with a video captureadd-on. However, being the most efficient I/O method available for along time, many other drivers support streaming as well, allocatingbuffers in DMA-able main memory.
A driver can support many sets of buffers. Each set isidentified by a unique buffer type value. The sets are independent andeach set can hold a different type of data. To access different setsat the same time different file descriptors must be used.[14]
To allocate device buffers applications call theVIDIOC_REQBUFS
ioctl with the desired number of buffers and buffertype, for exampleV4L2_BUF_TYPE_VIDEO_CAPTURE
.This ioctl can also be used to change the number of buffers or to freethe allocated memory, provided none of the buffers are stillmapped.
Before applications can access the buffers they must mapthem into their address space with themmap()
function. Thelocation of the buffers in device memory can be determined with theVIDIOC_QUERYBUF
ioctl. Them.offset
andlength
returned in a struct v4l2_buffer arepassed as sixth and second parameter to themmap()
function. The offset and length valuesmust not be modified. Remember the buffers are allocated in physicalmemory, as opposed to virtual memory which can be swapped out to disk.Applications should free the buffers as soon as possible with themunmap()
function.
Example 3-1. Mapping buffers
struct v4l2_requestbuffers reqbuf; struct { void *start; size_t length; } *buffers; unsigned int i; memset (&reqbuf, 0, sizeof (reqbuf)); reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; reqbuf.memory = V4L2_MEMORY_MMAP; reqbuf.count = 20; if (-1 == ioctl (fd,VIDIOC_REQBUFS
, &reqbuf)) { if (errno == EINVAL) printf ("Video capturing or mmap-streaming is not supported\n"); else perror ("VIDIOC_REQBUFS"); exit (EXIT_FAILURE); } /* We want at least five buffers. */ if (reqbuf.count < 5) { /* You may need to free the buffers here. */ printf ("Not enough buffer memory\n"); exit (EXIT_FAILURE); } buffers = calloc (reqbuf.count, sizeof (*buffers)); assert (buffers != NULL); for (i = 0; i < reqbuf.count; i++) { struct v4l2_buffer buffer; memset (&buffer, 0, sizeof (buffer)); buffer.type = reqbuf.type; buffer.memory = V4L2_MEMORY_MMAP; buffer.index = i; if (-1 == ioctl (fd,VIDIOC_QUERYBUF
, &buffer)) { perror ("VIDIOC_QUERYBUF"); exit (EXIT_FAILURE); } buffers[i].length = buffer.length; /* remember for munmap() */ buffers[i].start = mmap (NULL, buffer.length, PROT_READ | PROT_WRITE, /* recommended */ MAP_SHARED, /* recommended */ fd, buffer.m.offset); if (MAP_FAILED == buffers[i].start) { /* If you do not exit here you should unmap() and free() the buffers mapped so far. */ perror ("mmap"); exit (EXIT_FAILURE); } } /* Cleanup. */ for (i = 0; i < reqbuf.count; i++) munmap (buffers[i].start, buffers[i].length);
Conceptually streaming drivers maintain two buffer queues, an incomingand an outgoing queue. They separate the synchronous capture or outputoperation locked to a video clock from the application which issubject to random disk or network delays and preemption byother processes, thereby reducing the probability of data loss.The queues are organized as FIFOs, buffers will beoutput in the order enqueued in the incoming FIFO, and werecaptured in the order dequeued from the outgoing FIFO.
The driver may require a minimum number of buffers enqueuedat all times to function, apart of this no limit exists on the numberof buffers applications can enqueue in advance, or dequeue andprocess. They can also enqueue in a different order than buffers havebeen dequeued, and the driver can fill enqueuedempty buffers in any order.[15] The index number of a buffer (struct v4l2_bufferindex
) plays no role here, it onlyidentifies the buffer.
Initially all mapped buffers are in dequeued state,inaccessible by the driver. For capturing applications it is customaryto first enqueue all mapped buffers, then to start capturing and enterthe read loop. Here the application waits until a filled buffer can bedequeued, and re-enqueues the buffer when the data is no longerneeded. Output applications fill and enqueue buffers, when enoughbuffers are stacked up the output is started withVIDIOC_STREAMON
. In the write loop, whenthe application runs out of free buffers, it must wait until an emptybuffer can be dequeued and reused.
To enqueue and dequeue a buffer applications use theVIDIOC_QBUF
andVIDIOC_DQBUF
ioctl. The status of a buffer beingmapped, enqueued, full or empty can be determined at any time using theVIDIOC_QUERYBUF
ioctl. Two methods exist to suspend execution of theapplication until one or more buffers can be dequeued. By defaultVIDIOC_DQBUF
blocks when no buffer is in theoutgoing queue. When theO_NONBLOCK
flag wasgiven to theopen()
function,VIDIOC_DQBUF
returns immediately with anEAGAIN error code when no buffer is available. Theselect()
orpoll()
function are always available.
To start and stop capturing or output applications call theVIDIOC_STREAMON
andVIDIOC_STREAMOFF
ioctl. NoteVIDIOC_STREAMOFF
removes all buffers from bothqueues as a side effect. Since there is no notion of doing anything"now" on a multitasking system, if an application needs to synchronizewith another event it should examine the struct v4l2_buffertimestamp
of captured buffers, or set thefield before enqueuing buffers for output.
Drivers implementing memory mapping I/O mustsupport the VIDIOC_REQBUFS
,VIDIOC_QUERYBUF
,VIDIOC_QBUF
,VIDIOC_DQBUF
,VIDIOC_STREAMON
andVIDIOC_STREAMOFF
ioctl, themmap()
,munmap()
,select()
andpoll()
function.[16]
[capture example]
3.3. Streaming I/O (User Pointers)
Input and output devices support this I/O method when theV4L2_CAP_STREAMING
flag in thecapabilities
field of struct v4l2_capabilityreturned by the VIDIOC_QUERYCAP
ioctl is set. If the particular userpointer method (not only memory mapping) is supported must bedetermined by calling theVIDIOC_REQBUFS
ioctl.
This I/O method combines advantages of the read/write andmemory mapping methods. Buffers are allocated by the applicationitself, and can reside for example in virtual or shared memory. Onlypointers to data are exchanged, these pointers and meta-informationare passed in struct v4l2_buffer. The driver must be switchedinto user pointer I/O mode by calling theVIDIOC_REQBUFS
with thedesired buffer type. No buffers are allocated beforehands,consequently they are not indexed and cannot be queried like mappedbuffers with theVIDIOC_QUERYBUF
ioctl.
Example 3-2. Initiating streaming I/O with user pointers
struct v4l2_requestbuffers reqbuf;
memset (&reqbuf, 0, sizeof (reqbuf));
reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
reqbuf.memory = V4L2_MEMORY_USERPTR;
if (ioctl (fd, VIDIOC_REQBUFS
, &reqbuf) == -1) {
if (errno == EINVAL)
printf ("Video capturing or user pointer streaming is not supported\n");
else
perror ("VIDIOC_REQBUFS");
exit (EXIT_FAILURE);
}
Buffer addresses and sizes are passed on the fly with theVIDIOC_QBUF
ioctl. Although buffers are commonly cycled,applications can pass different addresses and sizes at eachVIDIOC_QBUF
call. If required by the hardware thedriver swaps memory pages within physical memory to create acontinuous area of memory. This happens transparently to theapplication in the virtual memory subsystem of the kernel. When bufferpages have been swapped out to disk they are brought back and finallylocked in physical memory for DMA.[17]
Filled or displayed buffers are dequeued with theVIDIOC_DQBUF
ioctl. The driver can unlock the memory pages at anytime between the completion of the DMA and this ioctl. The memory isalso unlocked when VIDIOC_STREAMOFF
is called, VIDIOC_REQBUFS
, orwhen the device is closed. Applications must take care not to freebuffers without dequeuing. For once, the buffers remain locked untilfurther, wasting physical memory. Second the driver will not benotified when the memory is returned to the application's free listand subsequently reused for other purposes, possibly completing therequested DMA and overwriting valuable data.
For capturing applications it is customary to enqueue anumber of empty buffers, to start capturing and enter the read loop.Here the application waits until a filled buffer can be dequeued, andre-enqueues the buffer when the data is no longer needed. Outputapplications fill and enqueue buffers, when enough buffers are stackedup output is started. In the write loop, when the applicationruns out of free buffers it must wait until an empty buffer can bedequeued and reused. Two methods exist to suspend execution of theapplication until one or more buffers can be dequeued. By defaultVIDIOC_DQBUF
blocks when no buffer is in theoutgoing queue. When theO_NONBLOCK
flag wasgiven to theopen()
function,VIDIOC_DQBUF
returns immediately with anEAGAIN error code when no buffer is available. Theselect()
orpoll()
function are always available.
To start and stop capturing or output applications call theVIDIOC_STREAMON
andVIDIOC_STREAMOFF
ioctl. NoteVIDIOC_STREAMOFF
removes all buffers from bothqueues and unlocks all buffers as a side effect. Since there is nonotion of doing anything "now" on a multitasking system, if anapplication needs to synchronize with another event it should examinethe struct v4l2_buffertimestamp
of capturedbuffers, or set the field before enqueuing buffers for output.
Drivers implementing user pointer I/O mustsupport the VIDIOC_REQBUFS
,VIDIOC_QBUF
,VIDIOC_DQBUF
,VIDIOC_STREAMON
andVIDIOC_STREAMOFF
ioctl, theselect()
andpoll()
function.[18]
3.5. Buffers
A buffer contains data exchanged by application anddriver using one of the Streaming I/O methods. Only pointers tobuffers are exchanged, the data itself is not copied. These pointers,together with meta-information like timestamps or field parity, arestored in a struct v4l2_buffer
, argument tothe VIDIOC_QUERYBUF
, VIDIOC_QBUF
and VIDIOC_DQBUF
ioctl.
Nominally timestamps refer to the first data byte transmitted.In practice however the wide range of hardware covered by the V4L2 APIlimits timestamp accuracy. Often an interrupt routine willsample the system clock shortly after the field or frame was storedcompletely in memory. So applications must expect a constantdifference up to one field or frame period plus a small (few scanlines) random error. The delay and error can be muchlarger due to compression or transmission over an external bus whenthe frames are not properly stamped by the sender. This is frequentlythe case with USB cameras. Here timestamps refer to the instant thefield or frame was received by the driver, not the capture time. Thesedevices identify by not enumerating any video standards, seeSection 1.7.
Similar limitations apply to output timestamps. Typicallythe video hardware locks to a clock controlling the video timing, thehorizontal and vertical synchronization pulses. At some point in theline sequence, possibly the vertical blanking, an interrupt routinesamples the system clock, compares against the timestamp and programsthe hardware to repeat the previous field or frame, or to display thebuffer contents.
Apart of limitations of the video device and naturalinaccuracies of all clocks, it should be noted system time itself isnot perfectly stable. It can be affected by power saving cycles,warped to insert leap seconds, or even turned back or forth by thesystem administrator affecting long term measurements. [19]
Table 3-1. struct v4l2_buffer
__u32 | index |
Number of the buffer, set by the application. Thisfield is only used for memory mapping I/Oand can range from zero to the number of buffers allocatedwith theVIDIOC_REQBUFS ioctl (struct v4l2_requestbufferscount ) minus one. |
|
enum v4l2_buf_type | type |
Type of the buffer, same as struct v4l2_formattype or struct v4l2_requestbufferstype , set by the application. |
|
__u32 | bytesused |
The number of bytes occupied by the data in thebuffer. It depends on the negotiated data format and may change witheach buffer for compressed variable size data like JPEG images.Drivers must set this field whentype refers to an input stream, applications when an output stream. |
|
__u32 | flags |
Flags set by the application or driver, see Table 3-3. | |
enum v4l2_field | field |
Indicates the field order of the image in thebuffer, see Table 3-8. This field is not used whenthe buffer contains VBI data. Drivers must set it whentype refers to an input stream,applications when an output stream. |
|
struct timeval | timestamp |
For input streams this is thesystem time (as returned by the |
|
struct v4l2_timecode | timecode |
When type isV4L2_BUF_TYPE_VIDEO_CAPTURE and theV4L2_BUF_FLAG_TIMECODE flag is set inflags , this structure contains a frametimecode. In V4L2_FIELD_ALTERNATEmode the top and bottom field contain the same timecode.Timecodes are intended to help video editing and are typically recorded onvideo tapes, but also embedded in compressed formats like MPEG. Thisfield is independent of the timestamp andsequence fields. |
|
__u32 | sequence |
Set by the driver, counting the frames in thesequence. | |
In V4L2_FIELD_ALTERNATE mode the top andbottom field have the same sequence number. The count starts at zeroand includes dropped or repeated frames. A dropped frame was receivedby an input device but could not be stored due to lack of free bufferspace. A repeated frame was displayed again by an output devicebecause the application did not pass new data intime. Note this may count the frames receivede.g. over USB, without taking into account the frames dropped by theremote hardware due to limited compression throughput or busbandwidth. These devices identify by not enumerating any videostandards, seeSection 1.7. |
|||
enum v4l2_memory | memory |
This field must be set by applications and/or driversin accordance with the selected I/O method. | |
union | m |
||
__u32 | offset |
When memory isV4L2_MEMORY_MMAP this is the offset of the bufferfrom the start of the device memory. The value is returned by thedriver and apart of serving as parameter to themmap() functionnot useful for applications. SeeSection 3.2 for details. |
|
unsigned long | userptr |
When memory isV4L2_MEMORY_USERPTR this is a pointer to thebuffer (casted to unsigned long type) in virtual memory, set by theapplication. SeeSection 3.3 for details. |
|
__u32 | length |
Size of the buffer (not the payload) in bytes. | |
__u32 | input |
Some video capture drivers support rapid andsynchronous video input changes, a function useful for example invideo surveillance applications. For this purpose applications set theV4L2_BUF_FLAG_INPUT flag, and this field to thenumber of a video input as in struct v4l2_input fieldindex . |
|
__u32 | reserved |
A place holder for future extensions and custom(driver defined) buffer typesV4L2_BUF_TYPE_PRIVATE and higher. |
Table 3-2. enum v4l2_buf_type
V4L2_BUF_TYPE_VIDEO_CAPTURE |
1 | Buffer of a video capture stream, see Section 4.1. |
V4L2_BUF_TYPE_VIDEO_OUTPUT |
2 | Buffer of a video output stream, see Section 4.3. |
V4L2_BUF_TYPE_VIDEO_OVERLAY |
3 | Buffer for video overlay, see Section 4.2. |
V4L2_BUF_TYPE_VBI_CAPTURE |
4 | Buffer of a raw VBI capture stream, see Section 4.7. |
V4L2_BUF_TYPE_VBI_OUTPUT |
5 | Buffer of a raw VBI output stream, see Section 4.7. |
V4L2_BUF_TYPE_SLICED_VBI_CAPTURE |
6 | Buffer of a sliced VBI capture stream, see Section 4.8. |
V4L2_BUF_TYPE_SLICED_VBI_OUTPUT |
7 | Buffer of a sliced VBI output stream, see Section 4.8. |
V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY |
8 | Buffer for video output overlay (OSD), see Section 4.4. Status: Experimental. |
V4L2_BUF_TYPE_PRIVATE |
0x80 | This and higher values are reserved for custom(driver defined) buffer types. |
Table 3-3. Buffer Flags
V4L2_BUF_FLAG_MAPPED |
0x0001 | The buffer resides in device memory and has been mappedinto the application's address space, seeSection 3.2 for details.Drivers set or clear this flag when theVIDIOC_QUERYBUF,VIDIOC_QBUF orVIDIOC_DQBUF ioctl is called. Set by the driver. |
V4L2_BUF_FLAG_QUEUED |
0x0002 | Internally drivers maintain two buffer queues, anincoming and outgoing queue. When this flag is set, the buffer iscurrently on the incoming queue. It automatically moves to theoutgoing queue after the buffer has been filled (capture devices) ordisplayed (output devices). Drivers set or clear this flag when theVIDIOC_QUERYBUF ioctl is called. After(successful) calling theVIDIOC_QBUF ioctl it isalways set and afterVIDIOC_DQBUF alwayscleared. |
V4L2_BUF_FLAG_DONE |
0x0004 | When this flag is set, the buffer is currently onthe outgoing queue, ready to be dequeued from the driver. Drivers setor clear this flag when theVIDIOC_QUERYBUF ioctlis called. After calling theVIDIOC_QBUF orVIDIOC_DQBUF it is always cleared. Of course abuffer cannot be on both queues at the same time, theV4L2_BUF_FLAG_QUEUED andV4L2_BUF_FLAG_DONE flag are mutually exclusive.They can be both cleared however, then the buffer is in "dequeued"state, in the application domain to say so. |
V4L2_BUF_FLAG_KEYFRAME |
0x0008 | Drivers set or clear this flag when calling theVIDIOC_DQBUF ioctl. It may be set by videocapture devices when the buffer contains a compressed image which is akey frame (or field), i. e. can be decompressed on its own. |
V4L2_BUF_FLAG_PFRAME |
0x0010 | Similar to V4L2_BUF_FLAG_KEYFRAME this flags predicted frames or fields which contain only differences to aprevious key frame. |
V4L2_BUF_FLAG_BFRAME |
0x0020 | Similar to V4L2_BUF_FLAG_PFRAME this is a bidirectional predicted frame or field. [ooc tbd] |
V4L2_BUF_FLAG_TIMECODE |
0x0100 | The timecode field is valid.Drivers set or clear this flag when theVIDIOC_DQBUF ioctl is called. |
V4L2_BUF_FLAG_INPUT |
0x0200 | The input field is valid.Applications set or clear this flag before calling theVIDIOC_QBUF ioctl. |
Table 3-4. enum v4l2_memory
V4L2_MEMORY_MMAP |
1 | The buffer is used for memorymapping I/O. |
V4L2_MEMORY_USERPTR |
2 | The buffer is used for userpointer I/O. |
V4L2_MEMORY_OVERLAY |
3 | [to do] |
3.5.1. Timecodes
The v4l2_timecode
structure isdesigned to hold aSMPTE 12M or similar timecode.(structtimeval
timestamps are stored instruct v4l2_buffer fieldtimestamp
.)
Table 3-5. struct v4l2_timecode
__u32 | type |
Frame rate the timecodes are based on, see Table 3-6. |
__u32 | flags |
Timecode flags, see Table 3-7. |
__u8 | frames |
Frame count, 0 ... 23/24/29/49/59, depending on the type of timecode. |
__u8 | seconds |
Seconds count, 0 ... 59. This is a binary, not BCD number. |
__u8 | minutes |
Minutes count, 0 ... 59. This is a binary, not BCD number. |
__u8 | hours |
Hours count, 0 ... 29. This is a binary, not BCD number. |
__u8 | userbits [4] |
The "user group" bits from the timecode. |
Table 3-6. Timecode Types
V4L2_TC_TYPE_24FPS |
1 | 24 frames per second, i. e. film. |
V4L2_TC_TYPE_25FPS |
2 | 25 frames per second, i. e. PAL or SECAM video. |
V4L2_TC_TYPE_30FPS |
3 | 30 frames per second, i. e. NTSC video. |
V4L2_TC_TYPE_50FPS |
4 | |
V4L2_TC_TYPE_60FPS |
5 |
Table 3-7. Timecode Flags
V4L2_TC_FLAG_DROPFRAME |
0x0001 | Indicates "drop frame" semantics for counting framesin 29.97 fps material. When set, frame numbers 0 and 1 at the start ofeach minute, except minutes 0, 10, 20, 30, 40, 50 are omitted from thecount. |
V4L2_TC_FLAG_COLORFRAME |
0x0002 | The "color frame" flag. |
V4L2_TC_USERBITS_field |
0x000C | Field mask for the "binary group flags". |
V4L2_TC_USERBITS_USERDEFINED |
0x0000 | Unspecified format. |
V4L2_TC_USERBITS_8BITCHARS |
0x0008 | 8-bit ISO characters. |
3.6. Field Order
We have to distinguish between progressive and interlacedvideo. Progressive video transmits all lines of a video imagesequentially. Interlaced video divides an image into two fields,containing only the odd and even lines of the image, respectively.Alternating the so called odd and even field are transmitted, and dueto a small delay between fields a cathode ray TV displays the linesinterleaved, yielding the original frame. This curious technique wasinvented because at refresh rates similar to film the image wouldfade out too quickly. Transmitting fields reduces the flicker withoutthe necessity of doubling the frame rate and with it the bandwidthrequired for each channel.
It is important to understand a video camera does not exposeone frame at a time, merely transmitting the frames separated intofields. The fields are in fact captured at two different instances intime. An object on screen may well move between one field and thenext. For applications analysing motion it is of paramount importanceto recognize which field of a frame is older, thetemporalorder.
When the driver provides or accepts images field by fieldrather than interleaved, it is also important applications understandhow the fields combine to frames. We distinguish between top andbottom fields, thespatial order: The first lineof the top field is the first line of an interlaced frame, the firstline of the bottom field is the second line of that frame.
However because fields were captured one after the other,arguing whether a frame commences with the top or bottom field ispointless. Any two successive top and bottom, or bottom and top fieldsyield a valid frame. Only when the source was progressive to beginwith, e. g. when transferring film to video, two fields may come fromthe same frame, creating a natural order.
Counter to intuition the top field is not necessarily theolder field. Whether the older field contains the top or bottom linesis a convention determined by the video standard. Hence thedistinction between temporal and spatial order of fields. The diagramsbelow should make this clearer.
All video capture and output devices must report the currentfield order. Some drivers may permit the selection of a differentorder, to this end applications initialize thefield
field of struct v4l2_pix_format beforecalling the VIDIOC_S_FMT
ioctl. If this is not desired it shouldhave the valueV4L2_FIELD_ANY
(0).
Table 3-8. enum v4l2_field
V4L2_FIELD_ANY |
0 | Applications request this field order when anyone of the V4L2_FIELD_NONE ,V4L2_FIELD_TOP ,V4L2_FIELD_BOTTOM , orV4L2_FIELD_INTERLACED formats is acceptable.Drivers choose depending on hardware capabilities or e. g. therequested image size, and return the actual field order. struct v4l2_bufferfield can never beV4L2_FIELD_ANY . |
V4L2_FIELD_NONE |
1 | Images are in progressive format, not interlaced.The driver may also indicate this order when it cannot distinguishbetweenV4L2_FIELD_TOP andV4L2_FIELD_BOTTOM . |
V4L2_FIELD_TOP |
2 | Images consist of the top field only. |
V4L2_FIELD_BOTTOM |
3 | Images consist of the bottom field only.Applications may wish to prevent a device from capturing interlacedimages because they will have "comb" or "feathering" artefacts aroundmoving objects. |
V4L2_FIELD_INTERLACED |
4 | Images contain both fields, interleaved line byline. The temporal order of the fields (whether the top or bottomfield is first transmitted) depends on the current video standard.M/NTSC transmits the bottom field first, all other standards the topfield first. |
V4L2_FIELD_SEQ_TB |
5 | Images contain both fields, the top field linesare stored first in memory, immediately followed by the bottom fieldlines. Fields are always stored in temporal order, the older one firstin memory. Image sizes refer to the frame, not fields. |
V4L2_FIELD_SEQ_BT |
6 | Images contain both fields, the bottom fieldlines are stored first in memory, immediately followed by the topfield lines. Fields are always stored in temporal order, the older onefirst in memory. Image sizes refer to the frame, not fields. |
V4L2_FIELD_ALTERNATE |
7 | The two fields of a frame are passed in separatebuffers, in temporal order, i. e. the older one first. To indicate the fieldparity (whether the current field is a top or bottom field) the driveror application, depending on data direction, must set struct v4l2_bufferfield toV4L2_FIELD_TOP orV4L2_FIELD_BOTTOM . Any two successive fields pairto build a frame. If fields are successive, without any dropped fieldsbetween them (fields can drop individually), can be determined fromthe struct v4l2_buffersequence field. Imagesizes refer to the frame, not fields. This format cannot be selectedwhen using the read/write I/O method. |
V4L2_FIELD_INTERLACED_TB |
8 | Images contain both fields, interleaved line byline, top field first. The top field is transmitted first. |
V4L2_FIELD_INTERLACED_BT |
9 | Images contain both fields, interleaved line byline, top field first. The bottom field is transmitted first. |
Chapter 4. Interfaces
4.1. Video Capture Interface
Video capture devices sample an analog video signal and storethe digitized images in memory. Today nearly all devices can captureat full 25 or 30 frames/second. With this interface applications cancontrol the capture process and move images from the driver into userspace.
Conventionally V4L2 video capture devices are accessed throughcharacter device special files named/dev/videoand/dev/video0 to/dev/video63 with major number 81 and minornumbers 0 to 63./dev/video is typically asymbolic link to the preferred video device. Note the same devicefiles are used for video output devices.
4.1.1. Querying Capabilities
Devices supporting the video capture interface set theV4L2_CAP_VIDEO_CAPTURE
flag in thecapabilities
field of struct v4l2_capabilityreturned by the VIDIOC_QUERYCAP
ioctl. As secondary device functionsthey may also support thevideo overlay(V4L2_CAP_VIDEO_OVERLAY
) and theraw VBI capture(V4L2_CAP_VBI_CAPTURE
) interface. At least one ofthe read/write or streaming I/O methods must be supported. Tuners andaudio inputs are optional.
4.1.2. Supplemental Functions
Video capture devices shall support audio input, tuner, controls,cropping and scaling andstreaming parameter ioctls as needed.Thevideo input andvideo standard ioctls must be supported byall video capture devices.
4.1.3. Image Format Negotiation
The result of a capture operation is determined bycropping and image format parameters. The former select an area of thevideo picture to capture, the latter how images are stored in memory,i. e. in RGB or YUV format, the number of bits per pixel or width andheight. Together they also define how images are scaled in theprocess.
As usual these parameters are not resetatopen()
time to permit Unix tool chains, programming a deviceand then reading from it as if it was a plain file. Well written V4L2applications ensure they really get what they want, including croppingand scaling.
Cropping initialization at minimum requires to reset theparameters to defaults. An example is given inSection 1.11.
To query the current image format applications set thetype
field of a struct v4l2_format toV4L2_BUF_TYPE_VIDEO_CAPTURE
and call theVIDIOC_G_FMT
ioctl with a pointer to this structure. Drivers fillthe struct v4l2_pix_formatpix
member of thefmt
union.
To request different parameters applications set thetype
field of a struct v4l2_format as above andinitialize all fields of the struct v4l2_pix_formatvbi
member of thefmt
union, or better just modify theresults ofVIDIOC_G_FMT
, and call theVIDIOC_S_FMT
ioctl with a pointer to this structure. Drivers mayadjust the parameters and finally return the actual parameters asVIDIOC_G_FMT
does.
Like VIDIOC_S_FMT
theVIDIOC_TRY_FMT
ioctl can be used to learn about hardware limitationswithout disabling I/O or possibly time consuming hardwarepreparations.
The contents of struct v4l2_pix_format are discussed inChapter 2. See also the specification of theVIDIOC_G_FMT
,VIDIOC_S_FMT
andVIDIOC_TRY_FMT
ioctls for details. Videocapture devices must implement both theVIDIOC_G_FMT
andVIDIOC_S_FMT
ioctl, even ifVIDIOC_S_FMT
ignores all requests and alwaysreturns default parameters asVIDIOC_G_FMT
does.VIDIOC_TRY_FMT
is optional.
4.1.4. Reading Images
A video capture device may support the read() function and/or streaming (memory mapping oruser pointer) I/O. SeeChapter 3 for details.
4.2. Video Overlay Interface
Also known as Framebuffer Overlay or PreviewingVideo overlay devices have the ability to genlock (TV-)videointo the (VGA-)video signal of a graphics card, or to store capturedimages directly in video memory of a graphics card, typically withclipping. This can be considerable more efficient than capturingimages and displaying them by other means. In the old days when onlynuclear power plants needed cooling towers this used to be the onlyway to put live video into a window.
Video overlay devices are accessed through the same characterspecial files as video capture devices.Note the default function of a /dev/video deviceis video capturing. The overlay function is only available aftercalling theVIDIOC_S_FMT
ioctl.
The driver may support simultaneous overlay and capturingusing the read/write and streaming I/O methods. If so, operation atthe nominal frame rate of the video standard is not guaranteed. Framesmay be directed away from overlay to capture, or one field may be usedfor overlay and the other for capture if the capture parameters permitthis.
Applications should use different file descriptors forcapturing and overlay. This must be supported by all drivers capableof simultaneous capturing and overlay. Optionally these drivers mayalso permit capturing and overlay with a single file descriptor forcompatibility with V4L and earlier versions of V4L2.[20]
4.2.1. Querying Capabilities
Devices supporting the video overlay interface set theV4L2_CAP_VIDEO_OVERLAY
flag in thecapabilities
field of struct v4l2_capabilityreturned by the VIDIOC_QUERYCAP
ioctl. The overlay I/O method specifiedbelow must be supported. Tuners and audio inputs are optional.
4.2.2. Supplemental Functions
Video overlay devices shall support audio input, tuner, controls,cropping and scaling andstreaming parameter ioctls as needed.Thevideo input andvideo standard ioctls must be supported byall video overlay devices.
4.2.3. Setup
Before overlay can commence applications must program thedriver with frame buffer parameters, namely the address and size ofthe frame buffer and the image format, for example RGB 5:6:5. TheVIDIOC_G_FBUF
and VIDIOC_S_FBUF
ioctls are available to getand set these parameters, respectively. TheVIDIOC_S_FBUF
ioctl is privileged because itallows to set up DMA into physical memory, bypassing the memoryprotection mechanisms of the kernel. Only the superuser can change theframe buffer address and size. Users are not supposed to run TVapplications as root or with SUID bit set. A small helper applicationwith suitable privileges should query the graphics system and programthe V4L2 driver at the appropriate time.
Some devices add the video overlay to the output signalof the graphics card. In this case the frame buffer is not modified bythe video device, and the frame buffer address and pixel format arenot needed by the driver. TheVIDIOC_S_FBUF
ioctlis not privileged. An application can check for this type of device bycalling theVIDIOC_G_FBUF
ioctl.
A driver may support any (or none) of five clipping/blendingmethods:
-
Chroma-keying displays the overlaid image only wherepixels in the primary graphics surface assume a certain color.
-
A bitmap can be specified where each bit correspondsto a pixel in the overlaid image. When the bit is set, thecorresponding video pixel is displayed, otherwise a pixel of thegraphics surface.
-
A list of clipping rectangles can be specified. Inthese regions no video is displayed, so thegraphics surface can be seen here.
-
The framebuffer has an alpha channel that can be usedto clip or blend the framebuffer with the video.
-
A global alpha value can be specified to blend theframebuffer contents with video images.
When simultaneous capturing and overlay is supported andthe hardware prohibits different image and frame buffer formats, theformat requested first takes precedence. The attempt to capture(VIDIOC_S_FMT
) or overlay (VIDIOC_S_FBUF
) may fail with anEBUSY error code or return accordingly modified parameters..
4.2.4. Overlay Window
The overlaid image is determined by cropping and overlaywindow parameters. The former select an area of the video picture tocapture, the latter how images are overlaid and clipped. Croppinginitialization at minimum requires to reset the parameters todefaults. An example is given in Section 1.11.
The overlay window is described by a struct v4l2_window. Itdefines the size of the image, its position over the graphics surfaceand the clipping to be applied. To get the current parametersapplications set the type
field of astruct v4l2_format toV4L2_BUF_TYPE_VIDEO_OVERLAY
andcall theVIDIOC_G_FMT
ioctl. The driver fills thev4l2_window
substructure namedwin
. It is not possible to retrieve apreviously programmed clipping list or bitmap.
To program the overlay window applications set thetype
field of a struct v4l2_format toV4L2_BUF_TYPE_VIDEO_OVERLAY
, initialize thewin
substructure and call theVIDIOC_S_FMT
ioctl. The driver adjusts the parameters againsthardware limits and returns the actual parameters asVIDIOC_G_FMT
does. LikeVIDIOC_S_FMT
, theVIDIOC_TRY_FMT
ioctl can beused to learn about driver capabilities without actually changingdriver state. UnlikeVIDIOC_S_FMT
this also worksafter the overlay has been enabled.
The scaling factor of the overlaid image is implied by thewidth and height given in struct v4l2_window and the size of the croppingrectangle. For more information seeSection 1.11.
When simultaneous capturing and overlay is supported andthe hardware prohibits different image and window sizes, the sizerequested first takes precedence. The attempt to capture or overlay aswell (VIDIOC_S_FMT
) may fail with an EBUSY error code or return accordinglymodified parameters.
Table 4-1. struct v4l2_window
struct v4l2_rect | w |
Size and position of the window relative to thetop, left corner of the frame buffer defined withVIDIOC_S_FBUF . Thewindow can extend the frame buffer width and height, thex andy coordinates can be negative, and it can lie completely outside theframe buffer. The driver clips the window accordingly, or if that isnot possible, modifies its size and/or position. |
enum v4l2_field | field |
Applications set this field to determine whichvideo field shall be overlaid, typically one ofV4L2_FIELD_ANY (0),V4L2_FIELD_TOP ,V4L2_FIELD_BOTTOM orV4L2_FIELD_INTERLACED . Drivers may have to choosea different field order and return the actual setting here. |
__u32 | chromakey |
When chroma-keying has been negotiated withVIDIOC_S_FBUF applications set this field to the desired pixel valuefor the chroma key. The format is the same as the pixel format of theframebuffer (struct v4l2_framebufferfmt.pixelformat field), with bytes in hostorder. E. g. forV4L2_PIX_FMT_BGR24 the value should be 0xRRGGBB on a little endian, 0xBBGGRR on a bigendian host. |
struct v4l2_clip * | clips |
When chroma-keying has notbeen negotiated andVIDIOC_G_FBUF indicated this capability,applications can set this field to point to an array ofclipping rectangles. |
Like the window coordinatesw , clipping rectangles are defined relativeto the top, left corner of the frame buffer. However clippingrectangles must not extend the frame buffer width and height, and theymust not overlap. If possible applications should merge adjacentrectangles. Whether this must create x-y or y-x bands, or the order ofrectangles, is not defined. When clip lists are not supported thedriver ignores this field. Its contents after callingVIDIOC_S_FMT are undefined. |
||
__u32 | clipcount |
When the application set theclips field, this field must contain thenumber of clipping rectangles in the list. When clip lists are notsupported the driver ignores this field, its contents after callingVIDIOC_S_FMT are undefined. When clip lists aresupported but no clipping is desired this field must be set tozero. |
void * | bitmap |
When chroma-keying hasnot been negotiated andVIDIOC_G_FBUF indicatedthis capability, applications can set this field to point to aclipping bit mask. |
It must be of the same sizeas the window, ((__u8 *) where When a clippingbit mask is not supported the driver ignores this field, its contentsafter calling Applications need not create aclip list or bit mask. When they pass both, or despite negotiatingchroma-keying, the results are undefined. Regardless of the chosenmethod, the clipping abilities of the hardware may be limited inquantity or quality. The results when these limits are exceeded areundefined.b |
||
__u8 | global_alpha |
The global alpha value used to blend theframebuffer with video images, if global alpha blending has beennegotiated ( Notethis field was added in Linux 2.6.23, extending the structure. Howeverthe VIDIOC_G/S/TRY_FMT ioctls,which take a pointer to a v4l2_format parent structure with paddingbytes at the end, are not affected. |
Notes: a. Should we require w.width to be a multiple of eight?b. When the image is written into frame buffermemory it will be undesirable if the driver clips out less pixelsthan expected, because the application and graphics system are notaware these regions need to be refreshed. The driver should clip outmore pixels or not write the image at all. |
Table 4-2. struct v4l2_clip
[21]
struct v4l2_rect | c |
Coordinates of the clipping rectangle, relative tothe top, left corner of the frame buffer. Only window pixelsoutside all clipping rectangles aredisplayed. |
struct v4l2_clip * | next |
Pointer to the next clipping rectangle, NULL whenthis is the last rectangle. Drivers ignore this field, it cannot beused to pass a linked list of clipping rectangles. |
Table 4-3. struct v4l2_rect
__s32 | left |
Horizontal offset of the top, left corner of therectangle, in pixels. |
__s32 | top |
Vertical offset of the top, left corner of therectangle, in pixels. Offsets increase to the right and down. |
__s32 | width |
Width of the rectangle, in pixels. |
__s32 | height |
Height of the rectangle, in pixels. Width andheight cannot be negative, the fields are signed for hystericalreasons. |
4.2.5. Enabling Overlay
To start or stop the frame buffer overlay applications callthe VIDIOC_OVERLAY
ioctl.
4.3. Video Output Interface
Video output devices encode stills or image sequences asanalog video signal. With this interface applications cancontrol the encoding process and move images from user space tothe driver.
Conventionally V4L2 video output devices are accessed throughcharacter device special files named/dev/videoand/dev/video0 to/dev/video63 with major number 81 and minornumbers 0 to 63./dev/video is typically asymbolic link to the preferred video device. Note the same devicefiles are used for video capture devices.
4.3.1. Querying Capabilities
Devices supporting the video output interface set theV4L2_CAP_VIDEO_OUTPUT
flag in thecapabilities
field of struct v4l2_capabilityreturned by the VIDIOC_QUERYCAP
ioctl. As secondary device functionsthey may also support theraw VBIoutput (V4L2_CAP_VBI_OUTPUT
) interface. Atleast one of the read/write or streaming I/O methods must besupported. Modulators and audio outputs are optional.
4.3.2. Supplemental Functions
Video output devices shall support audio output, modulator, controls,cropping and scaling andstreaming parameter ioctls as needed.Thevideo output andvideo standard ioctls must be supported byall video output devices.
4.3.3. Image Format Negotiation
The output is determined by cropping and image formatparameters. The former select an area of the video picture where theimage will appear, the latter how images are stored in memory, i. e. inRGB or YUV format, the number of bits per pixel or width and height.Together they also define how images are scaled in the process.
As usual these parameters are not resetatopen()
time to permit Unix tool chains, programming a deviceand then writing to it as if it was a plain file. Well written V4L2applications ensure they really get what they want, including croppingand scaling.
Cropping initialization at minimum requires to reset theparameters to defaults. An example is given inSection 1.11.
To query the current image format applications set thetype
field of a struct v4l2_format toV4L2_BUF_TYPE_VIDEO_OUTPUT
and call theVIDIOC_G_FMT
ioctl with a pointer to this structure. Drivers fillthe struct v4l2_pix_formatpix
member of thefmt
union.
To request different parameters applications set thetype
field of a struct v4l2_format as above andinitialize all fields of the struct v4l2_pix_formatvbi
member of thefmt
union, or better just modify theresults ofVIDIOC_G_FMT
, and call theVIDIOC_S_FMT
ioctl with a pointer to this structure. Drivers mayadjust the parameters and finally return the actual parameters asVIDIOC_G_FMT
does.
Like VIDIOC_S_FMT
theVIDIOC_TRY_FMT
ioctl can be used to learn about hardware limitationswithout disabling I/O or possibly time consuming hardwarepreparations.
The contents of struct v4l2_pix_format are discussed inChapter 2. See also the specification of theVIDIOC_G_FMT
,VIDIOC_S_FMT
andVIDIOC_TRY_FMT
ioctls for details. Videooutput devices must implement both theVIDIOC_G_FMT
andVIDIOC_S_FMT
ioctl, even ifVIDIOC_S_FMT
ignores all requests and alwaysreturns default parameters asVIDIOC_G_FMT
does.VIDIOC_TRY_FMT
is optional.
4.3.4. Writing Images
A video output device may support the write() function and/or streaming (memory mapping oruser pointer) I/O. SeeChapter 3 for details.
4.4. Video Output Overlay Interface
Also known as On-Screen Display (OSD)Experimental: This is an experimentalinterface and may change in the future.
Some video output devices can overlay a framebuffer image ontothe outgoing video signal. Applications can set up such an overlayusing this interface, which borrows structures and ioctls of theVideo Overlay interface.
The OSD function is accessible through the same characterspecial file as the Video Output function.Note the default function of such a /dev/video deviceis video capturing or output. The OSD function is only available aftercalling theVIDIOC_S_FMT
ioctl.
4.4.1. Querying Capabilities
Devices supporting the Video OutputOverlay interface set theV4L2_CAP_VIDEO_OUTPUT_OVERLAY
flag in thecapabilities
field of struct v4l2_capabilityreturned by the VIDIOC_QUERYCAP
ioctl.
4.4.2. Framebuffer
Contrary to the Video Overlayinterface the framebuffer is normally implemented on the TV card andnot the graphics card. On Linux it is accessible as a framebufferdevice (/dev/fbN). Given a V4L2 device,applications can find the corresponding framebuffer device by callingthe VIDIOC_G_FBUF
ioctl. It returns, amongst other information, thephysical address of the framebuffer in thebase
field of struct v4l2_framebuffer. Theframebuffer device ioctl FBIOGET_FSCREENINFO
returns the same address in thesmem_start
field of structfb_fix_screeninfo
. TheFBIOGET_FSCREENINFO
ioctl and structfb_fix_screeninfo
are defined in thelinux/fb.h header file.
The width and height of the framebuffer depends on thecurrent video standard. A V4L2 driver may reject attempts to changethe video standard (or any other ioctl which would imply a framebuffersize change) with anEBUSY error code until all applications closed theframebuffer device.
Example 4-1. Finding a framebuffer device for OSD
#include <linux/fb.h> struct v4l2_framebuffer fbuf; unsigned int i; int fb_fd; if (-1 == ioctl (fd, VIDIOC_G_FBUF, &fbuf)) { perror ("VIDIOC_G_FBUF"); exit (EXIT_FAILURE); } for (i = 0; i < 30; ++i) { char dev_name[16]; struct fb_fix_screeninfo si; snprintf (dev_name, sizeof (dev_name), "/dev/fb%u", i); fb_fd = open (dev_name, O_RDWR); if (-1 == fb_fd) { switch (errno) { case ENOENT: /* no such file */ case ENXIO: /* no driver */ continue; default: perror ("open"); exit (EXIT_FAILURE); } } if (0 == ioctl (fb_fd, FBIOGET_FSCREENINFO, &si)) { if (si.smem_start == (unsigned long) fbuf.base) break; } else { /* Apparently not a framebuffer device. */ } close (fb_fd); fb_fd = -1; } /* fb_fd is the file descriptor of the framebuffer device for the video output overlay, or -1 if no device was found. */
4.4.3. Overlay Window and Scaling
The overlay is controlled by source and target rectangles.The source rectangle selects a subsection of the framebuffer image tobe overlaid, the target rectangle an area in the outgoing video signalwhere the image will appear. Drivers may or may not support scaling,and arbitrary sizes and positions of these rectangles. Further driversmay support any (or none) of the clipping/blending methods defined fortheVideo Overlay interface.
A struct v4l2_window defines the size of the source rectangle,its position in the framebuffer and the clipping/blending method to beused for the overlay. To get the current parameters applications setthe type
field of a struct v4l2_format toV4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY
and call theVIDIOC_G_FMT
ioctl. The driver fills thev4l2_window
substructure namedwin
. It is not possible to retrieve apreviously programmed clipping list or bitmap.
To program the source rectangle applications set thetype
field of a struct v4l2_format toV4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY
, initializethe win
substructure and call theVIDIOC_S_FMT
ioctl. The driver adjusts the parameters againsthardware limits and returns the actual parameters asVIDIOC_G_FMT
does. LikeVIDIOC_S_FMT
, theVIDIOC_TRY_FMT
ioctl can beused to learn about driver capabilities without actually changingdriver state. UnlikeVIDIOC_S_FMT
this also worksafter the overlay has been enabled.
A struct v4l2_crop defines the size and position of the targetrectangle. The scaling factor of the overlay is implied by the widthand height given in struct v4l2_window and struct v4l2_crop. The cropping APIapplies toVideo Output andVideoOutput Overlay devices in the same way as toVideo Capture andVideoOverlay devices, merely reversing the direction of thedata flow. For more information seeSection 1.11.
4.5. Codec Interface
Suspended: This interface has been be suspended from the V4L2 APIimplemented in Linux 2.6 until we have more experience with codecdevice interfaces.
A V4L2 codec can compress, decompress, transform, or otherwiseconvert video data from one format into another format, in memory.Applications send data to be converted to the driver through awrite()
call, and receive the converted data through aread()
call. For efficiency a driver may also support streamingI/O.
[to do]
4.6. Effect Devices Interface
Suspended: This interface has been be suspended from the V4L2 APIimplemented in Linux 2.6 until we have more experience with effectdevice interfaces.
A V4L2 video effect device can do image effects, filtering, orcombine two or more images or image streams. For example videotransitions or wipes. Applications send data to be processed andreceive the result data either withread()
andwrite()
functions, or through the streaming I/O mechanism.
[to do]
4.7. Raw VBI Data Interface
VBI is an abbreviation of Vertical Blanking Interval, a gapin the sequence of lines of an analog video signal. During VBIno picture information is transmitted, allowing some time while theelectron beam of a cathode ray tube TV returns to the top of thescreen. Using an oscilloscope you will find here the verticalsynchronization pulses and short data packages ASKmodulated[22]onto the video signal. These are transmissions of services such asTeletext or Closed Caption.
Subject of this interface type is raw VBI data, as sampled offa video signal, or to be added to a signal for output.The data format is similar to uncompressed video images, a number oflines times a number of samples per line, we call this a VBI image.
Conventionally V4L2 VBI devices are accessed through characterdevice special files named/dev/vbi and/dev/vbi0 to/dev/vbi31 withmajor number 81 and minor numbers 224 to 255./dev/vbi is typically a symbolic link to thepreferred VBI device. This convention applies to both input and outputdevices.
To address the problems of finding related video and VBIdevices VBI capturing and output is also available as device functionunder/dev/video. To capture or output raw VBIdata with these devices applications must call theVIDIOC_S_FMT
ioctl. Accessed as/dev/vbi, raw VBI capturingor output is the default device function.
4.7.1. Querying Capabilities
Devices supporting the raw VBI capturing or output API setthe V4L2_CAP_VBI_CAPTURE
orV4L2_CAP_VBI_OUTPUT
flags, respectively, in thecapabilities
field of struct v4l2_capabilityreturned by the VIDIOC_QUERYCAP
ioctl. At least one of theread/write, streaming or asynchronous I/O methods must besupported. VBI devices may or may not have a tuner or modulator.
4.7.2. Supplemental Functions
VBI devices shall support videoinput or output, tuner ormodulator, and controls ioctlsas needed. The video standard ioctls provideinformation vital to program a VBI device, therefore must besupported.
4.7.3. Raw VBI Format Negotiation
Raw VBI sampling abilities can vary, in particular thesampling frequency. To properly interpret the data V4L2 specifies anioctl to query the sampling parameters. Moreover, to allow for someflexibility applications can also suggest different parameters.
As usual these parameters are notreset atopen()
time to permit Unix tool chains, programming adevice and then reading from it as if it was a plain file. Wellwritten V4L2 applications should always ensure they really get whatthey want, requesting reasonable parameters and then checking if theactual parameters are suitable.
To query the current raw VBI capture parametersapplications set the type
field of astruct v4l2_format toV4L2_BUF_TYPE_VBI_CAPTURE
orV4L2_BUF_TYPE_VBI_OUTPUT
, and call theVIDIOC_G_FMT
ioctl with a pointer to this structure. Drivers fillthe struct v4l2_vbi_formatvbi
member of thefmt
union.
To request different parameters applications set thetype
field of a struct v4l2_format as above andinitialize all fields of the struct v4l2_vbi_formatvbi
member of thefmt
union, or better just modify theresults ofVIDIOC_G_FMT
, and call theVIDIOC_S_FMT
ioctl with a pointer to this structure. Drivers returnanEINVAL error code only when the given parameters are ambiguous, otherwisethey modify the parameters according to the hardware capabilites andreturn the actual parameters. When the driver allocates resources atthis point, it may return an EBUSY error code to indicate the returnedparameters are valid but the required resources are currently notavailable. That may happen for instance when the video and VBI areasto capture would overlap, or when the driver supports multiple opensand another process already requested VBI capturing or output. Anyway,applications must expect other resource allocation points which mayreturnEBUSY, at theVIDIOC_STREAMON
ioctland the first read(), write() and select() call.
VBI devices must implement both theVIDIOC_G_FMT
andVIDIOC_S_FMT
ioctl, even ifVIDIOC_S_FMT
ignores all requests and alwaysreturns default parameters asVIDIOC_G_FMT
does.VIDIOC_TRY_FMT
is optional.
Table 4-4. struct v4l2_vbi_format
__u32 | sampling_rate |
Samples per second, i. e. unit 1 Hz. |
__u32 | offset |
Horizontal offset of the VBI image,relative to the leading edge of the line synchronization pulse andcounted in samples: The first sample in the VBI image will be located |
__u32 | samples_per_line |
|
__u32 | sample_format |
Defines the sample format as in Chapter 2, a four-character-code.a Usually this is |
__u32 | start [2] |
This is the scanning system line numberassociated with the first line of the VBI image, of the first and thesecond field respectively. SeeFigure 4-2 andFigure 4-3 for valid values. VBI input drivers canreturn start values 0 if the hardware cannot reliable identifyscanning lines, VBI acquisition may not require thisinformation. |
__u32 | count [2] |
The number of lines in the first and secondfield image, respectively. |
Drivers should be asflexibility as possible. For example, it may be possible to extend ormove the VBI capture window down to the picture area, implementing a'full field mode' to capture data service transmissions embedded inthe picture. An application can set the first or second Both To initialize the |
||
__u32 | flags |
See Table 4-5 below. Currentlyonly drivers set flags, applications must set this field tozero. |
__u32 | reserved [2] |
This array is reserved for future extensions.Drivers and applications must set it to zero. |
Notes: a. A few devices may be unable tosample VBI data at all but can extend the video capture window to theVBI region. |
Table 4-5. Raw VBI Format Flags
V4L2_VBI_UNSYNC |
0x0001 | This flag indicates hardware which does notproperly distinguish between fields. Normally the VBI image stores thefirst field (lower scanning line numbers) first in memory. This may bea top or bottom field depending on the video standard. When this flagis set the first or second field may be stored first, however thefields are still in correct temporal order with the older field firstin memory.a |
V4L2_VBI_INTERLACED |
0x0002 | By default the two field images will be passedsequentially; all lines of the first field followed by all lines ofthe second field (compareSection 3.6V4L2_FIELD_SEQ_TB andV4L2_FIELD_SEQ_BT , whether the top or bottomfield is first in memory depends on the video standard). When thisflag is set, the two fields are interlaced (cf.V4L2_FIELD_INTERLACED ). The first line of thefirst field followed by the first line of the second field, then thetwo second lines, and so on. Such a layout may be necessary when thehardware has been programmed to capture or output interlaced videoimages and is unable to separate the fields for VBI capturing atthe same time. For simplicity setting this flag implies that bothcount values are equal and non-zero. |
Notes: a. Most VBI services transmit on both fields, butsome have different semantics depending on the field number. Thesecannot be reliable decoded or encoded when V4L2_VBI_UNSYNC is set. |
Figure 4-2. ITU-R 525 line numbering (M/NTSC and M/PAL)
(1) For the purpose of this specification field 2starts in line 264 and not 263.5 because half line capturing is notsupported.
Figure 4-3. ITU-R 625 line numbering
(1) For the purpose of this specification field 2starts in line 314 and not 313.5 because half line capturing is notsupported.
Remember the VBI image format depends on the selectedvideo standard, therefore the application must choose a new standard orquery the current standard first. Attempts to read or write data aheadof format negotiation, or after switching the video standard which mayinvalidate the negotiated VBI parameters, should be refused by thedriver. A format change during active I/O is not permitted.
4.7.4. Reading and writing VBI images
To assure synchronization with the field number and easierimplementation, the smallest unit of data passed at a time is oneframe, consisting of two fields of VBI images immediately following inmemory.
The total size of a frame computes as follows:
(count
[0] +count
[1]) *samples_per_line
* sample size in bytes
The sample size is most likely always one byte,applications must check the sample_format
field though, to function properly with other drivers.
A VBI device may support read/write and/or streaming (memory mapping oruser pointer) I/O. The latter bears thepossibility of synchronizing video andVBI data by using buffer timestamps.
Remember the VIDIOC_STREAMON
ioctl and the first read(),write() and select() call can be resource allocation points returninganEBUSY error code if the required hardware resources are temporarilyunavailable, for example the device is already in use by anotherprocess.
4.8. Sliced VBI Data Interface
VBI stands for Vertical Blanking Interval, a gap in thesequence of lines of an analog video signal. During VBI no pictureinformation is transmitted, allowing some time while the electron beamof a cathode ray tube TV returns to the top of the screen.
Sliced VBI devices use hardware to demodulate data transmittedin the VBI. V4L2 drivers shallnot do this bysoftware, see also theraw VBIinterface. The data is passed as short packets of fixed size,covering one scan line each. The number of packets per video frame isvariable.
Sliced VBI capture and output devices are accessed through thesame character special files as raw VBI devices. When a driversupports both interfaces, the default function of a/dev/vbi device israw VBIcapturing or output, and the sliced VBI function is only availableafter calling theVIDIOC_S_FMT
ioctl as defined below. Likewise a/dev/video device may support the sliced VBI API,however the default function here is video capturing or output.Different file descriptors must be used to pass raw and sliced VBIdata simultaneously, if this is supported by the driver.
4.8.1. Querying Capabilities
Devices supporting the sliced VBI capturing or output APIset the V4L2_CAP_SLICED_VBI_CAPTURE
orV4L2_CAP_SLICED_VBI_OUTPUT
flag respectively, inthecapabilities
field of struct v4l2_capabilityreturned by theVIDIOC_QUERYCAP
ioctl. At least one of theread/write, streaming or asynchronousI/Omethods must be supported. Sliced VBI devices may have a tuneror modulator.
4.8.2. Supplemental Functions
Sliced VBI devices shall support videoinput or output and tuner ormodulator ioctls if they have these capabilities, and they maysupportcontrol ioctls. Thevideo standard ioctls provide informationvital to program a sliced VBI device, therefore must besupported.
4.8.3. Sliced VBI Format Negotiation
To find out which data services are supported by thehardware applications can call theVIDIOC_G_SLICED_VBI_CAP
ioctl.All drivers implementing the sliced VBI interface must support thisioctl. The results may differ from those of theVIDIOC_S_FMT
ioctlwhen the number of VBI lines the hardware can capture or output perframe, or the number of services it can identify on a given line arelimited. For example on PAL line 16 the hardware may be able to lookfor a VPS or Teletext signal, but not both at the same time.
To determine the currently selected services applicationsset the type
field of struct v4l2_format to V4L2_BUF_TYPE_SLICED_VBI_CAPTURE
orV4L2_BUF_TYPE_SLICED_VBI_OUTPUT
, and theVIDIOC_G_FMT
ioctl fills thefmt.sliced
member, astruct v4l2_sliced_vbi_format.
Applications can request different parameters byinitializing or modifying the fmt.sliced
member and calling the VIDIOC_S_FMT
ioctl with a pointer to thev4l2_format
structure.
The sliced VBI API is more complicated than the raw VBI APIbecause the hardware must be told which VBI service to expect on eachscan line. Not all services may be supported by the hardware on alllines (this is especially true for VBI output where Teletext is oftenunsupported and other services can only be inserted in one specificline). In many cases, however, it is sufficient to just set theservice_set
field to the required servicesand let the driver fill theservice_lines
array according to hardware capabilities. Only if more precise controlis needed should the programmer set theservice_lines
array explicitly.
The VIDIOC_S_FMT
ioctl returns anEINVAL error code only when thegiven parameters are ambiguous, otherwise it modifies the parametersaccording to hardware capabilities. When the driver allocatesresources at this point, it may return anEBUSY error code if the requiredresources are temporarily unavailable. Other resource allocationpoints which may returnEBUSY can be theVIDIOC_STREAMON
ioctl and the firstread()
,write()
andselect()
call.
Table 4-6. structv4l2_sliced_vbi_format
__u32 | service_set |
If On return the driver sets this field to the union of allelements of the returned |
||
__u16 | service_lines [2][24] |
Applications initialize thisarray with sets of data services the driver shall look for or inserton the respective scan line. Subject to hardware capabilities driversreturn the requested set, a subset, which may be just a singleservice, or an empty set. When the hardware cannot handle multipleservices on the same line the driver shall choose one. No assumptionscan be made on which service the driver chooses. Dataservices are defined in Table 4-7. Array indicesmap to ITU-R line numbers (see also Figure 4-2 and Figure 4-3) as follows: |
||
Element | 525 line systems | 625 line systems | ||
service_lines [0][1] |
1 | 1 | ||
service_lines [0][23] |
23 | 23 | ||
service_lines [1][1] |
264 | 314 | ||
service_lines [1][23] |
286 | 336 | ||
Drivers must setservice_lines [0][0] andservice_lines [1][0] to zero. |
||||
__u32 | io_size |
Maximum number of bytes passed byone read() or write() call, and the buffer size in bytes fortheVIDIOC_QBUF andVIDIOC_DQBUF ioctl. Drivers set this field tothe size of struct v4l2_sliced_vbi_data times the number of non-zeroelements in the returnedservice_lines array (that is the number of lines potentially carrying data). |
||
__u32 | reserved [2] |
This array is reserved for futureextensions. Applications and drivers must set it to zero. | ||
Notes: a. According to ETS 300 706 lines 6-22 of thefirst field and lines 5-22 of the second field may carry Teletextdata. |
Table 4-7. Sliced VBI services
Symbol | Value | Reference | Lines, usually | Payload |
---|---|---|---|---|
V4L2_SLICED_TELETEXT_B (Teletext System B) |
0x0001 | ETS 300 706,ITU BT.653 | PAL/SECAM line 7-22, 320-335 (second field 7-22) | Last 42 of the 45 byte Teletext packet, that iswithout clock run-in and framing code, lsb first transmitted. |
V4L2_SLICED_VPS |
0x0400 | ETS 300 231 | PAL line 16 | Byte number 3 to 15 according to Figure 9 ofETS 300 231, lsb first transmitted. |
V4L2_SLICED_CAPTION_525 |
0x1000 | EIA 608-B | NTSC line 21, 284 (second field 21) | Two bytes in transmission order, including paritybit, lsb first transmitted. |
V4L2_SLICED_WSS_625 |
0x4000 | ITU BT.1119,EN 300 294 | PAL/SECAM line 23 | Byte 0 1 msb lsb msb lsb Bit 7 6 5 4 3 2 1 0 x x 13 12 11 10 9 |
V4L2_SLICED_VBI_525 |
0x1000 | Set of services applicable to 525line systems. | ||
V4L2_SLICED_VBI_625 |
0x4401 | Set of services applicable to 625line systems. |
Drivers may return an EINVAL error code when applications attempt toread or write data without prior format negotiation, after switchingthe video standard (which may invalidate the negotiated VBIparameters) and after switching the video input (which may change thevideo standard as a side effect). The VIDIOC_S_FMT
ioctl may returnan EBUSY error code when applications attempt to change the format while i/o isin progress (between aVIDIOC_STREAMON
andVIDIOC_STREAMOFF
call,and after the firstread()
orwrite()
call).
4.8.4. Reading and writing sliced VBI data
A single read()
or write()
call must pass all databelonging to one video frame. That is an array ofv4l2_sliced_vbi_data
structures with one ormore elements and a total size not exceedingio_size
bytes. Likewise in streaming I/Omode one buffer of io_size
bytes mustcontain data of one video frame. Theid
ofunusedv4l2_sliced_vbi_data
elements must bezero.
Table 4-8. structv4l2_sliced_vbi_data
__u32 | id |
A flag from Table 2identifying the type of data in this packet. Only a single bit must beset. When theid of a captured packet iszero, the packet is empty and the contents of other fields areundefined. Applications shall ignore empty packets. When theid of a packet for output is zero thecontents of thedata field are undefinedand the driver must no longer insert data on the requestedfield andline . |
__u32 | field |
The video field number this data has been capturedfrom, or shall be inserted at.0 for the firstfield,1 for the second field. |
__u32 | line |
The field (as opposed to frame) line number thisdata has been captured from, or shall be inserted at. SeeFigure 4-2 andFigure 4-3 for validvalues. Sliced VBI capture devices can set the line number of allpackets to0 if the hardware cannot reliablyidentify scan lines. The field number must always be valid. |
__u32 | reserved |
This field is reserved for future extensions.Applications and drivers must set it to zero. |
__u8 | data [48] |
The packet payload. See Table 2 for the contents and number ofbytes passed for each data type. The contents of padding bytes at theend of this array are undefined, drivers and applications shall ignorethem. |
Packets are always passed in ascending line number order,without duplicate line numbers. Thewrite()
function and theVIDIOC_QBUF
ioctl must return an EINVAL error code when applications violatethis rule. They must also return anEINVAL error code when applications pass anincorrect field or line number, or a combination offield
,line
andid
which has not been negotiated with theVIDIOC_G_FMT
orVIDIOC_S_FMT
ioctl. When the line numbers areunknown the driver must pass the packets in transmitted order. Thedriver can insert empty packets withid
setto zero anywhere in the packet array.
To assure synchronization and to distinguish from framedropping, when a captured frame does not carry any of the requesteddata services drivers must pass one or more empty packets. When anapplication fails to pass VBI data in time for output, the drivermust output the last VPS and WSS packet again, and disable the outputof Closed Caption and Teletext data, or output data which is ignoredby Closed Caption and Teletext decoders.
A sliced VBI device may support read/write and/or streaming (memory mapping and/oruserpointer) I/O. The latter bears the possibility of synchronizingvideo and VBI data by using buffer timestamps.
4.9. Teletext Interface
This interface aims at devices receiving and demodulatingTeletext data [ETS 300 706,ITU BT.653], evaluating theTeletext packages and storing formatted pages in cache memory. Suchdevices are usually implemented as microcontrollers with serialinterface (I2C) and can be found on olderTV cards, dedicated Teletext decoding cards and home-brew devicesconnected to the PC parallel port.
The Teletext API was designed by Martin Buck. It is defined inthe kernel header filelinux/videotext.h, thespecification is available fromhttp://home.pages.de/~videotext/. (Videotext is the name ofthe German public television Teletext service.) Conventional characterdevice file names are/dev/vtx and/dev/vttuner, with device number 83, 0 and 83, 16respectively. A similar interface exists for the Philips SAA5249Teletext decoder [specification?] with character device file names/dev/tlkN, device number 102, N.
Eventually the Teletext API was integrated into the V4L APIwith character device file names/dev/vtx0 to/dev/vtx31, device major number 81, minor numbers192 to 223. For reference the V4L Teletext API specification isreproduced here in full: "Teletext interfaces talk the existing VTXAPI." Teletext devices with major number 83 and 102 will be removed inLinux 2.6.
There are no plans to replace the Teletext API or to integrateit into V4L2. Please write to the Video4Linux mailing list:https://listman.redhat.com/mailman/listinfo/video4linux-list when the need arises.
4.10. Radio Interface
This interface is intended for AM and FM (analog) radioreceivers.
Conventionally V4L2 radio devices are accessed throughcharacter device special files named/dev/radioand/dev/radio0 to/dev/radio63 with major number 81 and minornumbers 64 to 127.
4.10.1. Querying Capabilities
Devices supporting the radio interface set theV4L2_CAP_RADIO
andV4L2_CAP_TUNER
flag in thecapabilities
field of struct v4l2_capabilityreturned by the VIDIOC_QUERYCAP
ioctl. Other combinations ofcapability flags are reserved for future extensions.
4.10.2. Supplemental Functions
Radio devices can support controls, and must support the tuner ioctls.
They do not support the video input or output, audio inputor output, video standard, cropping and scaling, compression andstreaming parameter, or overlay ioctls. All other ioctls and I/Omethods are reserved for future extensions.
4.10.3. Programming
Radio devices may have a couple audio controls (as discussedin Section 1.8) such as a volume control, possibly customcontrols. Further all radio devices have one tuner (these arediscussed inSection 1.6) with index number zero to selectthe radio frequency and to determine if a monaural or FM stereoprogram is received. Drivers switch automatically between AM and FMdepending on the selected frequency. TheVIDIOC_G_TUNER
ioctlreports the supported frequency range.
4.11. RDS Interface
The Radio Data System transmits supplementaryinformation in binary format, for example the station name or travelinformation, on a inaudible audio subcarrier of a radio program. Thisinterface aims at devices capable of receiving and decoding RDSinformation.
The V4L API defines its RDS API as follows.
From radio devices supporting it, RDS data can be readwith the read()
function. The data is packed in groups of three,as follows:
-
First Octet Least Significant Byte of RDS Block
-
Second Octet Most Significant Byte of RDS Block
-
Third Octet Bit 7: Error bit. Indicates that anuncorrectable error occurred during reception of this block. Bit 6:Corrected bit. Indicates that an error was corrected for this datablock. Bits 5-3: Received Offset. Indicates the offset received by thesync system. Bits 2-0: Offset Name. Indicates the offset applied tothis data.
It was argued the RDS API should beextended before integration into V4L2, no new API has been devised yet.Please write to the Video4Linux mailing list for discussion:https://listman.redhat.com/mailman/listinfo/video4linux-list. Meanwhile no V4L2 driver should set theV4L2_CAP_RDS_CAPTURE
capability flag.
I. Function Reference
- Table of Contents
- V4L2 close() -- Close a V4L2 device
- V4L2 ioctl() -- Program a V4L2 device
- ioctl VIDIOC_CROPCAP -- Information about the video cropping and scaling abilities
- ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER -- Read or write hardware registers
- ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD -- Execute an encoder command
- ioctl VIDIOC_ENUMAUDIO -- Enumerate audio inputs
- ioctl VIDIOC_ENUMAUDOUT -- Enumerate audio outputs
- ioctl VIDIOC_ENUM_FMT -- Enumerate image formats
- ioctl VIDIOC_ENUM_FRAMESIZES -- Enumerate frame sizes
- ioctl VIDIOC_ENUM_FRAMEINTERVALS -- Enumerate frame intervals
- ioctl VIDIOC_ENUMINPUT -- Enumerate video inputs
- ioctl VIDIOC_ENUMOUTPUT -- Enumerate video outputs
- ioctl VIDIOC_ENUMSTD -- Enumerate supported video standards
- ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO -- Query or select the current audio input and itsattributes
- ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT -- Query or select the current audio output
- ioctl VIDIOC_G_CHIP_IDENT -- Identify the chips on a TV card
- ioctl VIDIOC_G_CROP, VIDIOC_S_CROP -- Get or set the current cropping rectangle
- ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL -- Get or set the value of a control
- ioctl VIDIOC_G_ENC_INDEX -- Get meta data about a compressed video stream
- ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,VIDIOC_TRY_EXT_CTRLS -- Get or set the value of several controls, try controlvalues
- ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF -- Get or set frame buffer overlay parameters
- ioctl VIDIOC_G_FMT, VIDIOC_S_FMT,VIDIOC_TRY_FMT -- Get or set the data format, try a format
- ioctl VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY -- Get or set tuner or modulator radiofrequency
- ioctl VIDIOC_G_INPUT, VIDIOC_S_INPUT -- Query or select the current video input
- ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP --
- ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR -- Get or set modulator attributes
- ioctl VIDIOC_G_OUTPUT, VIDIOC_S_OUTPUT -- Query or select the current video output
- ioctl VIDIOC_G_PARM, VIDIOC_S_PARM -- Get or set streaming parameters
- ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY -- Query or request the access priority associated with afile descriptor
- ioctl VIDIOC_G_SLICED_VBI_CAP -- Query sliced VBI capabilities
- ioctl VIDIOC_G_STD, VIDIOC_S_STD -- Query or select the video standard of the current input
- ioctl VIDIOC_G_TUNER, VIDIOC_S_TUNER -- Get or set tuner attributes
- ioctl VIDIOC_LOG_STATUS -- Log driver status information
- ioctl VIDIOC_OVERLAY -- Start or stop video overlay
- ioctl VIDIOC_QBUF, VIDIOC_DQBUF -- Exchange a buffer with the driver
- ioctl VIDIOC_QUERYBUF -- Query the status of a buffer
- ioctl VIDIOC_QUERYCAP -- Query device capabilities
- ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU -- Enumerate controls and menu control items
- ioctl VIDIOC_QUERYSTD -- Sense the video standard received by the currentinput
- ioctl VIDIOC_REQBUFS -- Initiate Memory Mapping or User Pointer I/O
- ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF -- Start or stop streaming I/O
- V4L2 mmap() -- Map device memory into application address space
- V4L2 munmap() -- Unmap device memory
- V4L2 open() -- Open a V4L2 device
- V4L2 poll() -- Wait for some event on a file descriptor
- V4L2 read() -- Read from a V4L2 device
- V4L2 select() -- Synchronous I/O multiplexing
- V4L2 write() -- Write to a V4L2 device
V4L2 close()
Description
Closes the device. Any I/O in progress is terminated andresources associated with the file descriptor are freed. However dataformat parameters, current input or output, control values or otherproperties remain unchanged.
Return Value
The function returns 0 onsuccess, -1 on failure and theerrno
is set appropriately. Possible errorcodes:
- EBADF
-
fd
is not a valid open filedescriptor.
V4L2 ioctl()
Arguments
-
fd
-
File descriptor returned by
open()
. -
request
-
V4L2 ioctl request code as defined in the videodev.h header file, for exampleVIDIOC_QUERYCAP.
-
argp
-
Pointer to a function parameter, usually a structure.
Description
The ioctl()
function is used to programV4L2 devices. The argumentfd
must be an openfile descriptor. An ioctlrequest
has encodedin it whether the argument is an input, output or read/writeparameter, and the size of the argumentargp
inbytes. Macros and defines specifying V4L2 ioctl requests are locatedin thevideodev.h header file.Applications should use their own copy, not include the version in thekernel sources on the system they compile on. All V4L2 ioctl requests,their respective function and parameters are specified inReference I,Function Reference.
Return Value
On success the ioctl()
function returns0 and does not reset theerrno
variable. On failure-1 is returned, when the ioctl takes anoutput or read/write parameter it remains unmodified, and theerrno
variable is set appropriately. See below forpossible error codes. Generic errors likeEBADForEFAULT are not listed in the sectionsdiscussing individual ioctl requests.
Note ioctls may return undefined error codes. Since errorsmay have side effects such as a driver reset applications shouldabort on unexpected errors.
- EBADF
-
fd
is not a valid open filedescriptor. - EBUSY
-
The property cannot be changed right now. Typicallythis error code is returned when I/O is in progress or the driversupports multiple opens and another process locked the property.
- EFAULT
-
argp
references an inaccessiblememory area. - ENOTTY
-
fd
is not associated with acharacter special device. - EINVAL
-
The
request
or the data pointedto byargp
is not valid. This is a very commonerror code, see the individual ioctl requests listed inReference I,Function Reference for actual causes. - ENOMEM
-
Not enough physical or virtual memory was available tocomplete the request.
- ERANGE
-
The application attempted to set a control with the
VIDIOC_S_CTRL
ioctl to a value which is out of bounds.
ioctl VIDIOC_CROPCAP
Description
Applications use this function to query the croppinglimits, the pixel aspect of images and to calculate scale factors.They set thetype
field of a v4l2_cropcapstructure to the respective buffer (stream) type and call theVIDIOC_CROPCAP
ioctl with a pointer to thisstructure. Drivers fill the rest of the structure. The results areconstant except when switching the video standard. Remember thisswitch can occur implicit when switching the video input oroutput.
Table 1. struct v4l2_cropcap
enum v4l2_buf_type | type |
Type of the data stream, set by the application.Only these types are valid here:V4L2_BUF_TYPE_VIDEO_CAPTURE ,V4L2_BUF_TYPE_VIDEO_OUTPUT ,V4L2_BUF_TYPE_VIDEO_OVERLAY , and custom (driverdefined) types with code V4L2_BUF_TYPE_PRIVATE and higher. |
struct v4l2_rect | bounds |
Defines the window within capturing or output ispossible, this may exclude for example the horizontal and verticalblanking areas. The cropping rectangle cannot exceed these limits.Width and height are defined in pixels, the driver writer is free tochoose origin and units of the coordinate system in the analogdomain. |
struct v4l2_rect | defrect |
Default cropping rectangle, it shall cover the"whole picture". Assuming pixel aspect 1/1 this could be for example a640 × 480 rectangle for NTSC, a768 × 576 rectangle for PAL and SECAM centered overthe active picture area. The same co-ordinate system as for bounds is used. |
struct v4l2_fract | pixelaspect |
This is the pixel aspect (y / x) when noscaling is applied, the ratio of the actual samplingfrequency and the frequency required to get squarepixels. When cropping coordinates refer to square pixels,the driver sets |
Table 2. struct v4l2_rect
__s32 | left |
Horizontal offset of the top, left corner of therectangle, in pixels. |
__s32 | top |
Vertical offset of the top, left corner of therectangle, in pixels. |
__s32 | width |
Width of the rectangle, in pixels. |
__s32 | height |
Height of the rectangle, in pixels. Widthand height cannot be negative, the fields are signed forhysterical reasons. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_cropcap
type
isinvalid or the ioctl is not supported. This is not permitted forvideo capture, output and overlay devices, which must supportVIDIOC_CROPCAP
.
ioctl VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER
Arguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_DBG_G_REGISTER, VIDIOC_DBG_S_REGISTER
-
argp
-
Description
Experimental: This is an experimentalinterface and may change in the future.
For driver debugging purposes these ioctls allow testapplications to access hardware registers directly. Regularapplications should not use them.
Since writing or even reading registers can jeopardize thesystem security, its stability and damage the hardware, both ioctlsrequire superuser privileges. Additionally the Linux kernel must becompiled with theCONFIG_VIDEO_ADV_DEBUG
optionto enable these ioctls.
To write a register applications must initialize all fieldsof a struct v4l2_register and callVIDIOC_DBG_S_REGISTER
with a pointer to thisstructure. The match_type
andmatch_chip
fields select a chip on the TVcard, thereg
field specifies a registernumber and theval
field the value to bewritten into the register.
To read a register applications must initialize thematch_type
,match_chip
andreg
fields, and callVIDIOC_DBG_G_REGISTER
with a pointer to thisstructure. On success the driver stores the register value in theval
field. On failure the structure remainsunchanged.
When match_type
isV4L2_CHIP_MATCH_HOST
,match_chip
selects the nth non-I2C chipon the TV card. Drivers may also interpretmatch_chip
as a random ID, but we recommendagainst that. The number zero always selects the host chip, e. g. thechip connected to the PCI bus. You can find out which chips arepresent with theVIDIOC_G_CHIP_IDENT
ioctl.
When match_type
isV4L2_CHIP_MATCH_I2C_DRIVER
,match_chip
contains a driver ID as definedin thelinux/i2c-id.h header file. For instanceI2C_DRIVERID_SAA7127
will match any chipsupported by the saa7127 driver, regardless of its I2C bus address.When multiple chips supported by the same driver are present, theeffect of these ioctls is undefined. Again with theVIDIOC_G_CHIP_IDENT
ioctl you can find out which I2C chips arepresent.
When match_type
isV4L2_CHIP_MATCH_I2C_ADDR
,match_chip
selects a chip by its 7 bit I2Cbus address.
Success not guaranteed: Due to a flaw in the Linux I2C bus driver these ioctls mayreturn successfully without actually reading or writing a register. Tocatch the most likely failure we recommend a
VIDIOC_G_CHIP_IDENT
call confirming the presence of the selected I2C chip.
These ioctls are optional, not all drivers may support them.However when a driver supports these ioctls it must also supportVIDIOC_G_CHIP_IDENT
. Conversely it may supportVIDIOC_G_CHIP_IDENT
but not these ioctls.
VIDIOC_DBG_G_REGISTER
andVIDIOC_DBG_S_REGISTER
were introduced in Linux2.6.21.
We recommended the v4l2-dbgutility over calling these ioctls directly. It is available from theLinuxTV v4l-dvb repository; seehttp://linuxtv.org/repo/ foraccess instructions.
Table 1. struct v4l2_register
__u32 | match_type |
See Table 2 for a list of possible types. | |
__u32 | match_chip |
Match a chip by this number, interpreted accordingto the match_type field. |
|
__u64 | reg |
A register number. | |
__u64 | val |
The value read from, or to be written into theregister. |
Table 2. Chip Match Types
V4L2_CHIP_MATCH_HOST |
0 | Match the nth chip on the card, zero for the host chip. Does not match I2C chips. |
V4L2_CHIP_MATCH_I2C_DRIVER |
1 | Match an I2C chip by its driver ID from thelinux/i2c-id.h header file. |
V4L2_CHIP_MATCH_I2C_ADDR |
2 | Match a chip by its 7 bit I2C bus address. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The driver does not support this ioctl, or the kernelwas not compiled with the
CONFIG_VIDEO_ADV_DEBUG
option, or thematch_type
is invalid, or theselected chip or register does not exist. - EPERM
-
Insufficient permissions. Root privileges are requiredto execute these ioctls.
ioctl VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD
Arguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_ENCODER_CMD, VIDIOC_TRY_ENCODER_CMD
-
argp
-
Description
Experimental: This is an experimentalinterface and may change in the future.
These ioctls control an audio/video (usually MPEG-) encoder.VIDIOC_ENCODER_CMD
sends a command to theencoder,VIDIOC_TRY_ENCODER_CMD
can be used totry a command without actually executing it.
To send a command applications must initialize all fields of a struct v4l2_encoder_cmd and callVIDIOC_ENCODER_CMD
orVIDIOC_TRY_ENCODER_CMD
with a pointer to this structure.
The cmd
field must contain thecommand code. Theflags
field is currentlyonly used by the STOP command and contains one bit: If theV4L2_ENC_CMD_STOP_AT_GOP_END
flag is set,encoding will continue until the end of the currentGroupOf Pictures, otherwise it will stop immediately.
A read
() call sends a START command tothe encoder if it has not been started yet. After a STOP command,read
() calls will read the remaining databuffered by the driver. When the buffer is empty,read
() will return zero and the nextread
() call will restart the encoder.
A close
() call sends an immediate STOPto the encoder, and all buffered data is discarded.
These ioctls are optional, not all drivers may supportthem. They were introduced in Linux 2.6.21.
Table 1. struct v4l2_encoder_cmd
__u32 | cmd |
The encoder command, see Table 2. |
__u32 | flags |
Flags to go with the command, see Table 3. If no flags are defined forthis command, drivers and applications must set this field tozero. |
__u32 | data [8] |
Reserved for future extensions. Drivers andapplications must set the array to zero. |
Table 2. Encoder Commands
V4L2_ENC_CMD_START |
0 | Start the encoder. When the encoder is alreadyrunning or paused, this command does nothing. No flags are defined forthis command. |
V4L2_ENC_CMD_STOP |
1 | Stop the encoder. When theV4L2_ENC_CMD_STOP_AT_GOP_END flag is set,encoding will continue until the end of the currentGroupOf Pictures, otherwise encoding will stop immediately.When the encoder is already stopped, this command doesnothing. |
V4L2_ENC_CMD_PAUSE |
2 | Pause the encoder. When the encoder has not beenstarted yet, the driver will return anEPERM error code. When the encoder isalready paused, this command does nothing. No flags are defined forthis command. |
V4L2_ENC_CMD_RESUME |
3 | Resume encoding after a PAUSE command. When theencoder has not been started yet, the driver will return anEPERM error code.When the encoder is already running, this command does nothing. Noflags are defined for this command. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The driver does not support this ioctl, or the
cmd
field is invalid. - EPERM
-
The application sent a PAUSE or RESUME command whenthe encoder was not running.
ioctl VIDIOC_ENUMAUDIO
Description
To query the attributes of an audio input applicationsinitialize the index
field and zero out thereserved
array of a struct v4l2_audioand call theVIDIOC_ENUMAUDIO
ioctl with a pointerto this structure. Drivers fill the rest of the structure or return anEINVAL error code when the index is out of bounds. To enumerate all audioinputs applications shall begin at index zero, incrementing by oneuntil the driver returnsEINVAL.
See ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO(2) for a description ofstruct v4l2_audio.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The number of the audio input is out of bounds, orthere are no audio inputs at all and this ioctl is notsupported.
ioctl VIDIOC_ENUMAUDOUT
Description
To query the attributes of an audio output applicationsinitialize the index
field and zero out thereserved
array of a struct v4l2_audioout andcall theVIDIOC_G_AUDOUT
ioctl with a pointerto this structure. Drivers fill the rest of the structure or return anEINVAL error code when the index is out of bounds. To enumerate all audiooutputs applications shall begin at index zero, incrementing by oneuntil the driver returns EINVAL.
Note connectors on a TV card to loop back the received audiosignal to a sound card are not audio outputs in this sense.
See ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT(2) for a description ofstruct v4l2_audioout.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The number of the audio output is out of bounds, orthere are no audio outputs at all and this ioctl is notsupported.
ioctl VIDIOC_ENUM_FMT
Description
To enumerate image formats applications initialize thetype
andindex
field of struct v4l2_fmtdesc and call theVIDIOC_ENUM_FMT
ioctl with a pointer to thisstructure. Drivers fill the rest of the structure or return anEINVAL error code. All formats are enumerable by beginning at index zero andincrementing by one untilEINVAL isreturned.
Table 1. struct v4l2_fmtdesc
__u32 | index |
Number of the format in the enumeration, set bythe application. This is in no way related to thepixelformat field. |
enum v4l2_buf_type | type |
Type of the data stream, set by the application.Only these types are valid here:V4L2_BUF_TYPE_VIDEO_CAPTURE ,V4L2_BUF_TYPE_VIDEO_OUTPUT ,V4L2_BUF_TYPE_VIDEO_OVERLAY , and custom (driverdefined) types with code V4L2_BUF_TYPE_PRIVATE and higher. |
__u32 | flags |
See Table 2 |
__u8 | description [32] |
Description of the format, a NUL-terminated ASCIIstring. This information is intended for the user, for example: "YUV4:2:2". |
__u32 | pixelformat |
The image format identifier. This is afour character code as computed by the v4l2_fourcc()macro: |
#define v4l2_fourcc(a,b,c,d) (((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24)) Several image formats are alreadydefined by this specification in Chapter 2. Note thesecodes are not the same as those used in the Windows world. |
||
__u32 | reserved [4] |
Reserved for future extensions. Drivers must setthe array to zero. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_fmtdesc
type
is not supported or theindex
is out ofbounds.
ioctl VIDIOC_ENUM_FRAMESIZES
Arguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_ENUM_FRAMESIZES
-
argp
-
Pointer to a struct v4l2_frmsizeenum that contains an indexand pixel format and receives a frame width and height.
Description
Experimental: This is an experimentalinterface and may change in the future.
This ioctl allows applications to enumerate all frame sizes(i. e. width and height in pixels) that the device supports for thegiven pixel format.
The supported pixel formats can be obtained by using theVIDIOC_ENUM_FMT
function.
The return value and the content of thev4l2_frmsizeenum.type
field depend on thetype of frame sizes the device supports. Here are the semantics of thefunction for the different cases:
-
Discrete: The functionreturns success if the given index value (zero-based) is valid. Theapplication should increase the index by one for each call until
EINVAL
is returned. Thev4l2_frmsizeenum.type
field is set toV4L2_FRMSIZE_TYPE_DISCRETE
by the driver. Of theunion only thediscrete
member isvalid. -
Step-wise: The functionreturns success if the given index value is zero and
EINVAL
for any other index value. Thev4l2_frmsizeenum.type
field is set toV4L2_FRMSIZE_TYPE_STEPWISE
by the driver. Of theunion only thestepwise
member isvalid. -
Continuous: This is aspecial case of the step-wise type above. The function returns successif the given index value is zero and
EINVAL
forany other index value. Thev4l2_frmsizeenum.type
field is set toV4L2_FRMSIZE_TYPE_CONTINUOUS
by the driver. Ofthe union only thestepwise
member is validand thestep_width
andstep_height
values are set to 1.
When the application calls the function with index zero, itmust check the type
field to determine thetype of frame size enumeration the device supports. Only for theV4L2_FRMSIZE_TYPE_DISCRETE
type does it makesense to increase the index value to receive more frame sizes.
Note that the order in which the frame sizes are returnedhas no special meaning. In particular does it not say anything aboutpotential default format sizes.
Applications can assume that the enumeration data does notchange without any interaction from the application itself. This meansthat the enumeration data is consistent if the application does notperform any other ioctl calls while it runs the frame sizeenumeration.
Structs
In the structs below, IN denotes avalue that has to be filled in by the application,OUT denotes values that the driver fills in. Theapplication should zero out all members except for theIN fields.
Table 1. struct v4l2_frmsize_discrete
__u32 | width |
Width of the frame [pixel]. |
__u32 | height |
Height of the frame [pixel]. |
Table 2. struct v4l2_frmsize_stepwise
__u32 | min_width |
Minimum frame width [pixel]. |
__u32 | max_width |
Maximum frame width [pixel]. |
__u32 | step_width |
Frame width step size [pixel]. |
__u32 | min_height |
Minimum frame height [pixel]. |
__u32 | max_height |
Maximum frame height [pixel]. |
__u32 | step_height |
Frame height step size [pixel]. |
Table 3. struct v4l2_frmsizeenum
__u32 | index |
IN: Index of the given frame size in the enumeration. | |
__u32 | pixel_format |
IN: Pixel format for which the frame sizes are enumerated. | |
__u32 | type |
OUT: Frame size type the device supports. | |
union | OUT: Frame size with the given index. | ||
struct v4l2_frmsize_discrete | discrete |
||
struct v4l2_frmsize_stepwise | stepwise |
||
__u32 | reserved[2] |
Reserved space for future use. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
See the description section above for a list of returnvalues that errno
can have.
ioctl VIDIOC_ENUM_FRAMEINTERVALS
Arguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_ENUM_FRAMEINTERVALS
-
argp
-
Pointer to a struct v4l2_frmivalenum structure thatcontains a pixel format and size and receives a frame interval.
Description
This ioctl allows applications to enumerate all frameintervals that the device supports for the given pixel format andframe size.
The supported pixel formats and frame sizes can be obtainedby using the VIDIOC_ENUM_FMT
and VIDIOC_ENUM_FRAMESIZES
functions.
The return value and the content of thev4l2_frmivalenum.type
field depend on thetype of frame intervals the device supports. Here are the semantics ofthe function for the different cases:
-
Discrete: The functionreturns success if the given index value (zero-based) is valid. Theapplication should increase the index by one for each call until
EINVAL
is returned. The `v4l2_frmivalenum.type`field is set to `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of theunion only the `discrete` member is valid. -
Step-wise: The functionreturns success if the given index value is zero and
EINVAL
for any other index value. Thev4l2_frmivalenum.type
field is set toV4L2_FRMIVAL_TYPE_STEPWISE
by the driver. Of theunion only thestepwise
member isvalid. -
Continuous: This is aspecial case of the step-wise type above. The function returns successif the given index value is zero and
EINVAL
forany other index value. Thev4l2_frmivalenum.type
field is set toV4L2_FRMIVAL_TYPE_CONTINUOUS
by the driver. Ofthe union only thestepwise
member is validand thestep
value is set to 1.
When the application calls the function with index zero, itmust check the type
field to determine thetype of frame interval enumeration the device supports. Only for theV4L2_FRMIVAL_TYPE_DISCRETE
type does it makesense to increase the index value to receive more frameintervals.
Note that the order in which the frame intervals arereturned has no special meaning. In particular does it not sayanything about potential default frame intervals.
Applications can assume that the enumeration data does notchange without any interaction from the application itself. This meansthat the enumeration data is consistent if the application does notperform any other ioctl calls while it runs the frame intervalenumeration.
Notes
-
Frame intervals and framerates: The V4L2 API uses frame intervals instead of framerates. Given the frame interval the frame rate can be computed asfollows:
frame_rate = 1 / frame_interval
Structs
In the structs below, IN denotes avalue that has to be filled in by the application,OUT denotes values that the driver fills in. Theapplication should zero out all members except for theIN fields.
Table 1. struct v4l2_frmival_stepwise
struct v4l2_fract | min |
Minimum frame interval [s]. |
struct v4l2_fract | max |
Maximum frame interval [s]. |
struct v4l2_fract | step |
Frame interval step size [s]. |
Table 2. struct v4l2_frmivalenum
__u32 | index |
IN: Index of the given frame interval in theenumeration. | |
__u32 | pixel_format |
IN: Pixel format for which the frame intervals areenumerated. | |
__u32 | width |
IN: Frame width for which the frame intervals areenumerated. | |
__u32 | height |
IN: Frame height for which the frame intervals areenumerated. | |
__u32 | type |
OUT: Frame interval type the device supports. | |
union | OUT: Frame interval with the given index. | ||
struct v4l2_fract | discrete |
Frame interval [s]. | |
struct v4l2_frmival_stepwise | stepwise |
||
__u32 | reserved[2] |
Reserved space for future use. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
See the description section above for a list of returnvalues that errno
can have.
ioctl VIDIOC_ENUMINPUT
Description
To query the attributes of a video input applicationsinitialize the index
field of struct v4l2_inputand call theVIDIOC_ENUMINPUT
ioctl with apointer to this structure. Drivers fill the rest of the structure orreturn anEINVAL error code when the index is out of bounds. To enumerate allinputs applications shall begin at index zero, incrementing by oneuntil the driver returnsEINVAL.
Table 1. struct v4l2_input
__u32 | index |
Identifies the input, set by theapplication. |
__u8 | name [32] |
Name of the video input, a NUL-terminated ASCIIstring, for example: "Vin (Composite 2)". This information is intendedfor the user, preferably the connector label on the device itself. |
__u32 | type |
Type of the input, see Table 2. |
__u32 | audioset |
Drivers can enumerate up to 32 video andaudio inputs. This field shows which audio inputs were selectable asaudio source if this was the currently selected video input. It is abit mask. The LSB corresponds to audio input 0, the MSB to input 31.Any number of bits can be set, or none. When the driverdoes not enumerate audio inputs no bits must be set. Applicationsshall not interpret this as lack of audio support. Some driversautomatically select audio sources and do not enumerate them sincethere is no choice anyway. For details on audio inputs andhow to select the current input see Section 1.5. |
__u32 | tuner |
Capture devices can have zero or more tuners (RFdemodulators). When the type is set toV4L2_INPUT_TYPE_TUNER this is an RF connector andthis field identifies the tuner. It corresponds tostruct v4l2_tuner fieldindex . For details ontuners see Section 1.6. |
v4l2_std_id | std |
Every video input supports one or more differentvideo standards. This field is a set of all supported standards. Fordetails on video standards and how to switch seeSection 1.7. |
__u32 | status |
This field provides status information about theinput. See Table 3 for flags.status is only valid when this is thecurrent input. |
__u32 | reserved [4] |
Reserved for future extensions. Drivers must setthe array to zero. |
Table 2. Input Types
V4L2_INPUT_TYPE_TUNER |
1 | This input uses a tuner (RF demodulator). |
V4L2_INPUT_TYPE_CAMERA |
2 | Analog baseband input, for example CVBS /Composite Video, S-Video, RGB. |
Table 3. Input Status Flags
General | ||
V4L2_IN_ST_NO_POWER |
0x00000001 | Attached device is off. |
V4L2_IN_ST_NO_SIGNAL |
0x00000002 | |
V4L2_IN_ST_NO_COLOR |
0x00000004 | The hardware supports color decoding, but does notdetect color modulation in the signal. |
Analog Video | ||
V4L2_IN_ST_NO_H_LOCK |
0x00000100 | No horizontal sync lock. |
V4L2_IN_ST_COLOR_KILL |
0x00000200 | A color killer circuit automatically disables colordecoding when it detects no color modulation. When this flag is setthe color killer is enabledand has shut offcolor decoding. |
Digital Video | ||
V4L2_IN_ST_NO_SYNC |
0x00010000 | No synchronization lock. |
V4L2_IN_ST_NO_EQU |
0x00020000 | No equalizer lock. |
V4L2_IN_ST_NO_CARRIER |
0x00040000 | Carrier recovery failed. |
VCR and Set-Top Box | ||
V4L2_IN_ST_MACROVISION |
0x01000000 | Macrovision is an analog copy prevention systemmangling the video signal to confuse video recorders. When thisflag is set Macrovision has been detected. |
V4L2_IN_ST_NO_ACCESS |
0x02000000 | Conditional access denied. |
V4L2_IN_ST_VTR |
0x04000000 | VTR time constant. [?] |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_input
index
isout of bounds.
ioctl VIDIOC_ENUMOUTPUT
Description
To query the attributes of a video outputs applicationsinitialize the index
field of struct v4l2_outputand call theVIDIOC_ENUMOUTPUT
ioctl with apointer to this structure. Drivers fill the rest of the structure orreturn anEINVAL error code when the index is out of bounds. To enumerate alloutputs applications shall begin at index zero, incrementing by oneuntil the driver returnsEINVAL.
Table 1. struct v4l2_output
__u32 | index |
Identifies the output, set by theapplication. |
__u8 | name [32] |
Name of the video output, a NUL-terminated ASCIIstring, for example: "Vout". This information is intended for theuser, preferably the connector label on the device itself. |
__u32 | type |
Type of the output, see Table 2. |
__u32 | audioset |
Drivers can enumerate up to 32 video andaudio outputs. This field shows which audio outputs wereselectable as the current output if this was the currently selectedvideo output. It is a bit mask. The LSB corresponds to audio output 0,the MSB to output 31. Any number of bits can be set, ornone. When the driver does not enumerate audio outputs nobits must be set. Applications shall not interpret this as lack ofaudio support. Drivers may automatically select audio outputs withoutenumerating them. For details on audio outputs and how toselect the current output see Section 1.5. |
__u32 | modulator |
Output devices can have zero or more RF modulators.When the type isV4L2_OUTPUT_TYPE_MODULATOR this is an RFconnector and this field identifies the modulator. It corresponds tostruct v4l2_modulator fieldindex . For detailson modulators see Section 1.6. |
v4l2_std_id | std |
Every video output supports one or more differentvideo standards. This field is a set of all supported standards. Fordetails on video standards and how to switch seeSection 1.7. |
__u32 | reserved [4] |
Reserved for future extensions. Drivers must setthe array to zero. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_output
index
is out of bounds.
ioctl VIDIOC_ENUMSTD
Description
To query the attributes of a video standard,especially a custom (driver defined) one, applications initialize theindex
field of struct v4l2_standard and call theVIDIOC_ENUMSTD
ioctl with a pointer to thisstructure. Drivers fill the rest of the structure or return anEINVAL error code when the index is out of bounds. To enumerate all standardsapplications shall begin at index zero, incrementing by one until thedriver returns EINVAL. Drivers may enumerate adifferent set of standards after switching the video input oroutput.[23]
Table 1. struct v4l2_standard
__u32 | index |
Number of the video standard, set by theapplication. |
v4l2_std_id | id |
The bits in this field identify the standard asone of the common standards listed inTable 3,or if bits 32 to 63 are set as custom standards. Multiple bits can beset if the hardware does not distinguish between these standards,however separate indices do not indicate the opposite. Theid must be unique. No other enumeratedv4l2_standard structure, for this input oroutput anyway, can contain the same set of bits. |
__u8 | name [24] |
Name of the standard, a NUL-terminated ASCIIstring, for example: "PAL-B/G", "NTSC Japan". This information isintended for the user. |
struct v4l2_fract | frameperiod |
The frame period (not field period) is numerator/ denominator. For example M/NTSC has a frame period of 1001 /30000 seconds. |
__u32 | framelines |
Total lines per frame including blanking,e. g. 625 for B/PAL. |
__u32 | reserved [4] |
Reserved for future extensions. Drivers must setthe array to zero. |
Table 3. typedef v4l2_std_id
__u64 | v4l2_std_id |
This type is a set, each bit representing anothervideo standard as listed below and inTable 4. The 32 most significant bits are reservedfor custom (driver defined) video standards. |
#define V4L2_STD_PAL_B ((v4l2_std_id)0x00000001) #define V4L2_STD_PAL_B1 ((v4l2_std_id)0x00000002) #define V4L2_STD_PAL_G ((v4l2_std_id)0x00000004) #define V4L2_STD_PAL_H ((v4l2_std_id)0x00000008) #define V4L2_STD_PAL_I ((v4l2_std_id)0x00000010) #define V4L2_STD_PAL_D ((v4l2_std_id)0x00000020) #define V4L2_STD_PAL_D1 ((v4l2_std_id)0x00000040) #define V4L2_STD_PAL_K ((v4l2_std_id)0x00000080) #define V4L2_STD_PAL_M ((v4l2_std_id)0x00000100) #define V4L2_STD_PAL_N ((v4l2_std_id)0x00000200) #define V4L2_STD_PAL_Nc ((v4l2_std_id)0x00000400) #define V4L2_STD_PAL_60 ((v4l2_std_id)0x00000800)
V4L2_STD_PAL_60
isa hybrid standard with 525 lines, 60 Hz refresh rate, and PAL colormodulation with a 4.43 MHz color subcarrier. Some PAL video recorderscan play back NTSC tapes in this mode for display on a 50/60 Hz agnosticPAL TV.
#define V4L2_STD_NTSC_M ((v4l2_std_id)0x00001000) #define V4L2_STD_NTSC_M_JP ((v4l2_std_id)0x00002000) #define V4L2_STD_NTSC_443 ((v4l2_std_id)0x00004000)
V4L2_STD_NTSC_443
is a hybrid standard with 525 lines, 60 Hz refresh rate, and NTSCcolor modulation with a 4.43 MHz colorsubcarrier.
#define V4L2_STD_NTSC_M_KR ((v4l2_std_id)0x00008000) #define V4L2_STD_SECAM_B ((v4l2_std_id)0x00010000) #define V4L2_STD_SECAM_D ((v4l2_std_id)0x00020000) #define V4L2_STD_SECAM_G ((v4l2_std_id)0x00040000) #define V4L2_STD_SECAM_H ((v4l2_std_id)0x00080000) #define V4L2_STD_SECAM_K ((v4l2_std_id)0x00100000) #define V4L2_STD_SECAM_K1 ((v4l2_std_id)0x00200000) #define V4L2_STD_SECAM_L ((v4l2_std_id)0x00400000) #define V4L2_STD_SECAM_LC ((v4l2_std_id)0x00800000) /* ATSC/HDTV */ #define V4L2_STD_ATSC_8_VSB ((v4l2_std_id)0x01000000) #define V4L2_STD_ATSC_16_VSB ((v4l2_std_id)0x02000000)
V4L2_STD_ATSC_8_VSB
andV4L2_STD_ATSC_16_VSB
are U.S. terrestrial digitalTV standards. Presently the V4L2 API does not support digital TV. Seealso the Linux DVB API athttp://linuxtv.org.
#define V4L2_STD_PAL_BG (V4L2_STD_PAL_B |\ V4L2_STD_PAL_B1 |\ V4L2_STD_PAL_G) #define V4L2_STD_B (V4L2_STD_PAL_B |\ V4L2_STD_PAL_B1 |\ V4L2_STD_SECAM_B) #define V4L2_STD_GH (V4L2_STD_PAL_G |\ V4L2_STD_PAL_H |\ V4L2_STD_SECAM_G |\ V4L2_STD_SECAM_H) #define V4L2_STD_PAL_DK (V4L2_STD_PAL_D |\ V4L2_STD_PAL_D1 |\ V4L2_STD_PAL_K) #define V4L2_STD_PAL (V4L2_STD_PAL_BG |\ V4L2_STD_PAL_DK |\ V4L2_STD_PAL_H |\ V4L2_STD_PAL_I) #define V4L2_STD_NTSC (V4L2_STD_NTSC_M |\ V4L2_STD_NTSC_M_JP |\ V4L2_STD_NTSC_M_KR) #define V4L2_STD_MN (V4L2_STD_PAL_M |\ V4L2_STD_PAL_N |\ V4L2_STD_PAL_Nc |\ V4L2_STD_NTSC) #define V4L2_STD_SECAM_DK (V4L2_STD_SECAM_D |\ V4L2_STD_SECAM_K |\ V4L2_STD_SECAM_K1) #define V4L2_STD_DK (V4L2_STD_PAL_DK |\ V4L2_STD_SECAM_DK) #define V4L2_STD_SECAM (V4L2_STD_SECAM_B |\ V4L2_STD_SECAM_G |\ V4L2_STD_SECAM_H |\ V4L2_STD_SECAM_DK |\ V4L2_STD_SECAM_L |\ V4L2_STD_SECAM_LC) #define V4L2_STD_525_60 (V4L2_STD_PAL_M |\ V4L2_STD_PAL_60 |\ V4L2_STD_NTSC |\ V4L2_STD_NTSC_443) #define V4L2_STD_625_50 (V4L2_STD_PAL |\ V4L2_STD_PAL_N |\ V4L2_STD_PAL_Nc |\ V4L2_STD_SECAM) #define V4L2_STD_UNKNOWN 0 #define V4L2_STD_ALL (V4L2_STD_525_60 |\ V4L2_STD_625_50)
Table 4. Video Standards (based on [ITU BT.470])
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_standard
index
is out of bounds.
ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO
Description
To query the current audio input applications zero out thereserved
array of a struct v4l2_audioand call theVIDIOC_G_AUDIO
ioctl with a pointerto this structure. Drivers fill the rest of the structure or return anEINVAL error code when the device has no audio inputs, or none which combinewith the current video input.
Audio inputs have one writable property, the audio mode. Toselect the current audio inputand change theaudio mode, applications initialize theindex
andmode
fields, and thereserved
array of av4l2_audio
structure and call theVIDIOC_S_AUDIO
ioctl. Drivers may switch to adifferent audio mode if the request cannot be satisfied. However, thisis a write-only ioctl, it does not return the actual new audiomode.
Table 1. struct v4l2_audio
__u32 | index |
Identifies the audio input, set by thedriver or application. |
__u8 | name [32] |
Name of the audio input, a NUL-terminated ASCIIstring, for example: "Line In". This information is intended for theuser, preferably the connector label on the device itself. |
__u32 | capability |
Audio capability flags, see Table 2. |
__u32 | mode |
Audio mode flags set by drivers and applications (on VIDIOC_S_AUDIO ioctl), seeTable 3. |
__u32 | reserved [2] |
Reserved for future extensions. Drivers andapplications must set the array to zero. |
Table 2. Audio Capability Flags
V4L2_AUDCAP_STEREO |
0x00001 | This is a stereo input. The flag is intended toautomatically disable stereo recording etc. when the signal is alwaysmonaural. The API provides no means to detect if stereo isreceived, unless the audio input belongs to atuner. |
V4L2_AUDCAP_AVL |
0x00002 | Automatic Volume Level mode is supported. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
No audio inputs combine with the current video input,or the number of the selected audio input is out of bounds or it doesnot combine, or there are no audio inputs at all and the ioctl is notsupported.
- EBUSY
-
I/O is in progress, the input cannot beswitched.
ioctl VIDIOC_G_AUDOUT, VIDIOC_S_AUDOUT
Description
To query the current audio output applications zero out thereserved
array of a struct v4l2_audioout andcall theVIDIOC_G_AUDOUT
ioctl with a pointerto this structure. Drivers fill the rest of the structure or return anEINVAL error code when the device has no audio inputs, or none which combinewith the current video output.
Audio outputs have no writable properties. Nevertheless, toselect the current audio output applications can initialize theindex
field andreserved
array (which in the future maycontain writable properties) of av4l2_audioout
structure and call theVIDIOC_S_AUDOUT
ioctl. Drivers switch to therequested output or return theEINVAL error code when the index is out ofbounds. This is a write-only ioctl, it does not return the currentaudio output attributes asVIDIOC_G_AUDOUT
does.
Note connectors on a TV card to loop back the received audiosignal to a sound card are not audio outputs in this sense.
Table 1. struct v4l2_audioout
__u32 | index |
Identifies the audio output, set by thedriver or application. |
__u8 | name [32] |
Name of the audio output, a NUL-terminated ASCIIstring, for example: "Line Out". This information is intended for theuser, preferably the connector label on the device itself. |
__u32 | capability |
Audio capability flags, none defined yet. Driversmust set this field to zero. |
__u32 | mode |
Audio mode, none defined yet. Drivers andapplications (on VIDIOC_S_AUDOUT ) must set thisfield to zero. |
__u32 | reserved [2] |
Reserved for future extensions. Drivers andapplications must set the array to zero. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
No audio outputs combine with the current videooutput, or the number of the selected audio output is out of bounds orit does not combine, or there are no audio outputs at all and theioctl is not supported.
- EBUSY
-
I/O is in progress, the output cannot beswitched.
ioctl VIDIOC_G_CHIP_IDENT
Description
Experimental: This is an experimental interface and may change inthe future.
For driver debugging purposes this ioctl allows testapplications to query the driver about the chips present on the TVcard. Regular applications should not use it. When you found a chipspecific bug, please contact the Video4Linux mailing list (https://listman.redhat.com/mailman/listinfo/video4linux-list)so it can be fixed.
To query the driver applications must initialize thematch_type
andmatch_chip
fields of a struct v4l2_chip_identand call VIDIOC_G_CHIP_IDENT
with a pointer tothis structure. On success the driver stores information about theselected chip in theident
andrevision
fields. On failure the structureremains unchanged.
When match_type
isV4L2_CHIP_MATCH_HOST
,match_chip
selects the nth non-I2C chipon the TV card. You can enumerate all chips by starting at zero andincrementingmatch_chip
by one untilVIDIOC_G_CHIP_IDENT
fails with anEINVAL error code.Drivers may also interpretmatch_chip
as arandom ID, but we recommend against that. The number zero alwaysselects the host chip, e. g. the chip connected to the PCI bus.
When match_type
isV4L2_CHIP_MATCH_I2C_DRIVER
,match_chip
contains a driver ID as definedin thelinux/i2c-id.h header file. For instanceI2C_DRIVERID_SAA7127
will match any chipsupported by the saa7127 driver, regardless of its I2C bus address.When multiple chips supported by the same driver are present, theioctl will returnV4L2_IDENT_AMBIGUOUS
in theident
field.
When match_type
isV4L2_CHIP_MATCH_I2C_ADDR
,match_chip
selects a chip by its 7 bitI2C bus address.
On success, the ident
field willcontain a chip ID from the Linuxmedia/v4l2-chip-ident.h header file, and therevision
field will contain a driverspecific value, or zero if no particular revision is associated withthis chip.
When the driver could not identify the selected chip,ident
will containV4L2_IDENT_UNKNOWN
. When no chip matchedmatch_type
andmatch_chip
, the ioctl will succeed but theident
field will containV4L2_IDENT_NONE
. If multiple chips matched,ident
will containV4L2_IDENT_AMBIGUOUS
. In all these cases therevision
field remains unchanged.
This ioctl is optional, not all drivers may support it. Itwas introduced in Linux 2.6.21.
We recommended the v4l2-dbgutility over calling this ioctl directly. It is available from theLinuxTV v4l-dvb repository; seehttp://linuxtv.org/repo/ foraccess instructions.
Table 1. struct v4l2_chip_ident
__u32 | match_type |
See Table 2 for a list ofpossible types. |
__u32 | match_chip |
Match a chip by this number, interpreted accordingto the match_type field. |
__u32 | ident |
A chip identifier as defined in the Linuxmedia/v4l2-chip-ident.h header file, or one ofthe values fromTable 3. |
__u32 | revision |
A chip revision, chip and driver specific. |
Table 2. Chip Match Types
V4L2_CHIP_MATCH_HOST |
0 | Match the nth chip on the card, zero for the host chip. Does not match I2C chips. |
V4L2_CHIP_MATCH_I2C_DRIVER |
1 | Match an I2C chip by its driver ID from thelinux/i2c-id.h header file. |
V4L2_CHIP_MATCH_I2C_ADDR |
2 | Match a chip by its 7 bit I2C bus address. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The driver does not support this ioctl, or the
match_type
is invalid.
ioctl VIDIOC_G_CROP, VIDIOC_S_CROP
Description
To query the cropping rectangle size and positionapplications set the type
field of av4l2_crop
structure to the respective buffer(stream) type and call theVIDIOC_G_CROP
ioctlwith a pointer to this structure. The driver fills the rest of thestructure or returns theEINVAL error code if cropping is not supported.
To change the cropping rectangle applications initialize thetype
and struct v4l2_rect substructure namedc
of a v4l2_crop structure and call theVIDIOC_S_CROP
ioctl with a pointer to thisstructure.
The driver first adjusts the requested dimensions againsthardware limits, i. e. the bounds given by the capture/output window,and it rounds to the closest possible values of horizontal andvertical offset, width and height. In particular the driver must roundthe vertical offset of the cropping rectangle to frame lines modulotwo, such that the field order cannot be confused.
Second the driver adjusts the image size (the oppositerectangle of the scaling process, source or target depending on thedata direction) to the closest size possible while maintaining thecurrent horizontal and vertical scaling factor.
Finally the driver programs the hardware with the actualcropping and image parameters.VIDIOC_S_CROP
is awrite-only ioctl, it does not return the actual parameters. To querythem applications must callVIDIOC_G_CROP
andVIDIOC_G_FMT
. When the parameters are unsuitable the application maymodify the cropping or image parameters and repeat the cycle untilsatisfactory parameters have been negotiated.
When cropping is not supported then no parameters arechanged and VIDIOC_S_CROP
returns theEINVAL error code.
Table 1. struct v4l2_crop
enum v4l2_buf_type | type |
Type of the data stream, set by the application.Only these types are valid here:V4L2_BUF_TYPE_VIDEO_CAPTURE ,V4L2_BUF_TYPE_VIDEO_OUTPUT ,V4L2_BUF_TYPE_VIDEO_OVERLAY , and custom (driverdefined) types with codeV4L2_BUF_TYPE_PRIVATE and higher. |
struct v4l2_rect | c |
Cropping rectangle. The same co-ordinate system asfor struct v4l2_cropcapbounds is used. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
Cropping is not supported.
ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
Description
To get the current value of a control applicationsinitialize the id
field of a structv4l2_control
and call theVIDIOC_G_CTRL
ioctl with a pointer to thisstructure. To change the value of a control applications initializetheid
and value
fields of a structv4l2_control
and call theVIDIOC_S_CTRL
ioctl.
When the id
is invalid driversreturn an EINVAL error code. When the value
is outof bounds drivers can choose to take the closest valid value or returnanERANGE error code, whatever seems more appropriate. However,VIDIOC_S_CTRL
is a write-only ioctl, it does notreturn the actual new value.
These ioctls work only with user controls. For othercontrol classes the VIDIOC_G_EXT_CTRLS
, VIDIOC_S_EXT_CTRLS
orVIDIOC_TRY_EXT_CTRLS
must be used.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_control
id
isinvalid. - ERANGE
-
The struct v4l2_control
value
is out of bounds. - EBUSY
-
The control is temporarily not changeable, possiblybecause another applications took over control of the device functionthis control belongs to.
ioctl VIDIOC_G_ENC_INDEX
Description
Experimental: This is an experimentalinterface and may change in the future.
The VIDIOC_G_ENC_INDEX
ioctl providesmeta data about a compressed video stream the same or anotherapplication currently reads from the driver, which is useful forrandom access into the stream without decoding it.
To read the data applications must callVIDIOC_G_ENC_INDEX
with a pointer to astruct v4l2_enc_idx. On success the driver fills theentry
array, stores the number of elementswritten in the entries
field, andinitializes theentries_cap
field.
Each element of the entry
arraycontains meta data about one picture. AVIDIOC_G_ENC_INDEX
call reads up toV4L2_ENC_IDX_ENTRIES
entries from a driverbuffer, which can hold up to entries_cap
entries. This number can be lower or higher thanV4L2_ENC_IDX_ENTRIES
, but not zero. When theapplication fails to read the meta data in time the oldest entrieswill be lost. When the buffer is empty or no capturing/encoding is inprogress, entries
will be zero.
Currently this ioctl is only defined for MPEG-2 programstreams and video elementary streams.
Table 1. struct v4l2_enc_idx
__u32 | entries |
The number of entries the driver stored in theentry array. |
||
__u32 | entries_cap |
The number of entries the driver canbuffer. Must be greater than zero. | ||
__u32 | reserved [4] |
Reserved for future extensions.Drivers must set the array to zero. | ||
struct v4l2_enc_idx_entry | entry [V4L2_ENC_IDX_ENTRIES ] |
Meta data about a compressed video stream. Eachelement of the array corresponds to one picture, sorted in ascendingorder by theiroffset . |
Table 2. struct v4l2_enc_idx_entry
__u64 | offset |
The offset in bytes from the beginning of thecompressed video stream to the beginning of this picture, that is aPES packet header as defined inISO 13818-1 or apictureheader as defined in ISO 13818-2. Whenthe encoder is stopped, the driver resets the offset to zero. |
__u64 | pts |
The 33 bit Presentation TimeStamp of this picture as defined inISO 13818-1. |
__u32 | length |
The length of this picture in bytes. |
__u32 | flags |
Flags containing the coding type of this picture, see Table 3. |
__u32 | reserved [2] |
Reserved for future extensions.Drivers must set the array to zero. |
Table 3. Index Entry Flags
V4L2_ENC_IDX_FRAME_I |
0x00 | This is an Intra-coded picture. |
V4L2_ENC_IDX_FRAME_P |
0x01 | This is a Predictive-coded picture. |
V4L2_ENC_IDX_FRAME_B |
0x02 | This is a Bidirectionally predictive-codedpicture. |
V4L2_ENC_IDX_FRAME_MASK |
0x0F | AND the flags field withthis mask to obtain the picture coding type. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The driver does not support this ioctl.
ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,VIDIOC_TRY_EXT_CTRLS
Name
VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS, VIDIOC_TRY_EXT_CTRLS -- Get or set the value of several controls, try controlvaluesArguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,VIDIOC_TRY_EXT_CTRLS
-
argp
-
Description
These ioctls allow the caller to get or set multiplecontrols atomically. Control IDs are grouped into control classes (seeTable 3) and all controls in the control arraymust belong to the same control class.
Applications must always fill in thecount
,ctrl_class
,controls
andreserved
fields of struct v4l2_ext_controls, andinitialize the struct v4l2_ext_control array pointed to by thecontrols
fields.
To get the current value of a set of controls applicationsinitialize the id
field of eachstruct v4l2_ext_control and call theVIDIOC_G_EXT_CTRLS
ioctl.
To change the value of a set of controls applicationsinitialize the id
andvalue
fields of a struct v4l2_ext_control andcall theVIDIOC_S_EXT_CTRLS
ioctl. The controlswill only be set ifall control values arevalid.
To check if the a set of controls have correct valuesapplications initialize theid
andvalue
fields of a struct v4l2_ext_control andcall theVIDIOC_TRY_EXT_CTRLS
ioctl. It is up tothe driver whether wrong values are automatically adjusted to a validvalue or if an error is returned.
When the id
orctrl_class
is invalid drivers return anEINVAL error code. When the value is out of bounds drivers can choose to takethe closest valid value or return an ERANGE error code, whatever seems moreappropriate. In the first case the new value is set instruct v4l2_ext_control.
The driver will only set/get these controls if all controlvalues are correct. This prevents the situation where only some of thecontrols were set/get. Only low-level errors (e. g. a failed i2ccommand) can still cause this situation.
Table 1. struct v4l2_ext_control
__u32 | id |
Identifies the control, set by theapplication. | |
__u32 | reserved2 [2] |
Reserved for future extensions. Drivers andapplications must set the array to zero. | |
union | (anonymous) | ||
__s32 | value |
New value or current value. | |
__s64 | value64 |
New value or current value. | |
void * | reserved |
Reserved for future pointer-type controls. Currently unused. |
Table 2. struct v4l2_ext_controls
__u32 | ctrl_class |
The control class to which all controls belong, seeTable 3. |
__u32 | count |
The number of controls in the controls array. Mayalso be zero. |
__u32 | error_idx |
Set by the driver in case of an error. It is theindex of the control causing the error or equal to 'count' when theerror is not associated with a particular control. Undefined when theioctl returns 0 (success). |
__u32 | reserved [2] |
Reserved for future extensions. Drivers andapplications must set the array to zero. |
struct v4l2_ext_control * | controls |
Pointer to an array ofcount v4l2_ext_control structures. Ignoredifcount equals zero. |
Table 3. Control classes
V4L2_CTRL_CLASS_USER |
0x980000 | The class containing user controls. These controlsare described in Section 1.8. All controls that can be setusing the VIDIOC_S_CTRL and VIDIOC_G_CTRL ioctl belong to thisclass. |
V4L2_CTRL_CLASS_MPEG |
0x990000 | The class containing MPEG compression controls.These controls are described in sectionSection 1.9.5. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_ext_control
id
is invalid or the struct v4l2_ext_controlsctrl_class
is invalid. This error code isalso returned by theVIDIOC_S_EXT_CTRLS
andVIDIOC_TRY_EXT_CTRLS
ioctls if two or morecontrol values are in conflict. - ERANGE
-
The struct v4l2_ext_control
value
is out of bounds. - EBUSY
-
The control is temporarily not changeable, possiblybecause another applications took over control of the device functionthis control belongs to.
ioctl VIDIOC_G_FBUF, VIDIOC_S_FBUF
Description
Applications can use the VIDIOC_G_FBUF
andVIDIOC_S_FBUF
ioctl to get and set theframebuffer parameters for aVideoOverlay orVideo Output Overlay(OSD). The type of overlay is implied by the device type (capture oroutput device) and can be determined with theVIDIOC_QUERYCAP
ioctl.One/dev/videoN device must not support bothkinds of overlay.
The V4L2 API distinguishes destructive and non-destructiveoverlays. A destructive overlay copies captured video images into thevideo memory of a graphics card. A non-destructive overlay blendsvideo images into a VGA signal or graphics into a video signal.Video Output Overlays are alwaysnon-destructive.
To get the current parameters applications call theVIDIOC_G_FBUF
ioctl with a pointer to av4l2_framebuffer
structure. The driver fillsall fields of the structure or returns anEINVAL error code when overlays arenot supported.
To set the parameters for a Video OutputOverlay, applications must initialize theflags
field of a structv4l2_framebuffer
. Since the framebuffer isimplemented on the TV card all other parameters are determined by thedriver. When an application callsVIDIOC_S_FBUF
with a pointer to this structure, the driver prepares for the overlayand returns the framebuffer parameters asVIDIOC_G_FBUF
does, or it returns an errorcode.
To set the parameters for a non-destructiveVideo Overlay, applications must initialize theflags
field, thefmt
substructure, and callVIDIOC_S_FBUF
. Again the driver prepares for theoverlay and returns the framebuffer parameters asVIDIOC_G_FBUF
does, or it returns an errorcode.
For a destructive Video Overlayapplications must additionally provide abase
address. Setting up a DMA to arandom memory location can jeopardize the system security, itsstability or even damage the hardware, therefore only the superusercan set the parameters for a destructive video overlay.
Table 1. struct v4l2_framebuffer
__u32 | capability |
Overlay capability flags set by the driver, seeTable 2. | |
__u32 | flags |
Overlay control flags set by application anddriver, see Table 3 | |
void * | base |
Physical base address of the framebuffer,that is the address of the pixel in the top left corner of theframebuffer.a This field is irrelevant tonon-destructive Video Overlays. Fordestructive Video Overlays applications mustprovide a base address. The driver may accept only base addresseswhich are a multiple of two, four or eight bytes. ForVideo Output Overlays the driver must returna valid base address, so applications can find the corresponding Linuxframebuffer device (seeSection 4.4). |
|
struct v4l2_pix_format | fmt |
Layout of the frame buffer. Thev4l2_pix_format structure is defined inChapter 2, for clarification the fields and acceptable values are listed below: |
|
__u32 | width |
Width of the frame buffer in pixels. | |
__u32 | height |
Height of the frame buffer in pixels. | |
__u32 | pixelformat |
The pixel format of theframebuffer. For non-destructive VideoOverlays this field only defines a format for thestruct v4l2_window For destructive VideoOverlays applications must initialize this field. ForVideo Output Overlays the driver must returna valid format. Usually this is an RGB format (for example |
|
enum v4l2_field | field |
Drivers and applications shall ignore this field.If applicable, the field order is selected with theVIDIOC_S_FMT ioctl, using thefield field ofstruct v4l2_window. |
|
__u32 | bytesperline |
Distance in bytes between the leftmost pixels intwo adjacent lines. | |
This field is irrelevant tonon-destructive VideoOverlays. For destructive VideoOverlays both applications and drivers can set this fieldto request padding bytes at the end of each line. Drivers however mayignore the requested value, returning For Video OutputOverlays the driver must return a validvalue. Video hardware may access padding bytes, thereforethey must reside in accessible memory. Consider for example the casewhere padding bytes after the last line of an image cross a systempage boundary. Capture devices may write padding bytes, the value isundefined. Output devices ignore the contents of paddingbytes. When the image format is planar the |
|||
__u32 | sizeimage |
This field is irrelevant tonon-destructive Video Overlays. Fordestructive Video Overlays applications mustinitialize this field. ForVideo OutputOverlays the driver must return a validformat. Together with |
|
enum v4l2_colorspace | colorspace |
This information supplements thepixelformat and must be set by the driver,seeSection 2.2. |
|
__u32 | priv |
Reserved for additional information about custom(driver defined) formats. When not used drivers and applications mustset this field to zero. | |
Notes: a. A physical base address may not suit allplatforms. GK notes in theory we should pass something like PCI device+ memory region + offset instead. If you encounter problems pleasediscuss on the Video4Linux mailing list:https://listman.redhat.com/mailman/listinfo/video4linux-list. |
Table 2. Frame Buffer Capability Flags
V4L2_FBUF_CAP_EXTERNOVERLAY |
0x0001 | The device is capable of non-destructive overlays.When the driver clears this flag, only destructive overlays aresupported. There are no drivers yet which support both destructive andnon-destructive overlays. |
V4L2_FBUF_CAP_CHROMAKEY |
0x0002 | The device supports clipping by chroma-keying theimages. That is, image pixels replace pixels in the VGA or videosignal only where the latter assume a certain color. Chroma-keyingmakes no sense for destructive overlays. |
V4L2_FBUF_CAP_LIST_CLIPPING |
0x0004 | The device supports clipping using a list of cliprectangles. |
V4L2_FBUF_CAP_BITMAP_CLIPPING |
0x0008 | The device supports clipping using a bit mask. |
V4L2_FBUF_CAP_LOCAL_ALPHA |
0x0010 | The device supports clipping/blending using thealpha channel of the framebuffer or VGA signal. Alpha blending makesno sense for destructive overlays. |
V4L2_FBUF_CAP_GLOBAL_ALPHA |
0x0020 | The device supports alpha blending using a globalalpha value. Alpha blending makes no sense for destructive overlays. |
V4L2_FBUF_CAP_LOCAL_INV_ALPHA |
0x0040 | The device supports clipping/blending using theinverted alpha channel of the framebuffer or VGA signal. Alphablending makes no sense for destructive overlays. |
Table 3. Frame Buffer Flags
V4L2_FBUF_FLAG_PRIMARY |
0x0001 | The framebuffer is the primary graphics surface.In other words, the overlay is destructive. [?] |
V4L2_FBUF_FLAG_OVERLAY |
0x0002 | The frame buffer is an overlay surface the samesize as the capture. [?] |
The purpose ofV4L2_FBUF_FLAG_PRIMARY andV4L2_FBUF_FLAG_OVERLAY was never quite clear.Most drivers seem to ignore these flags. For compatibility with thebttv driver applications should set theV4L2_FBUF_FLAG_OVERLAY flag. |
||
V4L2_FBUF_FLAG_CHROMAKEY |
0x0004 | Use chroma-keying. The chroma-key color isdetermined by the chromakey field ofstruct v4l2_window and negotiated with theVIDIOC_S_FMT ioctl, seeSection 4.2andSection 4.4. |
There are no flags to enableclipping using a list of clip rectangles or a bitmap. These methodsare negotiated with theVIDIOC_S_FMT ioctl, seeSection 4.2 andSection 4.4. |
||
V4L2_FBUF_FLAG_LOCAL_ALPHA |
0x0008 | Use the alpha channel of the framebuffer to clip orblend framebuffer pixels with video images. The blendfunction is: output = framebuffer pixel * alpha + video pixel * (1 -alpha). The actual alpha depth depends on the framebuffer pixelformat. |
V4L2_FBUF_FLAG_GLOBAL_ALPHA |
0x0010 | Use a global alpha value to blend the framebufferwith video images. The blend function is: output = (framebuffer pixel* alpha + video pixel * (255 - alpha)) / 255. The alpha value isdetermined by theglobal_alpha field ofstruct v4l2_window and negotiated with theVIDIOC_S_FMT ioctl, seeSection 4.2andSection 4.4. |
V4L2_FBUF_FLAG_LOCAL_INV_ALPHA |
0x0020 | LikeV4L2_FBUF_FLAG_LOCAL_ALPHA , use the alpha channelof the framebuffer to clip or blend framebuffer pixels with videoimages, but with an inverted alpha value. The blend function is:output = framebuffer pixel * (1 - alpha) + video pixel * alpha. Theactual alpha depth depends on the framebuffer pixel format. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EPERM
-
VIDIOC_S_FBUF
can only be calledby a privileged user to negotiate the parameters for a destructiveoverlay. - EBUSY
-
The framebuffer parameters cannot be changed at thistime because overlay is already enabled, or capturing is enabledand the hardware cannot capture and overlay simultaneously.
- EINVAL
-
The ioctl is not supported or the
VIDIOC_S_FBUF
parameters are unsuitable.
ioctl VIDIOC_G_FMT, VIDIOC_S_FMT,VIDIOC_TRY_FMT
Arguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_G_FMT, VIDIOC_S_FMT, VIDIOC_TRY_FMT
-
argp
-
Description
These ioctls are used to negotiate the format of data(typically image format) exchanged between driver andapplication.
To query the current parameters applications set thetype
field of a structv4l2_format
to the respective buffer (stream)type. For example video capture devices useV4L2_BUF_TYPE_VIDEO_CAPTURE
. When the applicationcalls the VIDIOC_G_FMT
ioctl with a pointer tothis structure the driver fills the respective member of thefmt
union. In case of video capture devicesthat is the struct v4l2_pix_formatpix
member.When the requested buffer type is not supported drivers return anEINVAL error code.
To change the current format parameters applicationsinitialize the type
field and allfields of the respective fmt
union member. For details see the documentation of the various devicestypes inChapter 4. Good practice is to query thecurrent parameters first, and tomodify only those parameters not suitable for the application. Whenthe application calls theVIDIOC_S_FMT
ioctlwith a pointer to av4l2_format
structurethe driver checksand adjusts the parameters against hardware abilities. Driversshould not return an error code unless the input is ambiguous, this isa mechanism to fathom device capabilities and to approach parametersacceptable for both the application and driver. On success the drivermay program the hardware, allocate resources and generally prepare fordata exchange.Finally theVIDIOC_S_FMT
ioctl returns thecurrent format parameters asVIDIOC_G_FMT
does.Very simple, inflexible devices may even ignore all input and alwaysreturn the default parameters. However all V4L2 devices exchangingdata with the application must implement theVIDIOC_G_FMT
andVIDIOC_S_FMT
ioctl. When the requested buffertype is not supported drivers return anEINVAL error code on aVIDIOC_S_FMT
attempt. When I/O is already inprogress or the resource is not available for other reasons driversreturn theEBUSY error code.
The VIDIOC_TRY_FMT
ioctl is equivalentto VIDIOC_S_FMT
with one exception: it does notchange driver state. It can also be called at any time, neverreturningEBUSY. This function is provided tonegotiate parameters, to learn about hardware limitations, withoutdisabling I/O or possibly time consuming hardware preparations.Although strongly recommended drivers are not required to implementthis ioctl.
Table 1. struct v4l2_format
enum v4l2_buf_type | type |
Type of the data stream, see Table 3-2. | |
union | fmt |
||
struct v4l2_pix_format | pix |
Definition of an image format, see Chapter 2, used by video capture and outputdevices. | |
struct v4l2_window | win |
Definition of an overlaid image, see Section 4.2, used by video overlay devices. | |
struct v4l2_vbi_format | vbi |
Raw VBI capture or output parameters. This isdiscussed in more detail in Section 4.7. Used by raw VBIcapture and output devices. | |
struct v4l2_sliced_vbi_format | sliced |
Sliced VBI capture or output parameters. SeeSection 4.8 for details. Used by sliced VBIcapture and output devices. | |
__u8 | raw_data [200] |
Place holder for future extensions and custom(driver defined) formats with type V4L2_BUF_TYPE_PRIVATE and higher. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EBUSY
-
The data format cannot be changed at thistime, for example because I/O is already in progress.
- EINVAL
-
The struct v4l2_format
type
field is invalid, the requested buffer type not supported, orVIDIOC_TRY_FMT
was called and is notsupported with this buffer type.
ioctl VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY
Arguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY
-
argp
-
Description
To get the current tuner or modulator radio frequencyapplications set the tuner
field of astruct v4l2_frequency to the respective tuner or modulator number (onlyinput devices have tuners, only output devices have modulators), zeroout thereserved
array andcall the VIDIOC_G_FREQUENCY
ioctl with a pointerto this structure. The driver stores the current frequency in thefrequency
field.
To change the current tuner or modulator radio frequencyapplications initialize thetuner
,type
andfrequency
fields, and thereserved
array of a struct v4l2_frequency andcall theVIDIOC_S_FREQUENCY
ioctl with a pointerto this structure. When the requested frequency is not possible thedriver assumes the closest possible value. HoweverVIDIOC_S_FREQUENCY
is a write-only ioctl, it doesnot return the actual new frequency.
Table 1. struct v4l2_frequency
__u32 | tuner |
The tuner or modulator index number. This is thesame value as in the struct v4l2_inputtuner field and the struct v4l2_tunerindex field, orthe struct v4l2_outputmodulator field and thestruct v4l2_modulatorindex field. |
enum v4l2_tuner_type | type |
The tuner type. This is the same value as in thestruct v4l2_tunertype field. The field is notapplicable to modulators, i. e. ignored by drivers. |
__u32 | frequency |
Tuning frequency in units of 62.5 kHz, or if thestruct v4l2_tuner or struct v4l2_modulatorcapabilities flagV4L2_TUNER_CAP_LOW is set, in units of 62.5Hz. |
__u32 | reserved [8]; |
Reserved for future extensions. Drivers and applications must set the array to zero. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The
tuner
index is out ofbounds or the value in thetype
field iswrong.
ioctl VIDIOC_G_INPUT, VIDIOC_S_INPUT
Description
To query the current video input applications call theVIDIOC_G_INPUT
ioctl with a pointer to an integerwhere the driver stores the number of the input, as in thestruct v4l2_inputindex
field. This ioctl willfail only when there are no video inputs, returningEINVAL.
To select a video input applications store the number of thedesired input in an integer and call theVIDIOC_S_INPUT
ioctl with a pointer to thisinteger. Side effects are possible. For example inputs may supportdifferent video standards, so the driver may implicitly switch thecurrent standard. It is good practice to select an input beforequerying or negotiating any other parameters.
Information about video inputs is available using theVIDIOC_ENUMINPUT
ioctl.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The number of the video input is out of bounds, orthere are no video inputs at all and this ioctl is notsupported.
- EBUSY
-
I/O is in progress, the input cannot beswitched.
ioctl VIDIOC_G_JPEGCOMP, VIDIOC_S_JPEGCOMP
Description
[to do]
Ronald Bultje elaborates:
APP is some application-specific information. Theapplication can set it itself, and it'll be stored in the JPEG-encodedfields (eg; interlacing information for in an AVI or so). COM is thesame, but it's comments, like 'encoded by me' or so.
jpeg_markers describes whether the huffman tables,quantization tables and the restart interval information (allJPEG-specific stuff) should be stored in the JPEG-encoded fields.These define how the JPEG field is encoded. If you omit them,applications assume you've used standard encoding. You usually do wantto add them.
Table 1. struct v4l2_jpegcompression
int | quality |
|
int | APPn |
|
int | APP_len |
|
char | APP_data [60] |
|
int | COM_len |
|
char | COM_data [60] |
|
__u32 | jpeg_markers |
See Table 2. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
This ioctl is not supported.
ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
Arguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
-
argp
-
Description
To query the attributes of a modulator applications initializethe index
field and zero out thereserved
array of a struct v4l2_modulator andcall theVIDIOC_G_MODULATOR
ioctl with a pointerto this structure. Drivers fill the rest of the structure or return anEINVAL error code when the index is out of bounds. To enumerate all modulatorsapplications shall begin at index zero, incrementing by one until thedriver returns EINVAL.
Modulators have two writable properties, an audiomodulation set and the radio frequency. To change the modulated audiosubprograms, applications initialize theindex
andtxsubchans
fields and thereserved
array and call theVIDIOC_S_MODULATOR
ioctl. Drivers may choose adifferent audio modulation if the request cannot be satisfied. Howeverthis is a write-only ioctl, it does not return the actual audiomodulation selected.
To change the radio frequency the VIDIOC_S_FREQUENCY
ioctlis available.
Table 1. struct v4l2_modulator
__u32 | index |
Identifies the modulator, set by theapplication. |
__u8 | name [32] |
Name of the modulator, a NUL-terminated ASCIIstring. This information is intended for the user. |
__u32 | capability |
Modulator capability flags. No flags are definedfor this field, the tuner flags in struct v4l2_tunerare used accordingly. The audio flags indicate the abilityto encode audio subprograms. They will notchange for example with the current video standard. |
__u32 | rangelow |
The lowest tunable frequency in units of 62.5KHz, or if the capability flagV4L2_TUNER_CAP_LOW is set, in units of 62.5Hz. |
__u32 | rangehigh |
The highest tunable frequency in units of 62.5KHz, or if the capability flagV4L2_TUNER_CAP_LOW is set, in units of 62.5Hz. |
__u32 | txsubchans |
With this field applications can determine howaudio sub-carriers shall be modulated. It contains a set of flags asdefined inTable 2. Note the tunerrxsubchans flags are reused, but thesemantics are different. Video output devices are assumed to have ananalog or PCM audio input with 1-3 channels. Thetxsubchans flags select one or morechannels for modulation, together with some audio subprogramindicator, for example a stereo pilot tone. |
__u32 | reserved [4] |
Reserved for future extensions. Drivers andapplications must set the array to zero. |
Table 2. Modulator Audio Transmission Flags
V4L2_TUNER_SUB_MONO |
0x0001 | Modulate channel 1 as mono audio, when the inputhas more channels, a down-mix of channel 1 and 2. This flag does notcombine withV4L2_TUNER_SUB_STEREO orV4L2_TUNER_SUB_LANG1 . |
V4L2_TUNER_SUB_STEREO |
0x0002 | Modulate channel 1 and 2 as left and rightchannel of a stereo audio signal. When the input has only one channelor two channels andV4L2_TUNER_SUB_SAP is alsoset, channel 1 is encoded as left and right channel. This flag doesnot combine withV4L2_TUNER_SUB_MONO orV4L2_TUNER_SUB_LANG1 . When the driver does notsupport stereo audio it shall fall back to mono. |
V4L2_TUNER_SUB_LANG1 |
0x0008 | Modulate channel 1 and 2 as primary and secondarylanguage of a bilingual audio signal. When the input has only onechannel it is used for both languages. It is not possible to encodethe primary or secondary language only. This flag does not combinewithV4L2_TUNER_SUB_MONO orV4L2_TUNER_SUB_STEREO . If the hardware does notsupport the respective audio matrix, or the current video standarddoes not permit bilingual audio theVIDIOC_S_MODULATOR ioctl shall return anEINVAL error codeand the driver shall fall back to mono or stereo mode. |
V4L2_TUNER_SUB_LANG2 |
0x0004 | Same effect asV4L2_TUNER_SUB_LANG1 . |
V4L2_TUNER_SUB_SAP |
0x0004 | When combined with V4L2_TUNER_SUB_MONO the first channel is encoded as mono audio, the lastchannel as Second Audio Program. When the input has only one channelit is used for both audio tracks. When the input has three channelsthe mono track is a down-mix of channel 1 and 2. When combined withV4L2_TUNER_SUB_STEREO channel 1 and 2 areencoded as left and right stereo audio, channel 3 as Second AudioProgram. When the input has only two channels, the first is encoded asleft and right channel and the second as SAP. When the input has onlyone channel it is used for all audio tracks. It is not possible toencode a Second Audio Program only. This flag must combine withV4L2_TUNER_SUB_MONO orV4L2_TUNER_SUB_STEREO . If the hardware does notsupport the respective audio matrix, or the current video standarddoes not permit SAP theVIDIOC_S_MODULATOR ioctlshall return anEINVAL error code and driver shall fall back to mono or stereomode. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_modulator
index
is out of bounds.
ioctl VIDIOC_G_OUTPUT, VIDIOC_S_OUTPUT
Description
To query the current video output applications call theVIDIOC_G_OUTPUT
ioctl with a pointer to an integerwhere the driver stores the number of the output, as in thestruct v4l2_outputindex
field. This ioctlwill fail only when there are no video outputs, returning theEINVAL error code.
To select a video output applications store the number of thedesired output in an integer and call theVIDIOC_S_OUTPUT
ioctl with a pointer to this integer.Side effects are possible. For example outputs may support differentvideo standards, so the driver may implicitly switch the currentstandard. It is good practice to select an output before querying ornegotiating any other parameters.
Information about video outputs is available using theVIDIOC_ENUMOUTPUT
ioctl.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The number of the video output is out of bounds, orthere are no video outputs at all and this ioctl is notsupported.
- EBUSY
-
I/O is in progress, the output cannot beswitched.
ioctl VIDIOC_G_PARM, VIDIOC_S_PARM
Description
The current video standard determines a nominal number offrames per second. If less than this number of frames is to becaptured or output, applications can request frame skipping orduplicating on the driver side. This is especially useful when usingtheread()
or write()
, whichare not augmented by timestamps or sequence counters, and to avoidunneccessary data copying.
Further these ioctls can be used to determine the number ofbuffers used internally by a driver in read/write mode. Forimplications see the section discussing theread()
function.
To get and set the streaming parameters applications callthe VIDIOC_G_PARM
andVIDIOC_S_PARM
ioctl, respectively. They take apointer to a structv4l2_streamparm
whichcontains a union holding separate parameters for input and outputdevices.
Table 1. struct v4l2_streamparm
enum v4l2_buf_type | type |
The buffer (stream) type, same as struct v4l2_formattype , set by the application. |
|
union | parm |
||
struct v4l2_captureparm | capture |
Parameters for capture devices, used whentype isV4L2_BUF_TYPE_VIDEO_CAPTURE . |
|
struct v4l2_outputparm | output |
Parameters for output devices, used whentype isV4L2_BUF_TYPE_VIDEO_OUTPUT . |
|
__u8 | raw_data [200] |
A place holder for future extensions and custom(driver defined) buffer types V4L2_BUF_TYPE_PRIVATE andhigher. |
Table 2. struct v4l2_captureparm
__u32 | capability |
See Table 4. |
__u32 | capturemode |
Set by drivers and applications, see Table 5. |
struct v4l2_fract | timeperframe |
This is is the desired period betweensuccessive frames captured by the driver, in seconds. Thefield is intended to skip frames on the driver side, saving I/Obandwidth. Applications store here the desired frameperiod, drivers return the actual frame period, which must be greateror equal to the nominal frame period determined by the current videostandard (struct v4l2_standard Drivers support this function only when they set the |
__u32 | extendedmode |
Custom (driver specific) streaming parameters. Whenunused, applications and drivers must set this field to zero.Applications using this field should check the driver name andversion, seeSection 1.2. |
__u32 | readbuffers |
Applications set this field to the desired numberof buffers used internally by the driver inread() mode. Driversreturn the actual number of buffers. When an application requests zerobuffers, drivers should just return the current setting rather thanthe minimum or an error code. For details seeSection 3.1. |
__u32 | reserved [4] |
Reserved for future extensions. Drivers andapplications must set the array to zero. |
Table 3. struct v4l2_outputparm
__u32 | capability |
See Table 4. |
__u32 | outputmode |
Set by drivers and applications, see Table 5. |
struct v4l2_fract | timeperframe |
This is is the desired period betweensuccessive frames output by the driver, in seconds. |
The field is intended torepeat frames on the driver side in Applications store here the desired frameperiod, drivers return the actual frame period, which must be greateror equal to the nominal frame period determined by the current videostandard (struct v4l2_standard Drivers support this function only when they set the |
||
__u32 | extendedmode |
Custom (driver specific) streaming parameters. Whenunused, applications and drivers must set this field to zero.Applications using this field should check the driver name andversion, seeSection 1.2. |
__u32 | writebuffers |
Applications set this field to the desired numberof buffers used internally by the driver inwrite() mode. Drivers return the actual number ofbuffers. When an application requests zero buffers, drivers shouldjust return the current setting rather than the minimum or an errorcode. For details see Section 3.1. |
__u32 | reserved [4] |
Reserved for future extensions. Drivers andapplications must set the array to zero. |
Table 4. Streaming Parameters Capabilites
V4L2_CAP_TIMEPERFRAME |
0x1000 | The frame skipping/repeating controlled by thetimeperframe field is supported. |
Table 5. Capture Parameters Flags
V4L2_MODE_HIGHQUALITY |
0x0001 | High quality imaging mode. High quality modeis intended for still imaging applications. The idea is to get thebest possible image quality that the hardware can deliver. It is notdefined how the driver writer may achieve that; it will depend on thehardware and the ingenuity of the driver writer. High quality mode isa different mode from the the regular motion video capture modes. Inhigh quality mode:
|
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
This ioctl is not supported.
ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY
Name
VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY -- Query or request the access priority associated with afile descriptorArguments
-
fd
-
File descriptor returned by
open()
. -
request
-
VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY
-
argp
-
Pointer to an enum v4l2_priority type.
Description
To query the current access priorityapplications call the VIDIOC_G_PRIORITY
ioctlwith a pointer to an enum v4l2_priority variable where the driver storesthe current priority.
To request an access priority applications store thedesired priority in an enum v4l2_priority variable and callVIDIOC_S_PRIORITY
ioctl with a pointer to thisvariable.
Table 1. enum v4l2_priority
V4L2_PRIORITY_UNSET |
0 | |
V4L2_PRIORITY_BACKGROUND |
1 | Lowest priority, usually applications running inbackground, for example monitoring VBI transmissions. A proxyapplication running in user space will be necessary if multipleapplications want to read from a device at this priority. |
V4L2_PRIORITY_INTERACTIVE |
2 | |
V4L2_PRIORITY_DEFAULT |
2 | Medium priority, usually applications started andinteractively controlled by the user. For example TV viewers, Teletextbrowsers, or just "panel" applications to change the channel or videocontrols. This is the default priority unless an application requestsanother. |
V4L2_PRIORITY_RECORD |
3 | Highest priority. Only one file descriptor can havethis priority, it blocks any other fd from changing device properties.Usually applications which must not be interrupted, like videorecording. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The requested priority value is invalid, or thedriver does not support access priorities.
- EBUSY
-
Another application already requested higherpriority.
ioctl VIDIOC_G_SLICED_VBI_CAP
Description
To find out which data services are supported by a slicedVBI capture or output device, applications initialize thetype
field of a struct v4l2_sliced_vbi_cap,clear the reserved
array andcall the VIDIOC_G_SLICED_VBI_CAP
ioctl. Thedriver fills in the remaining fields or returns anEINVAL error code if thesliced VBI API is unsupported ortype
is invalid.
Note the type
field was added,and the ioctl changed from read-only to write-read, in Linux 2.6.19.
Table 1. struct v4l2_sliced_vbi_cap
__u16 | service_set |
A set of all data servicessupported by the driver. Equal to the union of all elements of theservice_lines array. |
||
__u16 | service_lines [2][24] |
Each element of this arraycontains a set of data services the hardware can look for or insertinto a particular scan line. Data services are defined inTable 2. Array indices map to ITU-Rline numbers (see alsoFigure 4-2 andFigure 4-3) as follows: | ||
Element | 525 line systems | 625 line systems | ||
service_lines [0][1] |
1 | 1 | ||
service_lines [0][23] |
23 | 23 | ||
service_lines [1][1] |
264 | 314 | ||
service_lines [1][23] |
286 | 336 | ||
The number of VBI lines thehardware can capture or output per frame, or the number of services itcan identify on a given line may be limited. For example on PAL line16 the hardware may be able to look for a VPS or Teletext signal, butnot both at the same time. Applications can learn about these limitsusing the VIDIOC_S_FMT ioctl as described in Section 4.8. |
||||
Drivers must setservice_lines [0][0] andservice_lines [1][0] to zero. |
||||
enum v4l2_buf_type | type |
Type of the data stream, see Table 3-2. Should beV4L2_BUF_TYPE_SLICED_VBI_CAPTURE orV4L2_BUF_TYPE_SLICED_VBI_OUTPUT . |
||
__u32 | reserved [3] |
This array is reserved for futureextensions. Applications and drivers must set it to zero. |
Table 2. Sliced VBI services
Symbol | Value | Reference | Lines, usually | Payload |
---|---|---|---|---|
V4L2_SLICED_TELETEXT_B (TeletextSystem B) |
0x0001 | ETS 300 706,ITU BT.653 | PAL/SECAM line 7-22, 320-335 (second field 7-22) | Last 42 of the 45 byte Teletext packet, that iswithout clock run-in and framing code, lsb first transmitted. |
V4L2_SLICED_VPS |
0x0400 | ETS 300 231 | PAL line 16 | Byte number 3 to 15 according to Figure 9 ofETS 300 231, lsb first transmitted. |
V4L2_SLICED_CAPTION_525 |
0x1000 | EIA 608-B | NTSC line 21, 284 (second field 21) | Two bytes in transmission order, including paritybit, lsb first transmitted. |
V4L2_SLICED_WSS_625 |
0x4000 | EN 300 294,ITU BT.1119 | PAL/SECAM line 23 | Byte 0 1 msb lsb msb lsb Bit 7 6 5 4 3 2 1 0 x x 13 12 11 10 9 |
V4L2_SLICED_VBI_525 |
0x1000 | Set of services applicable to 525line systems. | ||
V4L2_SLICED_VBI_625 |
0x4401 | Set of services applicable to 625line systems. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The device does not support sliced VBI capturing oroutput, or the value in the
type
field iswrong.
ioctl VIDIOC_G_STD, VIDIOC_S_STD
Description
To query and select the current video standard applicationsuse the VIDIOC_G_STD
and VIDIOC_S_STD
ioctls which take a pointer to av4l2_std_id type as argument.VIDIOC_G_STD
canreturn a single flag or a set of flags as in struct v4l2_standard fieldid
. The flags must be unambiguous suchthat they appear in only one enumeratedv4l2_standard
structure.
VIDIOC_S_STD
accepts one or moreflags, being a write-only ioctl it does not return the actual new standard asVIDIOC_G_STD
does. When no flags are given orthe current input does not support the requested standard the driverreturns an EINVAL error code. When the standard set is ambiguous drivers mayreturnEINVAL or choose any of the requestedstandards.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
This ioctl is not supported, or the
VIDIOC_S_STD
parameter was unsuitable.
ioctl VIDIOC_G_TUNER, VIDIOC_S_TUNER
Description
To query the attributes of a tuner applications initialize theindex
field and zero out thereserved
array of a struct v4l2_tuner and call theVIDIOC_G_TUNER
ioctl with a pointer to thisstructure. Drivers fill the rest of the structure or return anEINVAL error code when the index is out of bounds. To enumerate all tunersapplications shall begin at index zero, incrementing by one until thedriver returns EINVAL.
Tuners have two writable properties, the audio mode andthe radio frequency. To change the audio mode, applications initializetheindex
,audmode
andreserved
fields and call theVIDIOC_S_TUNER
ioctl. This willnot change the current tuner, which is determinedby the current video input. Drivers may choose a different audio modeif the requested mode is invalid or unsupported. Since this is awrite-only ioctl, it does not return the actuallyselected audio mode.
To change the radio frequency the VIDIOC_S_FREQUENCY
ioctlis available.
Table 1. struct v4l2_tuner
__u32 | index |
Identifies the tuner, set by theapplication. | |
__u8 | name [32] |
Name of the tuner, aNUL-terminated ASCII string. This information is intended for theuser. |
|
enum v4l2_tuner_type | type |
Type of the tuner, see Table 2. | |
__u32 | capability |
Tuner capability flags, seeTable 3. Audio flags indicate the abilityto decode audio subprograms. They willnotchange, for example with the current video standard. Whenthe structure refers to a radio tuner only the |
|
__u32 | rangelow |
The lowest tunable frequency inunits of 62.5 kHz, or if the capability flag V4L2_TUNER_CAP_LOW is set, in units of 62.5Hz. |
|
__u32 | rangehigh |
The highest tunable frequency inunits of 62.5 kHz, or if the capability flag V4L2_TUNER_CAP_LOW is set, in units of 62.5Hz. |
|
__u32 | rxsubchans |
Some tuners or audiodecoders can determine the received audio subprograms by analyzingaudio carriers, pilot tones or other indicators. To pass thisinformation drivers set flags defined inTable 4 in this field. Forexample: |
|
V4L2_TUNER_SUB_MONO |
receiving mono audio | ||
STEREO | SAP |
receiving stereo audio and a secondary audioprogram | ||
MONO | STEREO |
receiving mono or stereo audio, the hardware cannotdistinguish | ||
LANG1 | LANG2 |
receiving bilingual audio | ||
MONO | STEREO | LANG1 | LANG2 |
receiving mono, stereo or bilingualaudio | ||
When the This field is valid only if this is the tuner of thecurrent video input, or when the structure refers to a radiotuner. |
|||
__u32 | audmode |
The selected audio mode, seeTable 5 for valid values. The audio mode doesnot affect audio subprogram detection, and like acontrol it does not automatically changeunless the requested mode is invalid or unsupported. SeeTable 6 for possible results whenthe selected and received audio programs do notmatch. Currently this is the only field of struct |
|
__u32 | signal |
The signal strength if known, rangingfrom 0 to 65535. Higher values indicate a better signal. | |
__s32 | afc |
Automatic frequency control: When theafc value is negative, the frequency is toolow, when positive too high. |
|
__u32 | reserved [4] |
Reserved for future extensions. Drivers andapplications must set the array to zero. |
Table 3. Tuner and Modulator Capability Flags
V4L2_TUNER_CAP_LOW |
0x0001 | When set, tuning frequencies are expressed in units of62.5 Hz, otherwise in units of 62.5 kHz. |
V4L2_TUNER_CAP_NORM |
0x0002 | This is a multi-standard tuner; the video standardcan or must be switched. (B/G PAL tuners for example are typically not considered multi-standard because the video standard is automatically determined from the frequency band.) The set of supported video standards is available from the struct v4l2_input pointing to this tuner, see the description of ioctlVIDIOC_ENUMINPUT for details. OnlyV4L2_TUNER_ANALOG_TV tuners can have this capability. |
V4L2_TUNER_CAP_STEREO |
0x0010 | Stereo audio reception is supported. |
V4L2_TUNER_CAP_LANG1 |
0x0040 | Reception of the primary language of a bilingualaudio program is supported. Bilingual audio is a feature oftwo-channel systems, transmitting the primary language monaural on themain audio carrier and a secondary language monaural on a secondcarrier. OnlyV4L2_TUNER_ANALOG_TV tuners can have this capability. |
V4L2_TUNER_CAP_LANG2 |
0x0020 | Reception of the secondary language of a bilingualaudio program is supported. OnlyV4L2_TUNER_ANALOG_TV tuners can have this capability. |
V4L2_TUNER_CAP_SAP |
0x0020 | Reception of a secondary audio program issupported. This is a feature of the BTSC system which accompanies theNTSC video standard. Two audio carriers are available for mono orstereo transmissions of a primary language, and an independent thirdcarrier for a monaural secondary language. Only Note the |
Table 4. Tuner Audio Reception Flags
V4L2_TUNER_SUB_MONO |
0x0001 | The tuner receives a mono audio signal. |
V4L2_TUNER_SUB_STEREO |
0x0002 | The tuner receives a stereo audio signal. |
V4L2_TUNER_SUB_LANG1 |
0x0008 | The tuner receives the primary language of abilingual audio signal. Drivers must clear this flag when the currentvideo standard isV4L2_STD_NTSC_M . |
V4L2_TUNER_SUB_LANG2 |
0x0004 | The tuner receives the secondary language of abilingual audio signal (or a second audio program). |
V4L2_TUNER_SUB_SAP |
0x0004 | The tuner receives a Second Audio Program. Note theV4L2_TUNER_SUB_LANG2 andV4L2_TUNER_SUB_SAP flags are synonyms. TheV4L2_TUNER_SUB_SAP flag applies when thecurrent video standard is V4L2_STD_NTSC_M . |
Table 5. Tuner Audio Modes
V4L2_TUNER_MODE_MONO |
0 | Play mono audio. When the tuner receives a stereosignal this a down-mix of the left and right channel. When the tunerreceives a bilingual or SAP signal this mode selects the primarylanguage. |
V4L2_TUNER_MODE_STEREO |
1 | Play stereo audio. When the tuner receivesbilingual audio it may play different languages on the left and rightchannel or the primary language on both channels. behave as in monomode. Playing different languages in this mode isdeprecated. New drivers should do this only in When the tunerreceives no stereo signal or does not support stereo reception thedriver shall fall back to |
V4L2_TUNER_MODE_LANG1 |
3 | Play the primary language, mono or stereo. OnlyV4L2_TUNER_ANALOG_TV tuners support thismode. |
V4L2_TUNER_MODE_LANG2 |
2 | Play the secondary language, mono. When the tunerreceives no bilingual audio or SAP, or their reception is notsupported the driver shall fall back to mono or stereo mode. OnlyV4L2_TUNER_ANALOG_TV tuners support thismode. |
V4L2_TUNER_MODE_SAP |
2 | Play the Second Audio Program. When the tunerreceives no bilingual audio or SAP, or their reception is notsupported the driver shall fall back to mono or stereo mode. OnlyV4L2_TUNER_ANALOG_TV tuners support this mode.Note theV4L2_TUNER_MODE_LANG2 andV4L2_TUNER_MODE_SAP are synonyms. |
V4L2_TUNER_MODE_LANG1_LANG2 |
4 | Play the primary language on the left channel, thesecondary language on the right channel. When the tuner receives nobilingual audio or SAP, it shall fall back toMODE_LANG1 orMODE_MONO .OnlyV4L2_TUNER_ANALOG_TV tuners support thismode. |
Table 6. Tuner Audio Matrix
SelectedV4L2_TUNER_MODE_ |
|||||
---|---|---|---|---|---|
Received V4L2_TUNER_SUB_ |
MONO |
STEREO |
LANG1 |
LANG2 = SAP |
LANG1_LANG2 [a] |
MONO |
Mono | Mono/Mono | Mono | Mono | Mono/Mono |
MONO | SAP |
Mono | Mono/Mono | Mono | SAP | Mono/SAP (preferred) or Mono/Mono |
STEREO |
L+R | L/R | Stereo L/R (preferred) or Mono L+R | Stereo L/R (preferred) or Mono L+R | L/R (preferred) or L+R/L+R |
STEREO | SAP |
L+R | L/R | Stereo L/R (preferred) or Mono L+R | SAP | L+R/SAP (preferred) or L/R or L+R/L+R |
LANG1 | LANG2 |
Language 1 | Lang1/Lang2 (deprecated[b]) orLang1/Lang1 | Language 1 | Language 2 | Lang1/Lang2 (preferred) or Lang1/Lang1 |
Notes: a. This mode has been added in Linux 2.6.17 and may not be supported by olderdrivers. b. Playback ofboth languages in MODE_STEREO is deprecated. Inthe future drivers should produce only the primary language in thismode. Applications should requestMODE_LANG1_LANG2 to record both languages or astereo signal. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_tuner
index
isout of bounds.
ioctl VIDIOC_LOG_STATUS
Description
As the video/audio devices become more complicated itbecomes harder to debug problems. When this ioctl is called the driverwill output the current device status to the kernel log. This isparticular useful when dealing with problems like no sound, no videoand incorrectly tuned channels. Also many modern devices autodetectvideo and audio standards and this ioctl will report what the devicethinks what the standard is. Mismatches may give an indication wherethe problem is.
This ioctl is optional and not all drivers support it. Itwas introduced in Linux 2.6.15.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The driver does not support this ioctl.
ioctl VIDIOC_OVERLAY
Description
This ioctl is part of the video overlay I/O method. Applications call VIDIOC_OVERLAY
to start or stop the overlay. It takes a pointer to an integer which must be set to zero by the application to stop overlay, to one to start.
Drivers do not support VIDIOC_STREAMON
orVIDIOC_STREAMOFF
withV4L2_BUF_TYPE_VIDEO_OVERLAY
.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
Video overlay is not supported, or theparameters have not been set up. See Section 4.2 for the necessary steps.
ioctl VIDIOC_QBUF, VIDIOC_DQBUF
Description
Applications call the VIDIOC_QBUF
ioctlto enqueue an empty (capturing) or filled (output) buffer in thedriver's incoming queue. The semantics depend on the selected I/Omethod.
To enqueue a memory mappedbuffer applications set the type
field of astruct v4l2_buffer to the same buffer type as previously struct v4l2_formattype
and struct v4l2_requestbufferstype
, thememory
field toV4L2_MEMORY_MMAP
and theindex
field. Valid index numbers range fromzero to the number of buffers allocated withVIDIOC_REQBUFS
(struct v4l2_requestbufferscount
) minus one. Thecontents of the struct v4l2_buffer
returnedby aVIDIOC_QUERYBUF
ioctl will do as well. When the buffer isintended for output (type
isV4L2_BUF_TYPE_VIDEO_OUTPUT
orV4L2_BUF_TYPE_VBI_OUTPUT
) applications must alsoinitialize thebytesused
,field
andtimestamp
fields. SeeSection 3.5 for details. WhenVIDIOC_QBUF
is called with a pointer to thisstructure the driver sets theV4L2_BUF_FLAG_MAPPED
andV4L2_BUF_FLAG_QUEUED
flags and clears theV4L2_BUF_FLAG_DONE
flag in theflags
field, or it returns anEINVAL error code.
To enqueue a user pointerbuffer applications set the type
field of astruct v4l2_buffer to the same buffer type as previously struct v4l2_formattype
and struct v4l2_requestbufferstype
, thememory
field toV4L2_MEMORY_USERPTR
and them.userptr
field to the address of thebuffer andlength
to its size. When thebuffer is intended for output additional fields must be set as above.WhenVIDIOC_QBUF
is called with a pointer to thisstructure the driver sets theV4L2_BUF_FLAG_QUEUED
flag and clears theV4L2_BUF_FLAG_MAPPED
andV4L2_BUF_FLAG_DONE
flags in theflags
field, or it returns an error code.This ioctl locks the memory pages of the buffer in physical memory,they cannot be swapped out to disk. Buffers remain locked untildequeued, until theVIDIOC_STREAMOFF
orVIDIOC_REQBUFS
ioctl arecalled, or until the device is closed.
Applications call the VIDIOC_DQBUF
ioctl to dequeue a filled (capturing) or displayed (output) bufferfrom the driver's outgoing queue. They just set thetype
andmemory
fields of a struct v4l2_buffer as above, whenVIDIOC_DQBUF
is called with a pointer to this structure the driver fills theremaining fields or returns an error code.
By default VIDIOC_DQBUF
blocks when nobuffer is in the outgoing queue. When theO_NONBLOCK
flag was given to theopen()
function,VIDIOC_DQBUF
returns immediatelywith an EAGAIN error code when no buffer is available.
The v4l2_buffer
structure isspecified in Section 3.5.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EAGAIN
-
Non-blocking I/O has been selected using
O_NONBLOCK
and no buffer was in the outgoingqueue. - EINVAL
-
The buffer
type
is notsupported, or theindex
is out of bounds,or no buffers have been allocated yet, or theuserptr
orlength
are invalid. - ENOMEM
-
Not enough physical or virtual memory was available toenqueue a user pointer buffer.
- EIO
-
VIDIOC_DQBUF
failed due to aninternal error. Can also indicate temporary problems like signalloss. Note the driver might dequeue an (empty) buffer despitereturning an error, or even stop capturing.
ioctl VIDIOC_QUERYBUF
Description
This ioctl is part of the memorymapping I/O method. It can be used to query the status of abuffer at any time after buffers have been allocated with theVIDIOC_REQBUFS
ioctl.
Applications set the type
field of a struct v4l2_buffer to the same buffer type as previouslystruct v4l2_formattype
and struct v4l2_requestbufferstype
, and theindex
field. Valid index numbers range from zeroto the number of buffers allocated withVIDIOC_REQBUFS
(struct v4l2_requestbufferscount
) minus one.After calling VIDIOC_QUERYBUF
with a pointer to this structure drivers return an error code or fill the rest ofthe structure.
In the flags
field theV4L2_BUF_FLAG_MAPPED
,V4L2_BUF_FLAG_QUEUED
andV4L2_BUF_FLAG_DONE
flags will be valid. Thememory
field will be set toV4L2_MEMORY_MMAP
, the m.offset
contains the offset of the buffer from the start of the device memory,thelength
field its size. The driver mayor may not set the remaining fields and flags, they are meaningless inthis context.
The v4l2_buffer
structure is specified in Section 3.5.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The buffer
type
is notsupported, or theindex
is out of bounds.
ioctl VIDIOC_QUERYCAP
Description
All V4L2 devices support theVIDIOC_QUERYCAP
ioctl. It is used to identifykernel devices compatible with this specification and to obtaininformation about driver and hardware capabilities. The ioctl takes apointer to a struct v4l2_capability which is filled by the driver. When thedriver is not compatible with this specification the ioctl returns anEINVAL error code.
Table 1. struct v4l2_capability
__u8 | driver [16] |
Name of the driver, a unique NUL-terminatedASCII string. For example: "bttv". Driver specific applications canuse this information to verify the driver identity. It is also usefulto work around known bugs, or to identify drivers in error reports.The driver version is stored in the Storing strings in fixed sized arrays is badpractice but unavoidable here. Drivers and applications should takeprecautions to never read or write beyond the end of the array and tomake sure the strings are properly NUL-terminated. |
__u8 | card [32] |
Name of the device, a NUL-terminated ASCII string.For example: "Yoyodyne TV/FM". One driver may support different brandsor models of video hardware. This information is intended for users,for example in a menu of available devices. Since multiple TV cards ofthe same brand may be installed which are supported by the samedriver, this name should be combined with the character device filename (e. g./dev/video2) or thebus_info string to avoidambiguities. |
__u8 | bus_info [32] |
Location of the device in the system, aNUL-terminated ASCII string. For example: "PCI Slot 4". Thisinformation is intended for users, to distinguish multipleidentical devices. If no such information is available the field maysimply count the devices controlled by the driver, or contain theempty string (bus_info [0] = 0). |
__u32 | version |
Version number of the driver. Together withthe |
#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c)) __u32 version = KERNEL_VERSION(0, 8, 1); printf ("Version: %u.%u.%u\n", (version >> 16) & 0xFF, (version >> 8) & 0xFF, version & 0xFF); |
||
__u32 | capabilities |
Device capabilities, see Table 2. |
__u32 | reserved [4] |
Reserved for future extensions. Drivers must setthis array to zero. |
Table 2. Device Capabilities Flags
V4L2_CAP_VIDEO_CAPTURE |
0x00000001 | The device supports the Video Capture interface. |
V4L2_CAP_VIDEO_OUTPUT |
0x00000002 | The device supports the Video Output interface. |
V4L2_CAP_VIDEO_OVERLAY |
0x00000004 | The device supports the Video Overlay interface. A video overlay devicetypically stores captured images directly in the video memory of agraphics card, with hardware clipping and scaling. |
V4L2_CAP_VBI_CAPTURE |
0x00000010 | The device supports the RawVBI Capture interface, providing Teletext and Closed Captiondata. |
V4L2_CAP_VBI_OUTPUT |
0x00000020 | The device supports the Raw VBI Output interface. |
V4L2_CAP_SLICED_VBI_CAPTURE |
0x00000040 | The device supports the Sliced VBI Capture interface. |
V4L2_CAP_SLICED_VBI_OUTPUT |
0x00000080 | The device supports the Sliced VBI Output interface. |
V4L2_CAP_RDS_CAPTURE |
0x00000100 | [to be defined] |
V4L2_CAP_VIDEO_OUTPUT_OVERLAY |
0x00000200 | The device supports the VideoOutput Overlay (OSD) interface. Unlike the VideoOverlay interface, this is a secondary function of videooutput devices and overlays an image onto an outgoing video signal.When the driver sets this flag, it must clear theV4L2_CAP_VIDEO_OVERLAY flag and viceversa.[a] |
V4L2_CAP_TUNER |
0x00010000 | The device has some sort of tuner or modulator toreceive or emit RF-modulated video signals. For more information abouttuner and modulator programming seeSection 1.6. |
V4L2_CAP_AUDIO |
0x00020000 | The device has audio inputs or outputs. It may ormay not support audio recording or playback, in PCM or compressedformats. PCM audio support must be implemented as ALSA or OSSinterface. For more information on audio inputs and outputs seeSection 1.5. |
V4L2_CAP_RADIO |
0x00040000 | This is a radio receiver. |
V4L2_CAP_READWRITE |
0x01000000 | The device supports the read() and/or write()I/O methods. |
V4L2_CAP_ASYNCIO |
0x02000000 | The device supports the asynchronous I/O methods. |
V4L2_CAP_STREAMING |
0x04000000 | The device supports the streaming I/O method. |
Notes: a. The struct v4l2_framebuffer lacks anenum v4l2_buf_type field, therefore the type of overlay is implied by thedriver capabilities. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The device is not compatible with thisspecification.
ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU
Description
To query the attributes of a control applications set theid
field of a struct v4l2_queryctrl and call theVIDIOC_QUERYCTRL
ioctl with a pointer to thisstructure. The driver fills the rest of the structure or returns anEINVAL error code when theid
is invalid.
It is possible to enumerate controls by callingVIDIOC_QUERYCTRL
with successiveid
values starting fromV4L2_CID_BASE
up to and exclusiveV4L2_CID_BASE_LASTP1
. Drivers may returnEINVAL if a control in this range is notsupported. Further applications can enumerate private controls, whichare not defined in this specification, by starting atV4L2_CID_PRIVATE_BASE
and incrementingid
until the driver returnsEINVAL.
In both cases, when the driver sets theV4L2_CTRL_FLAG_DISABLED
flag in theflags
field this control is permanentlydisabled and should be ignored by the application.[24]
When the application ORs id
withV4L2_CTRL_FLAG_NEXT_CTRL
the driver returns thenext supported control, orEINVAL if there isnone. Drivers which do not support this flag yet always returnEINVAL.
Additional information is required for menu controls, thename of menu items. To query them applications set theid
andindex
fields of struct v4l2_querymenu and call theVIDIOC_QUERYMENU
ioctl with a pointer to thisstructure. The driver fills the rest of the structure or returns anEINVAL error code when theid
orindex
is invalid. Menu items are enumeratedby callingVIDIOC_QUERYMENU
with successiveindex
values from struct v4l2_queryctrlminimum
(0) tomaximum
, inclusive.
See also the examples in Section 1.8.
Table 1. struct v4l2_queryctrl
__u32 | id |
Identifies the control, set by the application. SeeTable 1-1 for predefined IDs. When the ID is ORedwith V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returnsthe first control with a higher ID. Drivers which do not support thisflag yet always return anEINVAL error code. |
enum v4l2_ctrl_type | type |
Type of control, see Table 3. |
__u8 | name [32] |
Name of the control, a NUL-terminated ASCIIstring. This information is intended for the user. |
__s32 | minimum |
Minimum value, inclusive. This field gives a lowerbound for V4L2_CTRL_TYPE_INTEGER controls. It maynot be valid for any other type of control, includingV4L2_CTRL_TYPE_INTEGER64 controls. Note this is asigned value. |
__s32 | maximum |
Maximum value, inclusive. This field gives an upperbound for V4L2_CTRL_TYPE_INTEGER controls and thehighest valid index for V4L2_CTRL_TYPE_MENU controls. It may not be valid for any other type of control, includingV4L2_CTRL_TYPE_INTEGER64 controls. Note this is asigned value. |
__s32 | step |
This field gives a step size for Generally drivers should not scale hardwarecontrol values. It may be necessary for example when the This field gives the smallest change ofan integer control actually affecting hardware. Often the informationis needed when the user can change controls by keyboard or GUIbuttons, rather than a slider. When for example a hardware registeraccepts values 0-511 and the driver reports 0-65535, step should be128. Note although signed, the step value is supposed tobe always positive. |
__s32 | default_value |
The default value of aV4L2_CTRL_TYPE_INTEGER ,_BOOLEAN or_MENU control.Not valid for other types of controls. Drivers reset controls onlywhen the driver is loaded, not later, in particular not when thefunc-open; is called. |
__u32 | flags |
Control flags, see Table 4. |
__u32 | reserved [2] |
Reserved for future extensions. Drivers must setthe array to zero. |
Table 2. struct v4l2_querymenu
__u32 | id |
Identifies the control, set by the applicationfrom the respective struct v4l2_queryctrlid . |
__u32 | index |
Index of the menu item, starting at zero, set by the application. |
__u8 | name [32] |
Name of the menu item, a NUL-terminated ASCIIstring. This information is intended for the user. |
__u32 | reserved |
Reserved for future extensions. Drivers must setthe array to zero. |
Table 3. enum v4l2_ctrl_type
Type | minimum |
step |
maximum |
Description |
---|---|---|---|---|
V4L2_CTRL_TYPE_INTEGER |
any | any | any | An integer-valued control ranging from minimum tomaximum inclusive. The step value indicates the increment betweenvalues which are actually different on the hardware. |
V4L2_CTRL_TYPE_BOOLEAN |
0 | 1 | 1 | A boolean-valued control. Zero corresponds to"disabled", and one means "enabled". |
V4L2_CTRL_TYPE_MENU |
0 | 1 | N-1 | The control has a menu of N choices. The names ofthe menu items can be enumerated with theVIDIOC_QUERYMENU ioctl. |
V4L2_CTRL_TYPE_BUTTON |
0 | 0 | 0 | A control which performs an action when set.Drivers must ignore the value passed withVIDIOC_S_CTRL and return anEINVAL error code on aVIDIOC_G_CTRL attempt. |
V4L2_CTRL_TYPE_INTEGER64 |
n/a | n/a | n/a | A 64-bit integer valued control. Minimum, maximumand step size cannot be queried. |
V4L2_CTRL_TYPE_CTRL_CLASS |
n/a | n/a | n/a | This is not a control. WhenVIDIOC_QUERYCTRL is called with a control IDequal to a control class code (seeTable 3), theioctl returns the name of the control class and this control type.Older drivers which do not support this feature return anEINVAL error code. |
Table 4. Control Flags
V4L2_CTRL_FLAG_DISABLED |
0x0001 | This control is permanently disabled and should beignored by the application. Any attempt to change the control willresult in anEINVAL error code. |
V4L2_CTRL_FLAG_GRABBED |
0x0002 | This control is temporarily unchangeable, forexample because another application took over control of therespective resource. Such controls may be displayed specially in auser interface. Attempts to change the control may result in anEBUSY error code. |
V4L2_CTRL_FLAG_READ_ONLY |
0x0004 | This control is permanently readable only. Anyattempt to change the control will result in anEINVAL error code. |
V4L2_CTRL_FLAG_UPDATE |
0x0008 | A hint that changing this control may affect thevalue of other controls within the same control class. Applicationsshould update their user interface accordingly. |
V4L2_CTRL_FLAG_INACTIVE |
0x0010 | This control is not applicable to the currentconfiguration and should be displayed accordingly in a user interface.For example the flag may be set on a MPEG audio level 2 bitratecontrol when MPEG audio encoding level 1 was selected with anothercontrol. |
V4L2_CTRL_FLAG_SLIDER |
0x0020 | A hint that this control is best represented as aslider-like element in a user interface. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
The struct v4l2_queryctrl
id
is invalid. The struct v4l2_querymenuid
orindex
is invalid.
ioctl VIDIOC_QUERYSTD
Description
The hardware may be able to detect the current videostandard automatically. To do so, applications callVIDIOC_QUERYSTD
with a pointer to av4l2_std_id type. Thedriver stores here a set of candidates, this can be a single flag or aset of supported standards if for example the hardware can onlydistinguish between 50 and 60 Hz systems. When detection is notpossible or fails, the set must contain all standards supported by thecurrent video input or output.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
This ioctl is not supported.
ioctl VIDIOC_REQBUFS
Description
This ioctl is used to initiate memorymapped or user pointerI/O. Memory mapped buffers are located in device memory and must beallocated with this ioctl before they can be mapped into theapplication's address space. User buffers are allocated byapplications themselves, and this ioctl is merely used to switch thedriver into user pointer I/O mode.
To allocate device buffers applications initialize threefields of a v4l2_requestbuffers
structure.They set the type
field to the respectivestream or buffer type, thecount
field tothe desired number of buffers, andmemory
must be set to V4L2_MEMORY_MMAP
. When the ioctlis called with a pointer to this structure the driver attempts toallocate the requested number of buffers and stores the actual numberallocated in thecount
field. It can besmaller than the number requested, even zero, when the driver runs outof free memory. A larger number is possible when the driver requiresmore buffers to function correctly.[25] When memory mapping I/O is not supported the ioctlreturns an EINVAL error code.
Applications can call VIDIOC_REQBUFS
again to change the number of buffers, however this cannot succeedwhen any buffers are still mapped. Acount
value of zero frees all buffers, after aborting or finishing any DMAin progress, an implicitVIDIOC_STREAMOFF
.
To negotiate user pointer I/O, applications initialize onlythe type
field and setmemory
toV4L2_MEMORY_USERPTR
. When the ioctl is calledwith a pointer to this structure the driver prepares for user pointerI/O, when this I/O method is not supported the ioctl returns anEINVAL error code.
Table 1. struct v4l2_requestbuffers
__u32 | count |
The number of buffers requested or granted. Thisfield is only used when memory is set toV4L2_MEMORY_MMAP . |
enum v4l2_buf_type | type |
Type of the stream or buffers, this is the sameas the struct v4l2_formattype field. SeeTable 3-2 for valid values. |
enum v4l2_memory | memory |
Applications set this field toV4L2_MEMORY_MMAP orV4L2_MEMORY_USERPTR . |
__u32 | reserved [2] |
A place holder for future extensions and custom(driver defined) buffer types V4L2_BUF_TYPE_PRIVATE andhigher. |
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EBUSY
-
The driver supports multiple opens and I/O is alreadyin progress, or reallocation of buffers was attempted although one ormore are still mapped.
- EINVAL
-
The buffer type (
type
field) or therequested I/O method (memory
) is notsupported.
ioctl VIDIOC_STREAMON, VIDIOC_STREAMOFF
Description
The VIDIOC_STREAMON
andVIDIOC_STREAMOFF
ioctl start and stop the captureor output process during streaming (memorymapping oruser pointer) I/O.
Specifically the capture hardware is disabled and no inputbuffers are filled (if there are any empty buffers in the incomingqueue) untilVIDIOC_STREAMON
has been called.Accordingly the output hardware is disabled, no video signal isproduced untilVIDIOC_STREAMON
has been called.The ioctl will succeed only when at least one output buffer is in theincoming queue.
The VIDIOC_STREAMOFF
ioctl, apart ofaborting or finishing any DMA in progress, unlocks any user pointerbuffers locked in physical memory, and it removes all buffers from theincoming and outgoing queues. That means all images captured but notdequeued yet will be lost, likewise all images enqueued for output butnot transmitted yet. I/O returns to the same state as after callingVIDIOC_REQBUFS
and can be restarted accordingly.
Both ioctls take a pointer to an integer, the desired buffer orstream type. This is the same as struct v4l2_requestbufferstype
.
Note applications can be preempted for unknown periods rightbefore or after theVIDIOC_STREAMON
orVIDIOC_STREAMOFF
calls, there is no notion ofstarting or stopping "now". Buffer timestamps can be used tosynchronize with other events.
Return Value
On success 0 is returned, on error -1 and the errno
variable is set appropriately:
- EINVAL
-
Streaming I/O is not supported, the buffer
type
is not supported, or no buffers havebeen allocated (memory mapping) or enqueued (output) yet.
V4L2 mmap()
Arguments
-
start
-
Map the buffer to this address in the application's address space. When the
MAP_FIXED
flag is specified,start
must be a multiple of thepagesize and mmap will fail when the specified addresscannot be used. Use of this option is discouraged; applications shouldjust specify aNULL
pointer here. -
length
-
Length of the memory area to map. This must be thesame value as returned by the driver in the struct v4l2_buffer
length
field. -
prot
-
The
prot
argument describes thedesired memory protection. Regardless of the device type and thedirection of data exchange it should be set toPROT_READ
|PROT_WRITE
,permitting read and write access to image buffers. Drivers shouldsupport at least this combination of flags. Note the Linuxvideo-buf kernel module, which is used by thebttv, saa7134, saa7146, cx88 and vivi driver supports onlyPROT_READ
|PROT_WRITE
. Whenthe driver does not support the desired protection themmap()
function fails.Note device memory accesses (e. g. the memory on agraphics card with video capturing hardware) may incur a performancepenalty compared to main memory accesses, or reads may besignificantly slower than writes or vice versa. Other I/O methods maybe more efficient in this case.
-
flags
-
The
flags
parameterspecifies the type of the mapped object, mapping options and whethermodifications made to the mapped copy of the page are private to theprocess or are to be shared with other references.MAP_FIXED
requests that thedriver selects no other address than the one specified. If thespecified address cannot be used,mmap()
will fail. IfMAP_FIXED
is specified,start
must be a multiple of the pagesize. Useof this option is discouraged.One of the
MAP_SHARED
orMAP_PRIVATE
flags must be set.MAP_SHARED
allows applications to share themapped memory with other (e. g. child-) processes. Note the Linuxvideo-buf module which is used by the bttv,saa7134, saa7146, cx88 and vivi driver supports onlyMAP_SHARED
.MAP_PRIVATE
requests copy-on-write semantics. V4L2 applications should not set theMAP_PRIVATE
,MAP_DENYWRITE
,MAP_EXECUTABLE
orMAP_ANON
flag. -
fd
-
File descriptor returned by
open()
. -
offset
-
Offset of the buffer in device memory. This must be thesame value as returned by the driver in the struct v4l2_buffer
m
unionoffset
field.
Description
The mmap()
function asks to maplength
bytes starting atoffset
in the memory of the device specified byfd
into the application address space,preferably at address start
. This latteraddress is a hint only, and is usually specified as 0.
Suitable length and offset parameters are queried with theVIDIOC_QUERYBUF
ioctl. Buffers must be allocated with theVIDIOC_REQBUFS
ioctl before they can be queried.
To unmap buffers the munmap()
function is used.
Return Value
On success mmap()
returns a pointer tothe mapped buffer. On errorMAP_FAILED
(-1) isreturned, and theerrno
variable is setappropriately. Possible error codes are:
- EBADF
-
fd
is not a valid filedescriptor. - EACCES
-
fd
isnot open for reading and writing. - EINVAL
-
The
start
orlength
oroffset
are notsuitable. (E. g. they are too large, or not aligned on aPAGESIZE
boundary.)The
flags
orprot
value is not supported.No buffers have been allocated with the
VIDIOC_REQBUFS
ioctl. - ENOMEM
-
Not enough physical or virtual memory was available tocomplete the request.
V4L2 munmap()
Arguments
-
start
-
Address of the mapped buffer as returned by the
mmap()
function. -
length
-
Length of the mapped buffer. This must be the samevalue as given to
mmap()
and returned by thedriver in the struct v4l2_bufferlength
field.
Return Value
On success munmap()
returns 0, onfailure -1 and theerrno
variable is setappropriately:
- EINVAL
-
The
start
orlength
is incorrect, or no buffers have beenmapped yet.
V4L2 open()
Arguments
-
device_name
-
Device to be opened.
-
flags
-
Open flags. Access mode must be
O_RDWR
. This is just a technicality, input devicesstill support only reading and output devices only writing.When the
O_NONBLOCK
flag isgiven, the read() function and theVIDIOC_DQBUF
ioctl will returntheEAGAIN error code when no data is available or no buffer is in the driveroutgoing queue, otherwise these functions block until data becomesavailable. All V4L2 drivers exchanging data with applications mustsupport theO_NONBLOCK
flag.Other flags have no effect.
Description
To open a V4L2 device applications callopen()
with the desired device name. Thisfunction has no side effects; all data format parameters, currentinput or output, control values or other properties remain unchanged.At the firstopen()
call after loading the driverthey will be reset to default values, drivers are never in anundefined state.
Return Value
On success open
returns the new filedescriptor. On error -1 is returned, and theerrno
variable is set appropriately. Possible error codes are:
- EACCES
-
The caller has no permission to access thedevice.
- EBUSY
-
The driver does not support multiple opens and thedevice is already in use.
- ENXIO
-
No device corresponding to this device special fileexists.
- ENOMEM
-
Not enough kernel memory was available to complete therequest.
- EMFILE
-
The process already has the maximum number offiles open.
- ENFILE
-
The limit on the total number of files open on thesystem has been reached.
V4L2 poll()
Description
With the poll()
function applicationscan suspend execution until the driver has captured data or is readyto accept data for output.
When streaming I/O has been negotiated this function waitsuntil a buffer has been filled or displayed and can be dequeued withtheVIDIOC_DQBUF
ioctl. When buffers are already in the outgoingqueue of the driver the function returns immediately.
On success poll()
returns the number offile descriptors that have been selected (that is, file descriptorsfor which therevents
field of therespectivepollfd
structure is non-zero).Capture devices set thePOLLIN
andPOLLRDNORM
flags in therevents
field, output devices thePOLLOUT
andPOLLWRNORM
flags. When the function timed out it returns a value of zero, onfailure it returns-1 and theerrno
variable is set appropriately. When theapplication did not callVIDIOC_QBUF
orVIDIOC_STREAMON
yet thepoll()
function succeeds, but sets thePOLLERR
flag in therevents
field.
When use of the read()
function hasbeen negotiated and the driver does not capture yet, thepoll
function starts capturing. When that failsit returns aPOLLERR
as above. Otherwise it waitsuntil data has been captured and can be read. When the driver capturescontinuously (as opposed to, for example, still images) the functionmay return immediately.
When use of the write()
function hasbeen negotiated thepoll
function just waitsuntil the driver is ready for a non-blockingwrite()
call.
All drivers implementing the read()
orwrite()
function or streaming I/O must alsosupport thepoll()
function.
For more details see thepoll()
manual page.
Return Value
On success, poll()
returns the numberstructures which have non-zerorevents
fields, or zero if the call timed out. On error-1 is returned, and theerrno
variable is set appropriately:
- EBADF
-
One or more of the
ufds
membersspecify an invalid file descriptor. - EBUSY
-
The driver does not support multiple read or writestreams and the device is already in use.
- EFAULT
-
ufds
references an inaccessiblememory area. - EINTR
-
The call was interrupted by a signal.
- EINVAL
-
The
nfds
argument is greaterthanOPEN_MAX
.
V4L2 read()
Description
read()
attempts to read up tocount
bytes from file descriptorfd
into the buffer starting atbuf
. The layout of the data in the buffer isdiscussed in the respective device interface section, see ##. If count
is zero,read()
returns zero and has no other results. Ifcount
is greater thanSSIZE_MAX
, the result is unspecified. Regardlessof thecount
value eachread()
call will provide at most one frame (twofields) worth of data.
By default read()
blocks until databecomes available. When theO_NONBLOCK
flag wasgiven to theopen()
function itreturns immediately with anEAGAIN error code when no data is available. Theselect()
orpoll()
functionscan always be used to suspend execution until data becomes available. Alldrivers supporting theread()
function must alsosupportselect()
andpoll()
.
Drivers can implement read functionality in differentways, using a single or multiple buffers and discarding the oldest ornewest frames once the internal buffers are filled.
read()
never returns a "snapshot" of abuffer being filled. Using a single buffer the driver will stopcapturing when the application starts reading the buffer until theread is finished. Thus only the period of the vertical blankinginterval is available for reading, or the capture rate must fall belowthe nominal frame rate of the video standard.
The behavior ofread()
when called during the active pictureperiod or the vertical blanking separating the top and bottom fielddepends on the discarding policy. A driver discarding the oldestframes keeps capturing into an internal buffer, continuouslyoverwriting the previously, not read frame, and returns the framebeing received at the time of theread()
call assoon as it is complete.
A driver discarding the newest frames stops capturing untilthe next read()
call. The frame being received atread()
time is discarded, returning the followingframe instead. Again this implies a reduction of the capture rate toone half or less of the nominal frame rate. An example of this modelis the video read mode of the bttv driver, initiating a DMA to usermemory whenread()
is called and returning whenthe DMA finished.
In the multiple buffer model drivers maintain a ring ofinternal buffers, automatically advancing to the next free buffer.This allows continuous capturing when the application can empty thebuffers fast enough. Again, the behavior when the driver runs out offree buffers depends on the discarding policy.
Applications can get and set the number of buffers usedinternally by the driver with theVIDIOC_G_PARM
andVIDIOC_S_PARM
ioctls. They are optional, however. The discarding policy is notreported and cannot be changed. For minimum requirements seeChapter 4.
Return Value
On success, the number of bytes read is returned. It is notan error if this number is smaller than the number of bytes requested,or the amount of data required for one frame. This may happen forexample becauseread()
was interrupted by asignal. On error, -1 is returned, and theerrno
variable is set appropriately. In this case the next read will startat the beginning of a new frame. Possible error codes are:
- EAGAIN
-
Non-blocking I/O has been selected usingO_NONBLOCK and no data was immediately available for reading.
- EBADF
-
fd
is not a valid filedescriptor or is not open for reading, or the process already has themaximum number of files open. - EBUSY
-
The driver does not support multiple read streams and thedevice is already in use.
- EFAULT
-
buf
references an inaccessiblememory area. - EINTR
-
The call was interrupted by a signal before anydata was read.
- EIO
-
I/O error. This indicates some hardware problem or afailure to communicate with a remote device (USB camera etc.).
- EINVAL
-
The
read()
function is notsupported by this driver, not on this device, or generally not on thistype of device.
V4L2 select()
Description
With the select()
function applicationscan suspend execution until the driver has captured data or is readyto accept data for output.
When streaming I/O has been negotiated this function waitsuntil a buffer has been filled or displayed and can be dequeued withtheVIDIOC_DQBUF
ioctl. When buffers are already in the outgoingqueue of the driver the function returns immediately.
On success select()
returns the totalnumber of bits set in thefd_set
s. When thefunction timed out it returns a value of zero. On failure it returns-1 and theerrno
variable is set appropriately. When the application did not callVIDIOC_QBUF
orVIDIOC_STREAMON
yet theselect()
function succeeds, setting the bit ofthe file descriptor inreadfds
orwritefds
, but subsequentVIDIOC_DQBUF
callswill fail.[26]
When use of the read()
function hasbeen negotiated and the driver does not capture yet, theselect()
function starts capturing. When thatfails,select()
returns successful and asubsequent read()
call, which also attempts tostart capturing, will return an appropriate error code. When thedriver captures continuously (as opposed to, for example, stillimages) and data is already available theselect()
function returns immediately.
When use of the write()
function hasbeen negotiated theselect()
function just waitsuntil the driver is ready for a non-blockingwrite()
call.
All drivers implementing the read()
orwrite()
function or streaming I/O must alsosupport theselect()
function.
For more details see the select()
manual page.
Return Value
On success, select()
returns the numberof descriptors contained in the three returned descriptor sets, whichwill be zero if the timeout expired. On error-1 is returned, and theerrno
variable is set appropriately; the sets andtimeout
are undefined. Possible error codesare:
- EBADF
-
One or more of the file descriptor sets specified afile descriptor that is not open.
- EBUSY
-
The driver does not support multiple read or writestreams and the device is already in use.
- EFAULT
-
The
readfds
,writefds
,exceptfds
ortimeout
pointer references an inaccessible memoryarea. - EINTR
-
The call was interrupted by a signal.
- EINVAL
-
The
nfds
argument is less thanzero or greater thanFD_SETSIZE
.
V4L2 write()
Description
write()
writes up tocount
bytes to the device referenced by thefile descriptorfd
from the buffer starting atbuf
. When the hardware outputs are not activeyet, this function enables them. Whencount
iszero,write()
returns0 without any other effect.
When the application does not provide more data in time, theprevious video frame, raw VBI image, sliced VPS or WSS data isdisplayed again. Sliced Teletext or Closed Caption data is notrepeated, the driver inserts a blank line instead.
Return Value
On success, the number of bytes written are returned. Zeroindicates nothing was written. On error,-1is returned, and theerrno
variable is setappropriately. In this case the next write will start at the beginningof a new frame. Possible error codes are:
- EAGAIN
-
Non-blocking I/O has been selected using the
O_NONBLOCK
flag and nobuffer space was available to write the data immediately. - EBADF
-
fd
is not a valid filedescriptor or is not open for writing. - EBUSY
-
The driver does not support multiple write streams and thedevice is already in use.
- EFAULT
-
buf
references an inaccessiblememory area. - EINTR
-
The call was interrupted by a signal before anydata was written.
- EIO
-
I/O error. This indicates some hardware problem.
- EINVAL
-
The
write()
function is notsupported by this driver, not on this device, or generally not on thistype of device.
Chapter 6. Changes
The following chapters document the evolution of the V4L2 API,errata or extensions. They are also intended to help application anddriver writers to port or update their code.
6.1. Differences between V4L and V4L2
The Video For Linux API was first introduced in Linux 2.1 tounify and replace various TV and radio device related interfaces,developed independently by driver writers in prior years. Startingwith Linux 2.5 the much improved V4L2 API replaces the V4L API,although existing drivers will continue to support V4L applications inthe future, either directly or through the V4L2 compatibility layer inthevideodev kernel module translating ioctls onthe fly. For a transition period not all drivers will support the V4L2API.
6.1.1. Opening and Closing Devices
For compatibility reasons the character device file namesrecommended for V4L2 video capture, overlay, radio, teletext and rawvbi capture devices did not change from those used by V4L. They arelisted inChapter 4 and below inTable 6-1.
The V4L videodev module automaticallyassigns minor numbers to drivers in load order, depending on theregistered device type. We recommend that V4L2 drivers by defaultregister devices with the same numbers, but the system administratorcan assign arbitrary minor numbers using driver module options. Themajor device number remains 81.
Table 6-1. V4L Device Types, Names and Numbers
V4L prohibits (or used to prohibit) multiple opens of adevice file. V4L2 driversmay support multipleopens, seeSection 1.1 for details and consequences.
V4L drivers respond to V4L2 ioctls with an EINVAL error code. Thecompatibility layer in the V4L2videodev modulecan translate V4L ioctl requests to their V4L2 counterpart, however aV4L2 driver usually needs more preparation to become fully V4Lcompatible. This is covered in more detail inChapter 5.
6.1.2. Querying Capabilities
The V4L VIDIOCGCAP
ioctl isequivalent to V4L2's VIDIOC_QUERYCAP
.
The name
field in structvideo_capability
becamecard
in struct v4l2_capability,type
was replaced bycapabilities
. Note V4L2 does notdistinguish between device types like this, better think of basicvideo input, video output and radio devices supporting a set ofrelated functions like video capturing, video overlay and VBIcapturing. See Section 1.1 for anintroduction.
structvideo_capability type |
struct v4l2_capabilitycapabilities flags |
Purpose |
---|---|---|
VID_TYPE_CAPTURE |
V4L2_CAP_VIDEO_CAPTURE |
The videocapture interface is supported. |
VID_TYPE_TUNER |
V4L2_CAP_TUNER |
The device has a tuner ormodulator. |
VID_TYPE_TELETEXT |
V4L2_CAP_VBI_CAPTURE |
The raw VBIcapture interface is supported. |
VID_TYPE_OVERLAY |
V4L2_CAP_VIDEO_OVERLAY |
The videooverlay interface is supported. |
VID_TYPE_CHROMAKEY |
V4L2_FBUF_CAP_CHROMAKEY infield capability ofstruct v4l2_framebuffer |
Whether chromakey overlay is supported. Formore information on overlay seeSection 4.2. |
VID_TYPE_CLIPPING |
V4L2_FBUF_CAP_LIST_CLIPPING and V4L2_FBUF_CAP_BITMAP_CLIPPING in fieldcapability of struct v4l2_framebuffer |
Whether clipping the overlaid image issupported, see Section 4.2. |
VID_TYPE_FRAMERAM |
V4L2_FBUF_CAP_EXTERNOVERLAY not set in fieldcapability of struct v4l2_framebuffer |
Whether overlay overwrites frame buffer memory,see Section 4.2. |
VID_TYPE_SCALES |
- |
This flag indicates if the hardware can scaleimages. The V4L2 API implies the scale factor by setting the croppingdimensions and image size with theVIDIOC_S_CROP andVIDIOC_S_FMT ioctl, respectively. The driver returns the closest sizes possible.For more information on cropping and scaling seeSection 1.11. |
VID_TYPE_MONOCHROME |
- |
Applications can enumerate the supported imageformats with the VIDIOC_ENUM_FMT ioctl to determine if the devicesupports grey scale capturing only. For more information on imageformats seeChapter 2. |
VID_TYPE_SUBCAPTURE |
- |
Applications can call the VIDIOC_G_CROP ioctlto determine if the device supports capturing a subsection of the fullpicture ("cropping" in V4L2). If not, the ioctl returns theEINVAL error code.For more information on cropping and scaling seeSection 1.11. |
VID_TYPE_MPEG_DECODER |
- |
Applications can enumerate the supported imageformats with the VIDIOC_ENUM_FMT ioctl to determine if the devicesupports MPEG streams. |
VID_TYPE_MPEG_ENCODER |
- |
See above. |
VID_TYPE_MJPEG_DECODER |
- |
See above. |
VID_TYPE_MJPEG_ENCODER |
- |
See above. |
The audios
field was replacedby capabilities
flagV4L2_CAP_AUDIO
, indicatingif the device has any audio inputs or outputs. Todetermine their number applications can enumerate audio inputs withtheVIDIOC_G_AUDIO
ioctl. The audio ioctls are described inSection 1.5.
The maxwidth
,maxheight
,minwidth
andminheight
fields were removed. Calling theVIDIOC_S_FMT
or VIDIOC_TRY_FMT
ioctl with the desired dimensionsreturns the closest size possible, taking into account the currentvideo standard, cropping and scaling limitations.
6.1.3. Video Sources
V4L provides the VIDIOCGCHAN
andVIDIOCSCHAN
ioctl using structvideo_channel
to enumeratethe video inputs of a V4L device. The equivalent V4L2 ioctlsareVIDIOC_ENUMINPUT
,VIDIOC_G_INPUT
andVIDIOC_S_INPUT
using struct v4l2_input as discussed inSection 1.4.
The channel
field countinginputs was renamed toindex
, the videoinput types were renamed as follows:
struct video_channel type |
struct v4l2_inputtype |
---|---|
VIDEO_TYPE_TV |
V4L2_INPUT_TYPE_TUNER |
VIDEO_TYPE_CAMERA |
V4L2_INPUT_TYPE_CAMERA |
Unlike the tuners
fieldexpressing the number of tuners of this input, V4L2 assumes each videoinput is connected to at most one tuner. However a tuner can have morethan one input, i. e. RF connectors, and a device can have multipletuners. The index number of the tuner associated with the input, ifany, is stored in fieldtuner
ofstruct v4l2_input. Enumeration of tuners is discussed inSection 1.6.
The redundant VIDEO_VC_TUNER
flag wasdropped. Video inputs associated with a tuner are of typeV4L2_INPUT_TYPE_TUNER
. TheVIDEO_VC_AUDIO
flag was replaced by theaudioset
field. V4L2 considers devices withup to 32 audio inputs. Each set bit in theaudioset
field represents one audio inputthis video input combines with. For information about audio inputs andhow to switch between them seeSection 1.5.
The norm
field describing thesupported video standards was replaced bystd
. The V4L specification mentions a flagVIDEO_VC_NORM
indicating whether the standard canbe changed. This flag was a later addition together with thenorm
field and has been removed in themeantime. V4L2 has a similar, albeit more comprehensive approachto video standards, seeSection 1.7 for moreinformation.
6.1.4. Tuning
The V4L VIDIOCGTUNER
andVIDIOCSTUNER
ioctl and structvideo_tuner
can be used to enumerate thetuners of a V4L TV or radio device. The equivalent V4L2 ioctls areVIDIOC_G_TUNER
and VIDIOC_S_TUNER
using struct v4l2_tuner. Tuners arecovered inSection 1.6.
The tuner
field counting tunerswas renamed toindex
. The fieldsname
,rangelow
andrangehigh
remained unchanged.
The VIDEO_TUNER_PAL
,VIDEO_TUNER_NTSC
andVIDEO_TUNER_SECAM
flags indicating the supportedvideo standards were dropped. This information is now contained in theassociated struct v4l2_input. No replacement exists for theVIDEO_TUNER_NORM
flag indicating whether thevideo standard can be switched. Themode
field to select a different video standard was replaced by a whole newset of ioctls and structures described inSection 1.7.Due to its ubiquity it should be mentioned the BTTV driver supportsseveral standards in addition to the regularVIDEO_MODE_PAL
(0),VIDEO_MODE_NTSC
,VIDEO_MODE_SECAM
andVIDEO_MODE_AUTO
(3). Namely N/PAL Argentina,M/PAL, N/PAL, and NTSC Japan with numbers 3-6 (sic).
The VIDEO_TUNER_STEREO_ON
flagindicating stereo reception becameV4L2_TUNER_SUB_STEREO
in fieldrxsubchans
. This field also permits thedetection of monaural and bilingual audio, see the definition ofstruct v4l2_tuner for details. Presently no replacement exists for theVIDEO_TUNER_RDS_ON
andVIDEO_TUNER_MBS_ON
flags.
The VIDEO_TUNER_LOW
flag was renamedto V4L2_TUNER_CAP_LOW
in the struct v4l2_tunercapability
field.
The VIDIOCGFREQ
andVIDIOCSFREQ
ioctl to change the tuner frequencywhere renamed toVIDIOC_G_FREQUENCY
andVIDIOC_S_FREQUENCY
. Theytake a pointer to a struct v4l2_frequency instead of an unsigned longinteger.
6.1.5. Image Properties
V4L2 has no equivalent of theVIDIOCGPICT
and VIDIOCSPICT
ioctl and struct video_picture
. The followingfields where replaced by V4L2 controls accessible with theVIDIOC_QUERYCTRL
,VIDIOC_G_CTRL
andVIDIOC_S_CTRL
ioctls:
struct video_picture |
V4L2 Control ID |
---|---|
brightness |
V4L2_CID_BRIGHTNESS |
hue |
V4L2_CID_HUE |
colour |
V4L2_CID_SATURATION |
contrast |
V4L2_CID_CONTRAST |
whiteness |
V4L2_CID_WHITENESS |
The V4L picture controls are assumed to range from 0 to65535 with no particular reset value. The V4L2 API permits arbitrarylimits and defaults which can be queried with theVIDIOC_QUERYCTRL
ioctl. For general information about controls seeSection 1.8.
The depth
(average number ofbits per pixel) of a video image is implied by the selected imageformat. V4L2 does not explicitely provide such information assumingapplications recognizing the format are aware of the image depth andothers need not know. The palette
fieldmoved into the struct v4l2_pix_format:
struct video_picture palette |
struct v4l2_pix_formatpixfmt |
---|---|
VIDEO_PALETTE_GREY |
|
VIDEO_PALETTE_HI240 |
|
VIDEO_PALETTE_RGB565 |
|
VIDEO_PALETTE_RGB555 |
|
VIDEO_PALETTE_RGB24 |
|
VIDEO_PALETTE_RGB32 |
|
VIDEO_PALETTE_YUV422 |
|
|
|
VIDEO_PALETTE_UYVY |
|
VIDEO_PALETTE_YUV420 |
None |
VIDEO_PALETTE_YUV411 |
|
VIDEO_PALETTE_RAW |
Nonee |
VIDEO_PALETTE_YUV422P |
|
VIDEO_PALETTE_YUV411P |
|
VIDEO_PALETTE_YUV420P |
|
VIDEO_PALETTE_YUV410P |
|
Notes: a. This is a custom format used by the BTTVdriver, not one of the V4L2 standard formats. b. Presumably all V4L RGB formats arelittle-endian, although some drivers might interpret them according to machine endianess. V4L2 defines little-endian, big-endian and red/blueswapped variants. For details seeSection 2.4. c. VIDEO_PALETTE_YUV422 andVIDEO_PALETTE_YUYV are the same formats. SomeV4L drivers respond to one, some to the other.d. Not to be confused with V4L2_PIX_FMT_YUV411P , which is a planarformat.e. V4L explains thisas: "RAW capture (BT848)" f. Not to be confused with V4L2_PIX_FMT_Y41P , which is a packedformat. |
V4L2 image formats are defined in Chapter 2. The image format can be selected with theVIDIOC_S_FMT
ioctl.
6.1.6. Audio
The VIDIOCGAUDIO
andVIDIOCSAUDIO
ioctl and structvideo_audio
are used to enumerate theaudio inputs of a V4L device. The equivalent V4L2 ioctls areVIDIOC_G_AUDIO
and VIDIOC_S_AUDIO
using struct v4l2_audio asdiscussed inSection 1.5.
The audio
"channel number"field counting audio inputs was renamed toindex
.
On VIDIOCSAUDIO
themode
field selectsoneof theVIDEO_SOUND_MONO
,VIDEO_SOUND_STEREO
,VIDEO_SOUND_LANG1
orVIDEO_SOUND_LANG2
audio demodulation modes. Whenthe current audio standard is BTSCVIDEO_SOUND_LANG2
refers to SAP andVIDEO_SOUND_LANG1
is meaningless. Alsoundocumented in the V4L specification, there is no way to query theselected mode. OnVIDIOCGAUDIO
the driver returnstheactually received audio programmes in thisfield. In the V4L2 API this information is stored in the struct v4l2_tunerrxsubchans
andaudmode
fields, respectively. SeeSection 1.6 for more information on tuners. Related to audiomodes struct v4l2_audio also reports if this is a mono or stereoinput, regardless if the source is a tuner.
The following fields where replaced by V4L2 controlsaccessible with the VIDIOC_QUERYCTRL
, VIDIOC_G_CTRL
andVIDIOC_S_CTRL
ioctls:
structvideo_audio |
V4L2 Control ID |
---|---|
volume |
V4L2_CID_AUDIO_VOLUME |
bass |
V4L2_CID_AUDIO_BASS |
treble |
V4L2_CID_AUDIO_TREBLE |
balance |
V4L2_CID_AUDIO_BALANCE |
To determine which of these controls are supported by adriver V4L provides theflags
VIDEO_AUDIO_VOLUME
,VIDEO_AUDIO_BASS
,VIDEO_AUDIO_TREBLE
andVIDEO_AUDIO_BALANCE
. In the V4L2 API theVIDIOC_QUERYCTRL
ioctl reports if the respective control issupported. Accordingly the VIDEO_AUDIO_MUTABLE
and VIDEO_AUDIO_MUTE
flags where replaced by thebooleanV4L2_CID_AUDIO_MUTE
control.
All V4L2 controls have a step
attribute replacing the structvideo_audio
step
field. The V4L audio controls areassumed to range from 0 to 65535 with no particular reset value. TheV4L2 API permits arbitrary limits and defaults which can be queriedwith theVIDIOC_QUERYCTRL
ioctl. For general information aboutcontrols seeSection 1.8.
6.1.7. Frame Buffer Overlay
The V4L2 ioctls equivalent toVIDIOCGFBUF
and VIDIOCSFBUF
are VIDIOC_G_FBUF
and VIDIOC_S_FBUF
. Thebase
field of structvideo_buffer
remained unchanged, except V4L2defines a flag to indicate non-destructive overlays instead of aNULL
pointer. All other fields moved into thestruct v4l2_pix_formatfmt
substructure ofstruct v4l2_framebuffer. Thedepth
field wasreplaced by pixelformat
. See Section 2.4 for a list of RGB formats and theirrespective color depths.
Instead of the special ioctlsVIDIOCGWIN
and VIDIOCSWIN
V4L2 uses the general-purpose data format negotiation ioctlsVIDIOC_G_FMT
andVIDIOC_S_FMT
. They take a pointer to astruct v4l2_format as argument. Here thewin
member of thefmt
union is used, astruct v4l2_window.
The x
,y
, width
andheight
fields of structvideo_window
moved into struct v4l2_rectsubstructurew
of structv4l2_window
. Thechromakey
,clips
, andclipcount
fields remained unchanged. Structvideo_clip
was renamed to struct v4l2_clip, alsocontaining a structv4l2_rect
, but thesemantics are still the same.
The VIDEO_WINDOW_INTERLACE
flag wasdropped. Instead applications must set thefield
field toV4L2_FIELD_ANY
orV4L2_FIELD_INTERLACED
. TheVIDEO_WINDOW_CHROMAKEY
flag moved intostruct v4l2_framebuffer, under the new nameV4L2_FBUF_FLAG_CHROMAKEY
.
In V4L, storing a bitmap pointer inclips
and settingclipcount
toVIDEO_CLIP_BITMAP
(-1) requests bitmapclipping, using a fixed size bitmap of 1024 × 625 bits. Structv4l2_window
has a separatebitmap
pointer field for this purpose andthe bitmap size is determined byw.width
andw.height
.
The VIDIOCCAPTURE
ioctl to enable ordisable overlay was renamed toVIDIOC_OVERLAY
.
6.1.8. Cropping
To capture only a subsection of the full picture V4Ldefines the VIDIOCGCAPTURE
andVIDIOCSCAPTURE
ioctls using structvideo_capture
. The equivalent V4L2 ioctls areVIDIOC_G_CROP
and VIDIOC_S_CROP
using struct v4l2_crop, and the relatedVIDIOC_CROPCAP
ioctl. This is a rather complex matter, seeSection 1.11 for details.
The x
,y
, width
andheight
fields moved into struct v4l2_rectsubstructurec
of structv4l2_crop
. Thedecimation
field was dropped. In the V4L2API the scaling factor is implied by the size of the croppingrectangle and the size of the captured or overlaid image.
The VIDEO_CAPTURE_ODD
and VIDEO_CAPTURE_EVEN
flags to capture only theodd or even field, respectively, were replaced byV4L2_FIELD_TOP
andV4L2_FIELD_BOTTOM
in the field namedfield
of struct v4l2_pix_format andstruct v4l2_window. These structures are used to select a capture oroverlay format with theVIDIOC_S_FMT
ioctl.
6.1.9. Reading Images, Memory Mapping
6.1.9.1. Capturing using the read method
There is no essential difference between reading imagesfrom a V4L or V4L2 device using theread()
function, however V4L2drivers are not required to support this I/O method. Applications candetermine if the function is available with theVIDIOC_QUERYCAP
ioctl. All V4L2 devices exchanging data with applications must supporttheselect()
andpoll()
functions.
To select an image format and size, V4L provides theVIDIOCSPICT
andVIDIOCSWIN
ioctls. V4L2 uses the general-purpose data format negotiation ioctlsVIDIOC_G_FMT
andVIDIOC_S_FMT
. They take a pointer to astruct v4l2_format as argument, here the struct v4l2_pix_format namedpix
of itsfmt
union is used.
For more information about the V4L2 read interface seeSection 3.1.
6.1.9.2. Capturing using memory mapping
Applications can read from V4L devices by mappingbuffers in device memory, or more often just buffers allocated inDMA-able system memory, into their address space. This avoids the datacopying overhead of the read method. V4L2 supports memory mapping aswell, with a few differences.
V4L | V4L2 |
---|---|
The image format must be selected beforebuffers are allocated, with the VIDIOC_S_FMT ioctl. When no formatis selected the driver may use the last, possibly by anotherapplication requested format. |
|
Applications cannot change the number ofbuffers. The it is built into the driver, unless it has a moduleoption to change the number when the driver module isloaded. |
The |
Drivers map all buffers as one contiguousrange of memory. The |
Buffers are individually mapped. Theoffset and size of each buffer can be determined with the |
The The |
Drivers maintain an incoming and outgoingqueue. |
For a more in-depth discussion of memory mapping andexamples, see Section 3.2.
6.1.10. Reading Raw VBI Data
Originally the V4L API did not specify a raw VBI captureinterface, only the device file/dev/vbi wasreserved for this purpose. The only driver supporting this interfacewas the BTTV driver, de-facto defining the V4L VBI interface. Readingfrom the device yields a raw VBI image with the followingparameters:
struct v4l2_vbi_format | V4L, BTTV driver |
---|---|
sampling_rate | 28636363 Hz NTSC (or any other 525-linestandard); 35468950 Hz PAL and SECAM (625-line standards) |
offset | ? |
samples_per_line | 2048 |
sample_format | V4L2_PIX_FMT_GREY. The last four bytes (amachine endianess integer) contain a frame counter. |
start[] | 10, 273 NTSC; 22, 335 PAL and SECAM |
count[] | 16, 16a |
flags | 0 |
Notes: a. Old driverversions used different values, eventually the custom BTTV_VBISIZE ioctl was added to query thecorrect values. |
Undocumented in the V4L specification, in Linux 2.3 theVIDIOCGVBIFMT
andVIDIOCSVBIFMT
ioctls using structvbi_format
were added to determine the VBIimage parameters. These ioctls are only partially compatible with theV4L2 VBI interface specified inSection 4.7.
An offset
field does notexist, sample_format
is supposed to beVIDEO_PALETTE_RAW
, equivalent toV4L2_PIX_FMT_GREY
. The remaining fields areprobably equivalent to struct v4l2_vbi_format.
Apparently only the Zoran (ZR 36120) driver implementsthese ioctls. The semantics differ from those specified for V4L2 in twoways. The parameters are reset onopen()
andVIDIOCSVBIFMT
always returns anEINVAL error code if theparameters are invalid.
6.1.11. Miscellaneous
V4L2 has no equivalent of theVIDIOCGUNIT
ioctl. Applications can find the VBIdevice associated with a video capture device (or vice versa) byreopening the device and requesting VBI data. For details seeSection 1.1.
No replacement exists for VIDIOCKEY
,and the V4L functions for microcode programming. A new interface forMPEG compression and playback devices is documented inSection 1.9.
6.2. Changes of the V4L2 API
Soon after the V4L API was added to the kernel it wascriticised as too inflexible. In August 1998 Bill Dirks proposed anumber of improvements and began to work on documentation, exampledrivers and applications. With the help of other volunteers thiseventually became the V4L2 API, not just an extension but areplacement for the V4L API. However it took another four years andtwo stable kernel releases until the new API was finally accepted forinclusion into the kernel in its present form.
6.2.1. Early Versions
1998-08-20: First version.
1998-08-27: The select()
function was introduced.
1998-09-10: New video standard interface.
1998-09-18: The VIDIOC_NONCAP
ioctlwas replaced by the otherwise meaninglessO_TRUNC
open()
flag, and the aliasesO_NONCAP
andO_NOIO
were defined. Applications can set thisflag if they intend to access controls only, as opposed to captureapplications which need exclusive access. TheVIDEO_STD_XXX
identifiers are now ordinalsinstead of flags, and the video_std_construct()
helper function takes id and transmission arguments.
1998-09-28: Revamped video standard. Made video controlsindividually enumerable.
1998-10-02: The id
field wasremoved from structvideo_standard
and thecolor subcarrier fields were renamed. TheVIDIOC_QUERYSTD
ioctl wasrenamed toVIDIOC_ENUMSTD
,VIDIOC_G_INPUT
toVIDIOC_ENUMINPUT
. Afirst draft of the Codec API was released.
1998-11-08: Many minor changes. Most symbols have beenrenamed. Some material changes to struct v4l2_capability.
1998-11-12: The read/write directon of some ioctls was misdefined.
1998-11-14: V4L2_PIX_FMT_RGB24
changed to V4L2_PIX_FMT_BGR24
, andV4L2_PIX_FMT_RGB32
changed toV4L2_PIX_FMT_BGR32
. Audio controls are nowaccessible with theVIDIOC_G_CTRL
andVIDIOC_S_CTRL
ioctls undernames starting withV4L2_CID_AUDIO
. TheV4L2_MAJOR
define was removed fromvideodev.h since it was only used once in thevideodev kernel module. TheYUV422
andYUV411
planarimage formats were added.
1998-11-28: A few ioctl symbols changed. Interfaces for codecs andvideo output devices were added.
1999-01-14: A raw VBI capture interface was added.
1999-01-19: The VIDIOC_NEXTBUF
ioctl was removed.
6.2.2. V4L2 Version 0.16 1999-01-31
1999-01-27: There is now one QBUF ioctl, VIDIOC_QWBUF and VIDIOC_QRBUFare gone. VIDIOC_QBUF takes a v4l2_buffer as a parameter. Addeddigital zoom (cropping) controls.
6.2.3. V4L2 Version 0.18 1999-03-16
Added a v4l to V4L2 ioctl compatibility layer tovideodev.c. Driver writers, this changes how you implement your ioctlhandler. See the Driver Writer's Guide. Added some more control idcodes.
6.2.4. V4L2 Version 0.19 1999-06-05
1999-03-18: Fill in the category and catname fields ofv4l2_queryctrl objects before passing them to the driver. Required aminor change to the VIDIOC_QUERYCTRL handlers in the sampledrivers.
1999-03-31: Better compatibility for v4l memory captureioctls. Requires changes to drivers to fully support new compatibilityfeatures, see Driver Writer's Guide and v4l2cap.c. Added new controlIDs: V4L2_CID_HFLIP, _VFLIP. Changed V4L2_PIX_FMT_YUV422P to _YUV422P,and _YUV411P to _YUV411P.
1999-04-04: Added a few more control IDs.
1999-04-07: Added the button control type.
1999-05-02: Fixed a typo in videodev.h, and added theV4L2_CTRL_FLAG_GRAYED (later V4L2_CTRL_FLAG_GRABBED) flag.
1999-05-20: Definition of VIDIOC_G_CTRL was wrong causinga malfunction of this ioctl.
1999-06-05: Changed the value ofV4L2_CID_WHITENESS.
6.2.5. V4L2 Version 0.20 (1999-09-10)
Version 0.20 introduced a number of changes which werenot backward compatible with 0.19 and earlierversions. Purpose of these changes was to simplify the API, whilemaking it more extensible and following common Linux driver APIconventions.
-
Some typos in
V4L2_FMT_FLAG
symbols were fixed. struct v4l2_clip was changed for compatibility withv4l. (1999-08-30) -
V4L2_TUNER_SUB_LANG1
was added.(1999-09-05) -
All ioctl() commands that used an integer argument nowtake a pointer to an integer. Where it makes sense, ioctls will returnthe actual new value in the integer pointed to by the argument, acommon convention in the V4L2 API. The affected ioctls are:VIDIOC_PREVIEW, VIDIOC_STREAMON, VIDIOC_STREAMOFF, VIDIOC_S_FREQ,VIDIOC_S_INPUT, VIDIOC_S_OUTPUT, VIDIOC_S_EFFECT. For example
err = ioctl (fd, VIDIOC_XXX, V4L2_XXX);
becomesint a = V4L2_XXX; err = ioctl(fd, VIDIOC_XXX, &a);
-
All the different get- and set-format commands wereswept into one
VIDIOC_G_FMT
andVIDIOC_S_FMT
ioctl taking a unionand a type field selecting the union member as parameter. Purpose is tosimplify the API by eliminating several ioctls and to allow new anddriver private data streams without adding new ioctls.This change obsoletes the following ioctls:
VIDIOC_S_INFMT
,VIDIOC_G_INFMT
,VIDIOC_S_OUTFMT
,VIDIOC_G_OUTFMT
,VIDIOC_S_VBIFMT
andVIDIOC_G_VBIFMT
. The image format structurev4l2_format
was renamed to struct v4l2_pix_format,while struct v4l2_format is now the envelopping structure for all formatnegotiations. -
Similar to the changes above, the
VIDIOC_G_PARM
andVIDIOC_S_PARM
ioctls were merged withVIDIOC_G_OUTPARM
andVIDIOC_S_OUTPARM
. Atype
field in the new struct v4l2_streamparmselects the respective union member.This change obsoletes the
VIDIOC_G_OUTPARM
andVIDIOC_S_OUTPARM
ioctls. -
Control enumeration was simplified, and two newcontrol flags were introduced and one dropped. The
catname
field was replaced by agroup
field.Drivers can now flag unsupported and temporarilyunavailable controls with
V4L2_CTRL_FLAG_DISABLED
andV4L2_CTRL_FLAG_GRABBED
respectively. Thegroup
name indicates a possibly narrowerclassification than thecategory
. In otherwords, there may be multiple groups within a category. Controls withina group would typically be drawn within a group box. Controls indifferent categories might have a greater separation, or may evenappear in separate windows. -
The struct v4l2_buffer
timestamp
was changed to a 64 bit integer, containing the sampling or outputtime of the frame in nanoseconds. Additionally timestamps will be inabsolute system time, not starting from zero at the beginning of astream. The data type name for timestamps is stamp_t, defined as asigned 64-bit integer. Output devices should not send a buffer outuntil the time in the timestamp field has arrived. I would like tofollow SGI's lead, and adopt a multimedia timestamping system liketheir UST (Unadjusted System Time). Seehttp://reality.sgi.com/cpirazzi_engr/lg/time/intro.html. [This link isno longer valid.] UST uses timestamps that are 64-bit signed integers(not struct timeval's) and given in nanosecond units. The UST clockstarts at zero when the system is booted and runs continuously anduniformly. It takes a little over 292 years for UST to overflow. Thereis no way to set the UST clock. The regular Linux time-of-day clockcan be changed periodically, which would cause errors if it were beingused for timestamping a multimedia stream. A real UST style clock willrequire some support in the kernel that is not there yet. But inanticipation, I will change the timestamp field to a 64-bit integer,and I will change the v4l2_masterclock_gettime() function (used onlyby drivers) to return a 64-bit integer. -
A
sequence
field was addedto struct v4l2_buffer. Thesequence
field countscaptured frames, it is ignored by output devices. When a capturedriver drops a frame, the sequence number of that frame isskipped.
6.2.6. V4L2 Version 0.20 incremental changes
1999-12-23: In struct v4l2_vbi_format thereserved1
field becameoffset
. Previously drivers were required toclear the reserved1
field.
2000-01-13: The V4L2_FMT_FLAG_NOT_INTERLACED
flag was added.
2000-07-31: The linux/poll.h headeris now included byvideodev.h for compatibilitywith the originalvideodev.h file.
2000-11-20: V4L2_TYPE_VBI_OUTPUT
andV4L2_PIX_FMT_Y41P
were added.
2000-11-25: V4L2_TYPE_VBI_INPUT
wasadded.
2000-12-04: A couple typos in symbol names were fixed.
2001-01-18: To avoid namespace conflicts thefourcc
macro defined in thevideodev.h header file was renamed tov4l2_fourcc
.
2001-01-25: A possible driver-level compatibility problembetween the videodev.h file in Linux 2.4.0 andthe videodev.h file included in thevideodevX patch was fixed. Users of an earlierversion ofvideodevX on Linux 2.4.0 shouldrecompile their V4L and V4L2 drivers.
2001-01-26: A possible kernel-level incompatibilitybetween the videodev.h file in thevideodevX patch and thevideodev.h file in Linux 2.2.x with devfs patchesapplied was fixed.
2001-03-02: Certain V4L ioctls which pass data in bothdirection although they are defined with read-only parameter, did notwork correctly through the backward compatibility layer.[Solution?]
2001-04-13: Big endian 16-bit RGB formats were added.
2001-09-17: New YUV formats and the VIDIOC_G_FREQUENCY
andVIDIOC_S_FREQUENCY
ioctls were added. (The oldVIDIOC_G_FREQ
andVIDIOC_S_FREQ
ioctls did not take multiple tunersinto account.)
2000-09-18: V4L2_BUF_TYPE_VBI
wasadded. This maybreak compatibility as theVIDIOC_G_FMT
andVIDIOC_S_FMT
ioctls may fail now if the structv4l2_fmt
type
field does not containV4L2_BUF_TYPE_VBI
. In thedocumentation of the struct v4l2_vbi_formatoffset
field the ambiguous phrase "risingedge" was changed to "leading edge".
6.2.7. V4L2 Version 0.20 2000-11-23
A number of changes were made to the raw VBIinterface.
-
Figures clarifying the line numbering scheme wereadded to the V4L2 API specification. The
start
[0] andstart
[1] fields no longer count linenumbers beginning at zero. Rationale: a) The previous definition wasunclear. b) Thestart
[] values are ordinalnumbers. c) There is no point in inventing a new line numberingscheme. We now use line number as defined by ITU-R, period.Compatibility: Add one to the start values. Applications depending onthe previous semantics may not function correctly. -
The restriction "count[0] > 0 and count[1] > 0"has been relaxed to "(count[0] + count[1]) > 0". Rationale:Drivers may allocate resources at scan line granularity and some dataservices are transmitted only on the first field. The comment thatboth
count
values will usually be equal ismisleading and pointless and has been removed. This changebreaks compatibility with earlier versions:Drivers may return EINVAL, applications may not functioncorrectly. -
Drivers are again permitted to return negative(unknown) start values as proposed earlier. Why this feature wasdropped is unclear. This change maybreakcompatibility with applications depending on the startvalues being positive. The use of
EBUSY
andEINVAL
error codes with theVIDIOC_S_FMT
ioctlwas clarified. TheEBUSY error code was finally documented, and thereserved2
field which was previouslymentioned only in thevideodev.h headerfile. -
New buffer types
V4L2_TYPE_VBI_INPUT
andV4L2_TYPE_VBI_OUTPUT
were added. The former is analias for the oldV4L2_TYPE_VBI
, the latter wasmissing in thevideodev.h file.
6.2.9. V4L2 in Linux 2.5.46, 2002-10
Around October-November 2002, prior to an announcedfeature freeze of Linux 2.5, the API was revised, drawing fromexperience with V4L2 0.20. This unnamed version was finally mergedinto Linux 2.5.46.
-
As specified in Section 1.1.2, driversmust make related device functions available under all minor devicenumbers.
-
The
open()
function requires access modeO_RDWR
regardless of the device type. All V4L2drivers exchanging data with applications must support theO_NONBLOCK
flag. TheO_NOIO
flag, a V4L2 symbol which aliased the meaninglessO_TRUNC
to indicate accesses without dataexchange (panel applications) was dropped. Drivers must stay in "panelmode" until the application attempts to initiate a data exchange, seeSection 1.1. -
The struct v4l2_capability changed dramatically. Note thatalso the size of the structure changed, which is encoded in the ioctlrequest code, thus older V4L2 devices will respond with an EINVAL error code tothe new
VIDIOC_QUERYCAP
ioctl.There are new fields to identify the driver, a new (asof yet unspecified) device function
V4L2_CAP_RDS_CAPTURE
, theV4L2_CAP_AUDIO
flag indicates if the device hasany audio connectors, another I/O capabilityV4L2_CAP_ASYNCIO
can be flagged. In response tothese changes thetype
field became a bitset and was merged into theflags
field.V4L2_FLAG_TUNER
was renamed toV4L2_CAP_TUNER
,V4L2_CAP_VIDEO_OVERLAY
replacedV4L2_FLAG_PREVIEW
andV4L2_CAP_VBI_CAPTURE
andV4L2_CAP_VBI_OUTPUT
replacedV4L2_FLAG_DATA_SERVICE
.V4L2_FLAG_READ
andV4L2_FLAG_WRITE
were merged intoV4L2_CAP_READWRITE
.The redundant fields
inputs
,outputs
andaudios
were removed. These propertiescan be determined as described inSection 1.4 andSection 1.5.The somewhat volatile and therefore barely usefulfields
maxwidth
,maxheight
,minwidth
,minheight
,maxframerate
were removed. This informationis available as described inSection 1.10 andSection 1.7.V4L2_FLAG_SELECT
was removed. Webelieve the select() function is important enough to require supportof it in all V4L2 drivers exchanging data with applications. TheredundantV4L2_FLAG_MONOCHROME
flag was removed,this information is available as described inSection 1.10. -
In struct v4l2_input the
assoc_audio
field and thecapability
field and its only flagV4L2_INPUT_CAP_AUDIO
was replaced by the newaudioset
field. Instead of linking onevideo input to one audio input this field reports all audio inputsthis video input combines with.New fields are
tuner
(reversing the former link from tuners to video inputs),std
andstatus
.Accordingly struct v4l2_output lost its
capability
andassoc_audio
fields.audioset
,modulator
andstd
where added instead. -
The struct v4l2_audio field
audio
was renamed toindex
, for consistency with otherstructures. A new capability flagV4L2_AUDCAP_STEREO
was added to indicated if theaudio input in question supports stereo sound.V4L2_AUDCAP_EFFECTS
and the correspondingV4L2_AUDMODE
flags where removed. This can beeasily implemented using controls. (However the same applies to AVLwhich is still there.)Again for consistency the struct v4l2_audioout field
audio
was renamed toindex
. -
The struct v4l2_tuner
input
field was replaced by anindex
field, permitting devices withmultiple tuners. The link between video inputs and tuners is nowreversed, inputs point to their tuner. Thestd
substructure became asimple set (more about this below) and moved into struct v4l2_input. Atype
field was added.Accordingly in struct v4l2_modulator the
output
was replaced by anindex
field.In struct v4l2_frequency the
port
field was replaced by atuner
field containing the respective tuneror modulator index number. A tunertype
field was added and thereserved
fieldbecame larger for future extensions (satellite tuners inparticular). -
The idea of completely transparent video standards wasdropped. Experience showed that applications must be able to work withvideo standards beyond presenting the user a menu. Instead ofenumerating supported standards with an ioctl applications can nowrefer to standards by v4l2_std_id and symbols defined in thevideodev2.h header file. For details seeSection 1.7. The
VIDIOC_G_STD
andVIDIOC_S_STD
now take a pointer to this type as argument.VIDIOC_QUERYSTD
was added to autodetect the received standard, ifthe hardware has this capability. In struct v4l2_standard anindex
field was added forVIDIOC_ENUMSTD
.Av4l2_std_id field namedid
was added asmachine readable identifier, also replacing thetransmission
field. The misleadingframerate
field was renamedtoframeperiod
. The now obsoletecolorstandard
information, originallyneeded to distguish between variations of standards, wereremoved.Struct
v4l2_enumstd
ceased tobe.VIDIOC_ENUMSTD
now takes a pointer to a struct v4l2_standarddirectly. The information which standards are supported by aparticular video input or output moved into struct v4l2_input andstruct v4l2_output fields namedstd
,respectively. -
The struct v4l2_queryctrl fields
category
andgroup
did not catch on and/or were notimplemented as expected and therefore removed. -
The
VIDIOC_TRY_FMT
ioctl was added to negotiate dataformats as withVIDIOC_S_FMT
, but without the overhead ofprogramming the hardware and regardless of I/O in progress.In struct v4l2_format the
fmt
union was extended to contain struct v4l2_window. All image formatnegotiations are now possible withVIDIOC_G_FMT
,VIDIOC_S_FMT
andVIDIOC_TRY_FMT
; ioctl. TheVIDIOC_G_WIN
andVIDIOC_S_WIN
ioctls to prepare for a videooverlay were removed. Thetype
fieldchanged to type enum v4l2_buf_type and the buffer type names changed asfollows.Old defines enum v4l2_buf_type V4L2_BUF_TYPE_CAPTURE
V4L2_BUF_TYPE_VIDEO_CAPTURE
V4L2_BUF_TYPE_CODECIN
Omitted for now V4L2_BUF_TYPE_CODECOUT
Omitted for now V4L2_BUF_TYPE_EFFECTSIN
Omitted for now V4L2_BUF_TYPE_EFFECTSIN2
Omitted for now V4L2_BUF_TYPE_EFFECTSOUT
Omitted for now V4L2_BUF_TYPE_VIDEOOUT
V4L2_BUF_TYPE_VIDEO_OUTPUT
-
V4L2_BUF_TYPE_VIDEO_OVERLAY
-
V4L2_BUF_TYPE_VBI_CAPTURE
-
V4L2_BUF_TYPE_VBI_OUTPUT
-
V4L2_BUF_TYPE_SLICED_VBI_CAPTURE
-
V4L2_BUF_TYPE_SLICED_VBI_OUTPUT
V4L2_BUF_TYPE_PRIVATE_BASE
V4L2_BUF_TYPE_PRIVATE
-
In struct v4l2_fmtdesc a enum v4l2_buf_type field named
type
was added as in struct v4l2_format. TheVIDIOC_ENUM_FBUFFMT
ioctl is no longer needed andwas removed. These calls can be replaced byVIDIOC_ENUM_FMT
withtypeV4L2_BUF_TYPE_VIDEO_OVERLAY
. -
In struct v4l2_pix_format the
depth
field was removed, assumingapplications which recognize the format by its four-character-codealready know the color depth, and others do not care about it. Thesame rationale lead to the removal of theV4L2_FMT_FLAG_COMPRESSED
flag. TheV4L2_FMT_FLAG_SWCONVECOMPRESSED
flag was removedbecause drivers are not supposed to convert images in kernel space. Auser library of conversion functions should be provided instead. TheV4L2_FMT_FLAG_BYTESPERLINE
flag was redundant.Applications can set thebytesperline
fieldto zero to get a reasonable default. Since the remaining flags werereplaced as well, theflags
field itselfwas removed.The interlace flags were replaced by a enum v4l2_fieldvalue in a newly added
field
field.Old flag enum v4l2_field V4L2_FMT_FLAG_NOT_INTERLACED
? V4L2_FMT_FLAG_INTERLACED
=V4L2_FMT_FLAG_COMBINED
V4L2_FIELD_INTERLACED
V4L2_FMT_FLAG_TOPFIELD
=V4L2_FMT_FLAG_ODDFIELD
V4L2_FIELD_TOP
V4L2_FMT_FLAG_BOTFIELD
=V4L2_FMT_FLAG_EVENFIELD
V4L2_FIELD_BOTTOM
-
V4L2_FIELD_SEQ_TB
-
V4L2_FIELD_SEQ_BT
-
V4L2_FIELD_ALTERNATE
The color space flags were replaced by aenum v4l2_colorspace value in a newly added
colorspace
field, where one ofV4L2_COLORSPACE_SMPTE170M
,V4L2_COLORSPACE_BT878
,V4L2_COLORSPACE_470_SYSTEM_M
orV4L2_COLORSPACE_470_SYSTEM_BG
replacesV4L2_FMT_CS_601YUV
. -
In struct v4l2_requestbuffers the
type
field was properly defined asenum v4l2_buf_type. Buffer types changed as mentioned above. A newmemory
field of type enum v4l2_memory wasadded to distinguish between I/O methods using buffers allocatedby the driver or the application. See Chapter 3 fordetails. -
In struct v4l2_buffer the
type
field was properly defined as enum v4l2_buf_type. Buffer types changed asmentioned above. Afield
field of typeenum v4l2_field was added to indicate if a buffer contains a top orbottom field. The old field flags were removed. Since no unadjustedsystem time clock was added to the kernel as planned, thetimestamp
field changed back from typestamp_t, an unsigned 64 bit integer expressing the sample time innanoseconds, to structtimeval
. With theaddition of a second memory mapping method theoffset
field moved into unionm
, and a newmemory
field of type enum v4l2_memory wasadded to distinguish between I/O methods. SeeChapter 3for details.The
V4L2_BUF_REQ_CONTIG
flag was used by the V4L compatibility layer, after changes to thiscode it was no longer needed. TheV4L2_BUF_ATTR_DEVICEMEM
flag would indicate ifthe buffer was indeed allocated in device memory rather than DMA-ablesystem memory. It was barely useful and so was removed. -
In struct v4l2_framebuffer the
base[3]
array anticipating double- andtriple-buffering in off-screen video memory, however without defininga synchronization mechanism, was replaced by a single pointer. TheV4L2_FBUF_CAP_SCALEUP
andV4L2_FBUF_CAP_SCALEDOWN
flags were removed.Applications can determine this capability more accurately using thenew cropping and scaling interface. TheV4L2_FBUF_CAP_CLIPPING
flag was replaced byV4L2_FBUF_CAP_LIST_CLIPPING
andV4L2_FBUF_CAP_BITMAP_CLIPPING
. -
In struct v4l2_clip the
x
,y
,width
andheight
field moved into ac
substructure of type struct v4l2_rect. Thex
andy
fieldswere renamed toleft
andtop
, i. e. offsets to a context dependentorigin. -
In struct v4l2_window the
x
,y
,width
andheight
field moved into aw
substructure as above. Afield
field of type %v4l2-field; was addedto distinguish between field and frame (interlaced) overlay. -
The digital zoom interface, including struct
v4l2_zoomcap
, structv4l2_zoom
,V4L2_ZOOM_NONCAP
andV4L2_ZOOM_WHILESTREAMING
was replaced by a newcropping and scaling interface. The previously unused structv4l2_cropcap
andv4l2_crop
where redefined for this purpose.SeeSection 1.11 for details. -
In struct v4l2_vbi_format the
SAMPLE_FORMAT
field now contains afour-character-code as used to identify video image formats andV4L2_PIX_FMT_GREY
replaces theV4L2_VBI_SF_UBYTE
define. Thereserved
field was extended. -
In struct v4l2_captureparm the type of the
timeperframe
field changed from unsignedlong to struct v4l2_fract. This allows the accurate expression of multiplesof the NTSC-M frame rate 30000 / 1001. A new fieldreadbuffers
was added to control the driverbehaviour in read I/O mode.Similar changes were made to struct v4l2_outputparm.
-
The struct
v4l2_performance
andVIDIOC_G_PERF
ioctl were dropped. Except whenusing the read/write I/O method, which islimited anyway, this information is already available toapplications. -
The example transformation from RGB to YCbCr colorspace in the old V4L2 documentation was inaccurate, this has beencorrected inChapter 2.
6.2.10. V4L2 2003-06-19
-
A new capability flag
V4L2_CAP_RADIO
was added for radio devices. Priorto this change radio devices would identify solely by having exactly onetuner whose type field readsV4L2_TUNER_RADIO
. -
An optional driver access priority mechanism wasadded, see Section 1.3 for details.
-
The audio input and output interface was found to beincomplete.
Previously the
VIDIOC_G_AUDIO
ioctl would enumerate the available audio inputs. An ioctl todetermine the current audio input, if more than one combines with thecurrent video input, did not exist. SoVIDIOC_G_AUDIO
was renamed toVIDIOC_G_AUDIO_OLD
, this ioctl will be removed inthe future. TheVIDIOC_ENUMAUDIO
ioctl was added to enumerateaudio inputs, whileVIDIOC_G_AUDIO
now reports the current audioinput.The same changes were made to
VIDIOC_G_AUDOUT
andVIDIOC_ENUMAUDOUT
.Until further the "videodev" module will automaticallytranslate between the old and new ioctls, but drivers and applicationsmust be updated to successfully compile again.
-
The
VIDIOC_OVERLAY
ioctl was incorrectly defined withwrite-read parameter. It was changed to write-only, while the write-readversion was renamed toVIDIOC_OVERLAY_OLD
. The oldioctl will be removed in the future. Until further the "videodev"kernel module will automatically translate to the new version, so driversmust be recompiled, but not applications. -
Section 4.2 incorrectly stated thatclipping rectangles define regions where the video can be seen.Correct is that clipping rectangles define regions whereno video shall be displayed and so the graphicssurface can be seen.
-
The
VIDIOC_S_PARM
andVIDIOC_S_CTRL
ioctls weredefined with write-only parameter, inconsistent with other ioctlsmodifying their argument. They were changed to write-read, while a_OLD
suffix was added to the write-only versions.The old ioctls will be removed in the future. Drivers andapplications assuming a constant parameter need an update.
6.2.11. V4L2 2003-11-05
-
In Section 2.4 the following pixelformats were incorrectly transferred from Bill Dirks' V4L2specification. Descriptions below refer to bytes in memory, inascending address order.
Symbol In this document prior to revision0.5 Corrected V4L2_PIX_FMT_RGB24
B, G, R R, G, B V4L2_PIX_FMT_BGR24
R, G, B B, G, R V4L2_PIX_FMT_RGB32
B, G, R, X R, G, B, X V4L2_PIX_FMT_BGR32
R, G, B, X B, G, R, X V4L2_PIX_FMT_BGR24
example was alwayscorrect.In Section 6.1.5 the mappingof the V4L
VIDEO_PALETTE_RGB24
andVIDEO_PALETTE_RGB32
formats to V4L2 pixel formatswas accordingly corrected. -
Unrelated to the fixes above, drivers may stillinterpret some V4L2 RGB pixel formats differently. These issues haveyet to be addressed, for details seeSection 2.4.
6.2.12. V4L2 in Linux 2.6.6, 2004-05-09
-
The
VIDIOC_CROPCAP
ioctl was incorrectly definedwith read-only parameter. It is now defined as write-read ioctl, whilethe read-only version was renamed toVIDIOC_CROPCAP_OLD
. The old ioctl will be removedin the future.
6.2.13. V4L2 in Linux 2.6.8
-
A new field
input
(formerreserved[0]
) was added to the struct v4l2_bufferstructure. Purpose of this field is to alternate between video inputs(e. g. cameras) in step with the video capturing process. This functionmust be enabled with the newV4L2_BUF_FLAG_INPUT
flag. Theflags
field is no longerread-only.
6.2.14. V4L2 spec erratum 2004-08-01
-
The return value of theV4L2 open()(2) function was incorrectly documented.
-
Audio output ioctls end in -AUDOUT, not -AUDIOOUT.
-
In the Current Audio Input example the
VIDIOC_G_AUDIO
ioctl took the wrongargument. -
The documentation of the
VIDIOC_QBUF
andVIDIOC_DQBUF
ioctls did not mention the struct v4l2_buffermemory
field. It was also missing fromexamples. Also on theVIDIOC_DQBUF
page theEIO error codewas not documented.
6.2.15. V4L2 in Linux 2.6.14
-
A new sliced VBI interface was added. It is documentedin Section 4.8 and replaces the interface firstproposed in V4L2 specification 0.8.
6.2.16. V4L2 in Linux 2.6.15
-
The
VIDIOC_LOG_STATUS
ioctl was added. -
New video standards
V4L2_STD_NTSC_443
,V4L2_STD_SECAM_LC
,V4L2_STD_SECAM_DK
(a set of SECAM D, K and K1),andV4L2_STD_ATSC
(a set ofV4L2_STD_ATSC_8_VSB
andV4L2_STD_ATSC_16_VSB
) were defined. Note theV4L2_STD_525_60
set now includesV4L2_STD_NTSC_443
. See alsoTable 3. -
The
VIDIOC_G_COMP
andVIDIOC_S_COMP
ioctl were renamed toVIDIOC_G_MPEGCOMP
andVIDIOC_S_MPEGCOMP
respectively. Their argumentwas replaced by a structv4l2_mpeg_compression
pointer. (TheVIDIOC_G_MPEGCOMP
andVIDIOC_S_MPEGCOMP
ioctls where removed in Linux2.6.25.)
6.2.17. V4L2 spec erratum 2005-11-27
The capture example in Appendix Bcalled the VIDIOC_S_CROP
ioctl without checking if cropping issupported. In the video standard selection example inSection 1.7 theVIDIOC_S_STD
call used the wrongargument type.
6.2.18. V4L2 spec erratum 2006-01-10
-
The
V4L2_IN_ST_COLOR_KILL
flag instruct v4l2_input not only indicates if the color killer is enabled, butalso if it is active. (The color killer disables color decoding whenit detects no color in the video signal to improve the imagequality.) -
VIDIOC_S_PARM
is a write-read ioctl, not write-only asstated on its reference page. The ioctl changed in 2003 as noted above.
6.2.19. V4L2 spec erratum 2006-02-03
-
In struct v4l2_captureparm and struct v4l2_outputparm the
timeperframe
field gives the time inseconds, not microseconds.
6.2.20. V4L2 spec erratum 2006-02-04
-
The
clips
field instruct v4l2_window must point to an array of struct v4l2_clip, not a linkedlist, because drivers ignore the structv4l2_clip
.next
pointer.
6.2.21. V4L2 in Linux 2.6.17
-
New video standard macros were added:
V4L2_STD_NTSC_M_KR
(NTSC M South Korea), and thesetsV4L2_STD_MN
,V4L2_STD_B
,V4L2_STD_GH
andV4L2_STD_DK
. TheV4L2_STD_NTSC
andV4L2_STD_SECAM
sets now includeV4L2_STD_NTSC_M_KR
andV4L2_STD_SECAM_LC
respectively. -
A new
V4L2_TUNER_MODE_LANG1_LANG2
was defined to record both languages of a bilingual program. Theuse ofV4L2_TUNER_MODE_STEREO
for this purposeis deprecated now. See theVIDIOC_G_TUNER
section fordetails.
6.2.22. V4L2 spec erratum 2006-09-23 (Draft 0.15)
-
In various places
V4L2_BUF_TYPE_SLICED_VBI_CAPTURE
andV4L2_BUF_TYPE_SLICED_VBI_OUTPUT
of the sliced VBIinterface were not mentioned along with other buffer types. -
In ioctl VIDIOC_G_AUDIO, VIDIOC_S_AUDIO(2) it was clarifiedthat the struct v4l2_audio
mode
field is a flagsfield. -
ioctl VIDIOC_QUERYCAP(2) did not mention thesliced VBI and radio capability flags.
-
In ioctl VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY(2) it wasclarified that applications must initialize the tuner
type
field of struct v4l2_frequency beforecallingVIDIOC_S_FREQUENCY
. -
The
reserved
arrayin struct v4l2_requestbuffers has 2 elements, not 32. -
In Section 4.3 andSection 4.7 the device file names/dev/vout which never caught on were replacedby/dev/video.
-
With Linux 2.6.15 the possible range for VBI device minornumbers was extended from 224-239 to 224-255. Accordingly device file names/dev/vbi0 to/dev/vbi31 arepossible now.
6.2.23. V4L2 in Linux 2.6.18
-
New ioctls
VIDIOC_G_EXT_CTRLS
,VIDIOC_S_EXT_CTRLS
andVIDIOC_TRY_EXT_CTRLS
were added, a flag to skip unsupportedcontrols withVIDIOC_QUERYCTRL
, new control typesV4L2_CTRL_TYPE_INTEGER64
andV4L2_CTRL_TYPE_CTRL_CLASS
(Table 3), and new control flagsV4L2_CTRL_FLAG_READ_ONLY
,V4L2_CTRL_FLAG_UPDATE
,V4L2_CTRL_FLAG_INACTIVE
andV4L2_CTRL_FLAG_SLIDER
(Table 4). SeeSection 1.9 for details.
6.2.24. V4L2 in Linux 2.6.19
-
In struct v4l2_sliced_vbi_cap a buffer type field was addedreplacing a reserved field. Note on architectures where the size ofenum types differs from int types the size of the structure changed.The
VIDIOC_G_SLICED_VBI_CAP
ioctl was redefined from being read-onlyto write-read. Applications must initialize the type field and clearthe reserved fields now. These changes maybreak thecompatibility with older drivers and applications. -
The ioctls
VIDIOC_ENUM_FRAMESIZES
andVIDIOC_ENUM_FRAMEINTERVALS
were added. -
A new pixel format
V4L2_PIX_FMT_RGB444
(Table 2-1) was added.
6.2.25. V4L2 spec erratum 2006-10-12 (Draft 0.17)
-
V4L2_PIX_FMT_HM12
(Table 2-8) is a YUV 4:2:0, not 4:2:2 format.
6.2.26. V4L2 in Linux 2.6.21
-
The videodev2.h header file isnow dual licensed under GNU General Public License version two orlater, and under a 3-clause BSD-style license.
6.2.27. V4L2 in Linux 2.6.22
-
Two new field orders
V4L2_FIELD_INTERLACED_TB
andV4L2_FIELD_INTERLACED_BT
were added. SeeTable 3-8 for details. -
Three new clipping/blending methods with a global orstraight or inverted local alpha value were added to the video overlayinterface. See the description of the
VIDIOC_G_FBUF
andVIDIOC_S_FBUF
ioctls for details.A new
global_alpha
fieldwas added tov4l2_window
,extending the structure. This maybreakcompatibility with applications using a structv4l2_window
directly. However theVIDIOC_G/S/TRY_FMT ioctls, which take apointer to av4l2_format parentstructure with padding bytes at the end, are not affected. -
The format of the
chromakey
field in struct v4l2_window changed from "host order RGB32" to a pixelvalue in the same format as the framebuffer. This may breakcompatibility with existing applications. Driverssupporting the "host order RGB32" format are not known.
6.2.28. V4L2 in Linux 2.6.24
-
The pixel formats
V4L2_PIX_FMT_PAL8
,V4L2_PIX_FMT_YUV444
,V4L2_PIX_FMT_YUV555
,V4L2_PIX_FMT_YUV565
andV4L2_PIX_FMT_YUV32
were added.
6.2.29. V4L2 in Linux 2.6.25
-
The pixel formats
V4L2_PIX_FMT_Y16
andV4L2_PIX_FMT_SBGGR16
were added. -
New controls
V4L2_CID_POWER_LINE_FREQUENCY
,V4L2_CID_HUE_AUTO
,V4L2_CID_WHITE_BALANCE_TEMPERATURE
,V4L2_CID_SHARPNESS
andV4L2_CID_BACKLIGHT_COMPENSATION
were added. ThecontrolsV4L2_CID_BLACK_LEVEL
,V4L2_CID_WHITENESS
,V4L2_CID_HCENTER
andV4L2_CID_VCENTER
were deprecated. -
A Camera controlsclass was added, with the new controls
V4L2_CID_EXPOSURE_AUTO
,V4L2_CID_EXPOSURE_ABSOLUTE
,V4L2_CID_EXPOSURE_AUTO_PRIORITY
,V4L2_CID_PAN_RELATIVE
,V4L2_CID_TILT_RELATIVE
,V4L2_CID_PAN_RESET
,V4L2_CID_TILT_RESET
,V4L2_CID_PAN_ABSOLUTE
,V4L2_CID_TILT_ABSOLUTE
,V4L2_CID_FOCUS_ABSOLUTE
,V4L2_CID_FOCUS_RELATIVE
andV4L2_CID_FOCUS_AUTO
. -
The
VIDIOC_G_MPEGCOMP
andVIDIOC_S_MPEGCOMP
ioctls, which were supersededby theextended controlsinterface in Linux 2.6.18, where finally removed from thevideodev2.h header file.
6.3. Relation of V4L2 to other Linux multimedia APIs
6.3.1. X Video Extension
The X Video Extension (abbreviated XVideo or just Xv) isan extension of the X Window system, implemented for example by theXFree86 project. Its scope is similar to V4L2, an API to video captureand output devices for X clients. Xv allows applications to displaylive video in a window, send window contents to a TV output, andcapture or output still images in XPixmaps[27]. With their implementation XFree86 makes theextension available across many operating systems andarchitectures.
Because the driver is embedded into the X server Xv has anumber of advantages over the V4L2videooverlay interface. The driver can easily determine the overlaytarget, i. e. visible graphics memory or off-screen buffers for adestructive overlay. It can program the RAMDAC for a non-destructiveoverlay, scaling or color-keying, or the clipping functions of thevideo capture hardware, always in sync with drawing operations orwindows moving or changing their stacking order.
To combine the advantages of Xv and V4L a special Xvdriver exists in XFree86 and XOrg, just programming any overlay capableVideo4Linux device it finds. To enable it/etc/X11/XF86Config must contain these lines:
Section "Module" Load "v4l" EndSection
As of XFree86 4.2 this driver still supports only V4Lioctls, however it should work just fine with all V4L2 devices throughthe V4L2 backward-compatibility layer. Since V4L2 permits multipleopens it is possible (if supported by the V4L2 driver) to capturevideo while an X client requested video overlay. Restrictions ofsimultaneous capturing and overlay are discussed inSection 4.2 apply.
Only marginally related to V4L2, XFree86 extended Xv tosupport hardware YUV to RGB conversion and scaling for faster videoplayback, and added an interface to MPEG-2 decoding hardware. This APIis useful to display images captured with V4L2 devices.
6.3.2. Digital Video
V4L2 does not support digital terrestrial, cable orsatellite broadcast. A separate project aiming at digital receiversexists. You can find its homepage athttp://linuxtv.org. The Linux DVB APIhas no connection to the V4L2 API except that drivers for hybridhardware may support both.
6.4. Experimental API Elements
The following V4L2 API elements are currently experimentaland may change in the future.
-
Video Output Overlay (OSD) Interface, Section 4.4.
-
V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY
, enum v4l2_buf_type,Table 3-2. -
V4L2_CAP_VIDEO_OUTPUT_OVERLAY
,VIDIOC_QUERYCAP
ioctl,Table 2. -
VIDIOC_ENUM_FRAMESIZES
andVIDIOC_ENUM_FRAMEINTERVALS
ioctls. -
VIDIOC_G_ENC_INDEX
ioctl. -
VIDIOC_ENCODER_CMD
andVIDIOC_TRY_ENCODER_CMD
ioctls. -
VIDIOC_DBG_G_REGISTER
andVIDIOC_DBG_S_REGISTER
ioctls. -
VIDIOC_G_CHIP_IDENT
ioctl.
6.5. Obsolete API Elements
The following V4L2 API elements were superseded by newinterfaces and should not be implemented in new drivers.
-
VIDIOC_G_MPEGCOMP
andVIDIOC_S_MPEGCOMP
ioctls. Use Extended Controls,Section 1.9.
Appendix A. Video For Linux Two Header File
/* * Video for Linux Two header file * * Copyright (C) 1999-2007 the contributors * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * Alternatively you can redistribute this file under the terms of the * BSD license as stated below: * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * 3. The names of its contributors may not be used to endorse or promote * products derived from this software without specific prior written * permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED * TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. * * Header file for v4l or V4L2 drivers and applications * with public API. * All kernel-specific stuff were moved to media/v4l2-dev.h, so * no #if __KERNEL tests are allowed here * * See http://linuxtv.org for more info * * Author: Bill Dirks <bill@thedirks.org> * Justin Schoeman * Hans Verkuil <hverkuil@xs4all.nl> * et al. */ #ifndef __LINUX_VIDEODEV2_H #define __LINUX_VIDEODEV2_H #ifdef __KERNEL__ #include <linux/time.h> /* need struct timeval */ #include <linux/compiler.h> /* need __user */ #else #define __user #include <sys/time.h> #endif #include <linux/ioctl.h> #include <linux/types.h> /* * Common stuff for both V4L1 and V4L2 * Moved from videodev.h */ #define VIDEO_MAX_FRAME 32 #define VID_TYPE_CAPTURE 1 /* Can capture */ #define VID_TYPE_TUNER 2 /* Can tune */ #define VID_TYPE_TELETEXT 4 /* Does teletext */ #define VID_TYPE_OVERLAY 8 /* Overlay onto frame buffer */ #define VID_TYPE_CHROMAKEY 16 /* Overlay by chromakey */ #define VID_TYPE_CLIPPING 32 /* Can clip */ #define VID_TYPE_FRAMERAM 64 /* Uses the frame buffer memory */ #define VID_TYPE_SCALES 128 /* Scalable */ #define VID_TYPE_MONOCHROME 256 /* Monochrome only */ #define VID_TYPE_SUBCAPTURE 512 /* Can capture subareas of the image */ #define VID_TYPE_MPEG_DECODER 1024 /* Can decode MPEG streams */ #define VID_TYPE_MPEG_ENCODER 2048 /* Can encode MPEG streams */ #define VID_TYPE_MJPEG_DECODER 4096 /* Can decode MJPEG streams */ #define VID_TYPE_MJPEG_ENCODER 8192 /* Can encode MJPEG streams */ /* * M I S C E L L A N E O U S */ /* Four-character-code (FOURCC) */ #define v4l2_fourcc(a,b,c,d)\ (((__u32)(a)<<0)|((__u32)(b)<<8)|((__u32)(c)<<16)|((__u32)(d)<<24)) /* * E N U M S */ enum v4l2_field { V4L2_FIELD_ANY = 0, /* driver can choose from none, top, bottom, interlaced depending on whatever it thinks is approximate ... */ V4L2_FIELD_NONE = 1, /* this device has no fields ... */ V4L2_FIELD_TOP = 2, /* top field only */ V4L2_FIELD_BOTTOM = 3, /* bottom field only */ V4L2_FIELD_INTERLACED = 4, /* both fields interlaced */ V4L2_FIELD_SEQ_TB = 5, /* both fields sequential into one buffer, top-bottom order */ V4L2_FIELD_SEQ_BT = 6, /* same as above + bottom-top order */ V4L2_FIELD_ALTERNATE = 7, /* both fields alternating into separate buffers */ V4L2_FIELD_INTERLACED_TB = 8, /* both fields interlaced, top field first and the top field is transmitted first */ V4L2_FIELD_INTERLACED_BT = 9, /* both fields interlaced, top field first and the bottom field is transmitted first */ }; #define V4L2_FIELD_HAS_TOP(field) \ ((field) == V4L2_FIELD_TOP ||\ (field) == V4L2_FIELD_INTERLACED ||\ (field) == V4L2_FIELD_INTERLACED_TB ||\ (field) == V4L2_FIELD_INTERLACED_BT ||\ (field) == V4L2_FIELD_SEQ_TB ||\ (field) == V4L2_FIELD_SEQ_BT) #define V4L2_FIELD_HAS_BOTTOM(field) \ ((field) == V4L2_FIELD_BOTTOM ||\ (field) == V4L2_FIELD_INTERLACED ||\ (field) == V4L2_FIELD_INTERLACED_TB ||\ (field) == V4L2_FIELD_INTERLACED_BT ||\ (field) == V4L2_FIELD_SEQ_TB ||\ (field) == V4L2_FIELD_SEQ_BT) #define V4L2_FIELD_HAS_BOTH(field) \ ((field) == V4L2_FIELD_INTERLACED ||\ (field) == V4L2_FIELD_INTERLACED_TB ||\ (field) == V4L2_FIELD_INTERLACED_BT ||\ (field) == V4L2_FIELD_SEQ_TB ||\ (field) == V4L2_FIELD_SEQ_BT) enum v4l2_buf_type { V4L2_BUF_TYPE_VIDEO_CAPTURE = 1, V4L2_BUF_TYPE_VIDEO_OUTPUT = 2, V4L2_BUF_TYPE_VIDEO_OVERLAY = 3, V4L2_BUF_TYPE_VBI_CAPTURE = 4, V4L2_BUF_TYPE_VBI_OUTPUT = 5, V4L2_BUF_TYPE_SLICED_VBI_CAPTURE = 6, V4L2_BUF_TYPE_SLICED_VBI_OUTPUT = 7, #if 1 /*KEEP*/ /* Experimental */ V4L2_BUF_TYPE_VIDEO_OUTPUT_OVERLAY = 8, #endif V4L2_BUF_TYPE_PRIVATE = 0x80, }; enum v4l2_ctrl_type { V4L2_CTRL_TYPE_INTEGER = 1, V4L2_CTRL_TYPE_BOOLEAN = 2, V4L2_CTRL_TYPE_MENU = 3, V4L2_CTRL_TYPE_BUTTON = 4, V4L2_CTRL_TYPE_INTEGER64 = 5, V4L2_CTRL_TYPE_CTRL_CLASS = 6, }; enum v4l2_tuner_type { V4L2_TUNER_RADIO = 1, V4L2_TUNER_ANALOG_TV = 2, V4L2_TUNER_DIGITAL_TV = 3, }; enum v4l2_memory { V4L2_MEMORY_MMAP = 1, V4L2_MEMORY_USERPTR = 2, V4L2_MEMORY_OVERLAY = 3, }; /* see also http://vektor.theorem.ca/graphics/ycbcr/ */ enum v4l2_colorspace { /* ITU-R 601 -- broadcast NTSC/PAL */ V4L2_COLORSPACE_SMPTE170M = 1, /* 1125-Line (US) HDTV */ V4L2_COLORSPACE_SMPTE240M = 2, /* HD and modern captures. */ V4L2_COLORSPACE_REC709 = 3, /* broken BT878 extents (601, luma range 16-253 instead of 16-235) */ V4L2_COLORSPACE_BT878 = 4, /* These should be useful. Assume 601 extents. */ V4L2_COLORSPACE_470_SYSTEM_M = 5, V4L2_COLORSPACE_470_SYSTEM_BG = 6, /* I know there will be cameras that send this. So, this is * unspecified chromaticities and full 0-255 on each of the * Y'CbCr components */ V4L2_COLORSPACE_JPEG = 7, /* For RGB colourspaces, this is probably a good start. */ V4L2_COLORSPACE_SRGB = 8, }; enum v4l2_priority { V4L2_PRIORITY_UNSET = 0, /* not initialized */ V4L2_PRIORITY_BACKGROUND = 1, V4L2_PRIORITY_INTERACTIVE = 2, V4L2_PRIORITY_RECORD = 3, V4L2_PRIORITY_DEFAULT = V4L2_PRIORITY_INTERACTIVE, }; struct v4l2_rect { __s32 left; __s32 top; __s32 width; __s32 height; }; struct v4l2_fract { __u32 numerator; __u32 denominator; }; /* * D R I V E R C A P A B I L I T I E S */ struct v4l2_capability { __u8 driver[16]; /* i.e.ie; "bttv" */ __u8 card[32]; /* i.e.ie; "Hauppauge WinTV" */ __u8 bus_info[32]; /* "PCI:" + pci_name(pci_dev) */ __u32 version; /* should use KERNEL_VERSION() */ __u32 capabilities; /* Device capabilities */ __u32 reserved[4]; }; /* Values for 'capabilities' field */ #define V4L2_CAP_VIDEO_CAPTURE 0x00000001 /* Is a video capture device */ #define V4L2_CAP_VIDEO_OUTPUT 0x00000002 /* Is a video output device */ #define V4L2_CAP_VIDEO_OVERLAY 0x00000004 /* Can do video overlay */ #define V4L2_CAP_VBI_CAPTURE 0x00000010 /* Is a raw VBI capture device */ #define V4L2_CAP_VBI_OUTPUT 0x00000020 /* Is a raw VBI output device */ #define V4L2_CAP_SLICED_VBI_CAPTURE 0x00000040 /* Is a sliced VBI capture device */ #define V4L2_CAP_SLICED_VBI_OUTPUT 0x00000080 /* Is a sliced VBI output device */ #define V4L2_CAP_RDS_CAPTURE 0x00000100 /* RDS data capture */ #define V4L2_CAP_VIDEO_OUTPUT_OVERLAY 0x00000200 /* Can do video output overlay */ #define V4L2_CAP_TUNER 0x00010000 /* has a tuner */ #define V4L2_CAP_AUDIO 0x00020000 /* has audio support */ #define V4L2_CAP_RADIO 0x00040000 /* is a radio device */ #define V4L2_CAP_READWRITE 0x01000000 /* read/write systemcalls */ #define V4L2_CAP_ASYNCIO 0x02000000 /* async I/O */ #define V4L2_CAP_STREAMING 0x04000000 /* streaming I/O ioctls */ /* * V I D E O I M A G E F O R M A T */ struct v4l2_pix_format { __u32 width; __u32 height; __u32 pixelformat; enum v4l2_field field; __u32 bytesperline; /* for padding, zero if unused */ __u32 sizeimage; enum v4l2_colorspace colorspace; __u32 priv; /* private data, depends on pixelformat */ }; /* Pixel format FOURCC depth Description */ #define V4L2_PIX_FMT_RGB332 v4l2_fourcc('R','G','B','1') /* 8 RGB-3-3-2 */ #define V4L2_PIX_FMT_RGB444 v4l2_fourcc('R','4','4','4') /* 16 xxxxrrrr ggggbbbb */ #define V4L2_PIX_FMT_RGB555 v4l2_fourcc('R','G','B','O') /* 16 RGB-5-5-5 */ #define V4L2_PIX_FMT_RGB565 v4l2_fourcc('R','G','B','P') /* 16 RGB-5-6-5 */ #define V4L2_PIX_FMT_RGB555X v4l2_fourcc('R','G','B','Q') /* 16 RGB-5-5-5 BE */ #define V4L2_PIX_FMT_RGB565X v4l2_fourcc('R','G','B','R') /* 16 RGB-5-6-5 BE */ #define V4L2_PIX_FMT_BGR24 v4l2_fourcc('B','G','R','3') /* 24 BGR-8-8-8 */ #define V4L2_PIX_FMT_RGB24 v4l2_fourcc('R','G','B','3') /* 24 RGB-8-8-8 */ #define V4L2_PIX_FMT_BGR32 v4l2_fourcc('B','G','R','4') /* 32 BGR-8-8-8-8 */ #define V4L2_PIX_FMT_RGB32 v4l2_fourcc('R','G','B','4') /* 32 RGB-8-8-8-8 */ #define V4L2_PIX_FMT_GREY v4l2_fourcc('G','R','E','Y') /* 8 Greyscale */ #define V4L2_PIX_FMT_Y16 v4l2_fourcc('Y','1','6',' ') /* 16 Greyscale */ #define V4L2_PIX_FMT_PAL8 v4l2_fourcc('P','A','L','8') /* 8 8-bit palette */ #define V4L2_PIX_FMT_YVU410 v4l2_fourcc('Y','V','U','9') /* 9 YVU 4:1:0 */ #define V4L2_PIX_FMT_YVU420 v4l2_fourcc('Y','V','1','2') /* 12 YVU 4:2:0 */ #define V4L2_PIX_FMT_YUYV v4l2_fourcc('Y','U','Y','V') /* 16 YUV 4:2:2 */ #define V4L2_PIX_FMT_UYVY v4l2_fourcc('U','Y','V','Y') /* 16 YUV 4:2:2 */ #define V4L2_PIX_FMT_YUV422P v4l2_fourcc('4','2','2','P') /* 16 YVU422 planar */ #define V4L2_PIX_FMT_YUV411P v4l2_fourcc('4','1','1','P') /* 16 YVU411 planar */ #define V4L2_PIX_FMT_Y41P v4l2_fourcc('Y','4','1','P') /* 12 YUV 4:1:1 */ #define V4L2_PIX_FMT_YUV444 v4l2_fourcc('Y','4','4','4') /* 16 xxxxyyyy uuuuvvvv */ #define V4L2_PIX_FMT_YUV555 v4l2_fourcc('Y','U','V','O') /* 16 YUV-5-5-5 */ #define V4L2_PIX_FMT_YUV565 v4l2_fourcc('Y','U','V','P') /* 16 YUV-5-6-5 */ #define V4L2_PIX_FMT_YUV32 v4l2_fourcc('Y','U','V','4') /* 32 YUV-8-8-8-8 */ /* two planes -- one Y, one Cr + Cb interleaved */ #define V4L2_PIX_FMT_NV12 v4l2_fourcc('N','V','1','2') /* 12 Y/CbCr 4:2:0 */ #define V4L2_PIX_FMT_NV21 v4l2_fourcc('N','V','2','1') /* 12 Y/CrCb 4:2:0 */ /* The following formats are not defined in the V4L2 specification */ #define V4L2_PIX_FMT_YUV410 v4l2_fourcc('Y','U','V','9') /* 9 YUV 4:1:0 */ #define V4L2_PIX_FMT_YUV420 v4l2_fourcc('Y','U','1','2') /* 12 YUV 4:2:0 */ #define V4L2_PIX_FMT_YYUV v4l2_fourcc('Y','Y','U','V') /* 16 YUV 4:2:2 */ #define V4L2_PIX_FMT_HI240 v4l2_fourcc('H','I','2','4') /* 8 8-bit color */ #define V4L2_PIX_FMT_HM12 v4l2_fourcc('H','M','1','2') /* 8 YUV 4:2:0 16x16 macroblocks */ /* see http://www.siliconimaging.com/RGB%20Bayer.htm */ #define V4L2_PIX_FMT_SBGGR8 v4l2_fourcc('B','A','8','1') /* 8 BGBG.. GRGR.. */ #define V4L2_PIX_FMT_SBGGR16 v4l2_fourcc('B','Y','R','2') /* 16 BGBG.. GRGR.. */ /* compressed formats */ #define V4L2_PIX_FMT_MJPEG v4l2_fourcc('M','J','P','G') /* Motion-JPEG */ #define V4L2_PIX_FMT_JPEG v4l2_fourcc('J','P','E','G') /* JFIF JPEG */ #define V4L2_PIX_FMT_DV v4l2_fourcc('d','v','s','d') /* 1394 */ #define V4L2_PIX_FMT_MPEG v4l2_fourcc('M','P','E','G') /* MPEG-1/2/4 */ /* Vendor-specific formats */ #define V4L2_PIX_FMT_WNVA v4l2_fourcc('W','N','V','A') /* Winnov hw compress */ #define V4L2_PIX_FMT_SN9C10X v4l2_fourcc('S','9','1','0') /* SN9C10x compression */ #define V4L2_PIX_FMT_PWC1 v4l2_fourcc('P','W','C','1') /* pwc older webcam */ #define V4L2_PIX_FMT_PWC2 v4l2_fourcc('P','W','C','2') /* pwc newer webcam */ #define V4L2_PIX_FMT_ET61X251 v4l2_fourcc('E','6','2','5') /* ET61X251 compression */ /* * F O R M A T E N U M E R A T I O N */ struct v4l2_fmtdesc { __u32 index; /* Format number */ enum v4l2_buf_type type; /* buffer type */ __u32 flags; __u8 description[32]; /* Description string */ __u32 pixelformat; /* Format fourcc */ __u32 reserved[4]; }; #define V4L2_FMT_FLAG_COMPRESSED 0x0001 #if 1 /*KEEP*/ /* Experimental Frame Size and frame rate enumeration */ /* * F R A M E S I Z E E N U M E R A T I O N */ enum v4l2_frmsizetypes { V4L2_FRMSIZE_TYPE_DISCRETE = 1, V4L2_FRMSIZE_TYPE_CONTINUOUS = 2, V4L2_FRMSIZE_TYPE_STEPWISE = 3, }; struct v4l2_frmsize_discrete { __u32 width; /* Frame width [pixel] */ __u32 height; /* Frame height [pixel] */ }; struct v4l2_frmsize_stepwise { __u32 min_width; /* Minimum frame width [pixel] */ __u32 max_width; /* Maximum frame width [pixel] */ __u32 step_width; /* Frame width step size [pixel] */ __u32 min_height; /* Minimum frame height [pixel] */ __u32 max_height; /* Maximum frame height [pixel] */ __u32 step_height; /* Frame height step size [pixel] */ }; struct v4l2_frmsizeenum { __u32 index; /* Frame size number */ __u32 pixel_format; /* Pixel format */ __u32 type; /* Frame size type the device supports. */ union { /* Frame size */ struct v4l2_frmsize_discrete discrete; struct v4l2_frmsize_stepwise stepwise; }; __u32 reserved[2]; /* Reserved space for future use */ }; /* * F R A M E R A T E E N U M E R A T I O N */ enum v4l2_frmivaltypes { V4L2_FRMIVAL_TYPE_DISCRETE = 1, V4L2_FRMIVAL_TYPE_CONTINUOUS = 2, V4L2_FRMIVAL_TYPE_STEPWISE = 3, }; struct v4l2_frmival_stepwise { struct v4l2_fract min; /* Minimum frame interval [s] */ struct v4l2_fract max; /* Maximum frame interval [s] */ struct v4l2_fract step; /* Frame interval step size [s] */ }; struct v4l2_frmivalenum { __u32 index; /* Frame format index */ __u32 pixel_format; /* Pixel format */ __u32 width; /* Frame width */ __u32 height; /* Frame height */ __u32 type; /* Frame interval type the device supports. */ union { /* Frame interval */ struct v4l2_fract discrete; struct v4l2_frmival_stepwise stepwise; }; __u32 reserved[2]; /* Reserved space for future use */ }; #endif /* * T I M E C O D E */ struct v4l2_timecode { __u32 type; __u32 flags; __u8 frames; __u8 seconds; __u8 minutes; __u8 hours; __u8 userbits[4]; }; /* Type */ #define V4L2_TC_TYPE_24FPS 1 #define V4L2_TC_TYPE_25FPS 2 #define V4L2_TC_TYPE_30FPS 3 #define V4L2_TC_TYPE_50FPS 4 #define V4L2_TC_TYPE_60FPS 5 /* Flags */ #define V4L2_TC_FLAG_DROPFRAME 0x0001 /* "drop-frame" mode */ #define V4L2_TC_FLAG_COLORFRAME 0x0002 #define V4L2_TC_USERBITS_field 0x000C #define V4L2_TC_USERBITS_USERDEFINED 0x0000 #define V4L2_TC_USERBITS_8BITCHARS 0x0008 /* The above is based on SMPTE timecodes */ struct v4l2_jpegcompression { int quality; int APPn; /* Number of APP segment to be written, * must be 0..15 */ int APP_len; /* Length of data in JPEG APPn segment */ char APP_data[60]; /* Data in the JPEG APPn segment. */ int COM_len; /* Length of data in JPEG COM segment */ char COM_data[60]; /* Data in JPEG COM segment */ __u32 jpeg_markers; /* Which markers should go into the JPEG * output. Unless you exactly know what * you do, leave them untouched. * Inluding less markers will make the * resulting code smaller, but there will * be fewer aplications which can read it. * The presence of the APP and COM marker * is influenced by APP_len and COM_len * ONLY, not by this property! */ #define V4L2_JPEG_MARKER_DHT (1<<3) /* Define Huffman Tables */ #define V4L2_JPEG_MARKER_DQT (1<<4) /* Define Quantization Tables */ #define V4L2_JPEG_MARKER_DRI (1<<5) /* Define Restart Interval */ #define V4L2_JPEG_MARKER_COM (1<<6) /* Comment segment */ #define V4L2_JPEG_MARKER_APP (1<<7) /* App segment, driver will * allways use APP0 */ }; /* * M E M O R Y - M A P P I N G B U F F E R S */ struct v4l2_requestbuffers { __u32 count; enum v4l2_buf_type type; enum v4l2_memory memory; __u32 reserved[2]; }; struct v4l2_buffer { __u32 index; enum v4l2_buf_type type; __u32 bytesused; __u32 flags; enum v4l2_field field; struct timeval timestamp; struct v4l2_timecode timecode; __u32 sequence; /* memory location */ enum v4l2_memory memory; union { __u32 offset; unsigned long userptr; } m; __u32 length; __u32 input; __u32 reserved; }; /* Flags for 'flags' field */ #define V4L2_BUF_FLAG_MAPPED 0x0001 /* Buffer is mapped (flag) */ #define V4L2_BUF_FLAG_QUEUED 0x0002 /* Buffer is queued for processing */ #define V4L2_BUF_FLAG_DONE 0x0004 /* Buffer is ready */ #define V4L2_BUF_FLAG_KEYFRAME 0x0008 /* Image is a keyframe (I-frame) */ #define V4L2_BUF_FLAG_PFRAME 0x0010 /* Image is a P-frame */ #define V4L2_BUF_FLAG_BFRAME 0x0020 /* Image is a B-frame */ #define V4L2_BUF_FLAG_TIMECODE 0x0100 /* timecode field is valid */ #define V4L2_BUF_FLAG_INPUT 0x0200 /* input field is valid */ /* * O V E R L A Y P R E V I E W */ struct v4l2_framebuffer { __u32 capability; __u32 flags; /* FIXME: in theory we should pass something like PCI device + memory * region + offset instead of some physical address */ void* base; struct v4l2_pix_format fmt; }; /* Flags for the 'capability' field. Read only */ #define V4L2_FBUF_CAP_EXTERNOVERLAY 0x0001 #define V4L2_FBUF_CAP_CHROMAKEY 0x0002 #define V4L2_FBUF_CAP_LIST_CLIPPING 0x0004 #define V4L2_FBUF_CAP_BITMAP_CLIPPING 0x0008 #define V4L2_FBUF_CAP_LOCAL_ALPHA 0x0010 #define V4L2_FBUF_CAP_GLOBAL_ALPHA 0x0020 #define V4L2_FBUF_CAP_LOCAL_INV_ALPHA 0x0040 /* Flags for the 'flags' field. */ #define V4L2_FBUF_FLAG_PRIMARY 0x0001 #define V4L2_FBUF_FLAG_OVERLAY 0x0002 #define V4L2_FBUF_FLAG_CHROMAKEY 0x0004 #define V4L2_FBUF_FLAG_LOCAL_ALPHA 0x0008 #define V4L2_FBUF_FLAG_GLOBAL_ALPHA 0x0010 #define V4L2_FBUF_FLAG_LOCAL_INV_ALPHA 0x0020 struct v4l2_clip { struct v4l2_rect c; struct v4l2_clip __user *next; }; struct v4l2_window { struct v4l2_rect w; enum v4l2_field field; __u32 chromakey; struct v4l2_clip __user *clips; __u32 clipcount; void __user *bitmap; __u8 global_alpha; }; /* * C A P T U R E P A R A M E T E R S */ struct v4l2_captureparm { __u32 capability; /* Supported modes */ __u32 capturemode; /* Current mode */ struct v4l2_fract timeperframe; /* Time per frame in .1us units */ __u32 extendedmode; /* Driver-specific extensions */ __u32 readbuffers; /* # of buffers for read */ __u32 reserved[4]; }; /* Flags for 'capability' and 'capturemode' fields */ #define V4L2_MODE_HIGHQUALITY 0x0001 /* High quality imaging mode */ #define V4L2_CAP_TIMEPERFRAME 0x1000 /* timeperframe field is supported */ struct v4l2_outputparm { __u32 capability; /* Supported modes */ __u32 outputmode; /* Current mode */ struct v4l2_fract timeperframe; /* Time per frame in seconds */ __u32 extendedmode; /* Driver-specific extensions */ __u32 writebuffers; /* # of buffers for write */ __u32 reserved[4]; }; /* * I N P U T I M A G E C R O P P I N G */ struct v4l2_cropcap { enum v4l2_buf_type type; struct v4l2_rect bounds; struct v4l2_rect defrect; struct v4l2_fract pixelaspect; }; struct v4l2_crop { enum v4l2_buf_type type; struct v4l2_rect c; }; /* * A N A L O G V I D E O S T A N D A R D */ typedef __u64 v4l2_std_id; /* one bit for each */ #define V4L2_STD_PAL_B ((v4l2_std_id)0x00000001) #define V4L2_STD_PAL_B1 ((v4l2_std_id)0x00000002) #define V4L2_STD_PAL_G ((v4l2_std_id)0x00000004) #define V4L2_STD_PAL_H ((v4l2_std_id)0x00000008) #define V4L2_STD_PAL_I ((v4l2_std_id)0x00000010) #define V4L2_STD_PAL_D ((v4l2_std_id)0x00000020) #define V4L2_STD_PAL_D1 ((v4l2_std_id)0x00000040) #define V4L2_STD_PAL_K ((v4l2_std_id)0x00000080) #define V4L2_STD_PAL_M ((v4l2_std_id)0x00000100) #define V4L2_STD_PAL_N ((v4l2_std_id)0x00000200) #define V4L2_STD_PAL_Nc ((v4l2_std_id)0x00000400) #define V4L2_STD_PAL_60 ((v4l2_std_id)0x00000800) #define V4L2_STD_NTSC_M ((v4l2_std_id)0x00001000) #define V4L2_STD_NTSC_M_JP ((v4l2_std_id)0x00002000) #define V4L2_STD_NTSC_443 ((v4l2_std_id)0x00004000) #define V4L2_STD_NTSC_M_KR ((v4l2_std_id)0x00008000) #define V4L2_STD_SECAM_B ((v4l2_std_id)0x00010000) #define V4L2_STD_SECAM_D ((v4l2_std_id)0x00020000) #define V4L2_STD_SECAM_G ((v4l2_std_id)0x00040000) #define V4L2_STD_SECAM_H ((v4l2_std_id)0x00080000) #define V4L2_STD_SECAM_K ((v4l2_std_id)0x00100000) #define V4L2_STD_SECAM_K1 ((v4l2_std_id)0x00200000) #define V4L2_STD_SECAM_L ((v4l2_std_id)0x00400000) #define V4L2_STD_SECAM_LC ((v4l2_std_id)0x00800000) /* ATSC/HDTV */ #define V4L2_STD_ATSC_8_VSB ((v4l2_std_id)0x01000000) #define V4L2_STD_ATSC_16_VSB ((v4l2_std_id)0x02000000) /* FIXME: Although std_id is 64 bits, there is an issue on PPC32 architecture that makes switch(__u64) to break. So, there's a hack on v4l2-common.c rounding this value to 32 bits. As, currently, the max value is for V4L2_STD_ATSC_16_VSB (30 bits wide), it should work fine. However, if needed to add more than two standards, v4l2-common.c should be fixed. */ /* some merged standards */ #define V4L2_STD_MN (V4L2_STD_PAL_M|V4L2_STD_PAL_N|V4L2_STD_PAL_Nc|V4L2_STD_NTSC) #define V4L2_STD_B (V4L2_STD_PAL_B|V4L2_STD_PAL_B1|V4L2_STD_SECAM_B) #define V4L2_STD_GH (V4L2_STD_PAL_G|V4L2_STD_PAL_H|V4L2_STD_SECAM_G|V4L2_STD_SECAM_H) #define V4L2_STD_DK (V4L2_STD_PAL_DK|V4L2_STD_SECAM_DK) /* some common needed stuff */ #define V4L2_STD_PAL_BG (V4L2_STD_PAL_B |\ V4L2_STD_PAL_B1 |\ V4L2_STD_PAL_G) #define V4L2_STD_PAL_DK (V4L2_STD_PAL_D |\ V4L2_STD_PAL_D1 |\ V4L2_STD_PAL_K) #define V4L2_STD_PAL (V4L2_STD_PAL_BG |\ V4L2_STD_PAL_DK |\ V4L2_STD_PAL_H |\ V4L2_STD_PAL_I) #define V4L2_STD_NTSC (V4L2_STD_NTSC_M |\ V4L2_STD_NTSC_M_JP |\ V4L2_STD_NTSC_M_KR) #define V4L2_STD_SECAM_DK (V4L2_STD_SECAM_D |\ V4L2_STD_SECAM_K |\ V4L2_STD_SECAM_K1) #define V4L2_STD_SECAM (V4L2_STD_SECAM_B |\ V4L2_STD_SECAM_G |\ V4L2_STD_SECAM_H |\ V4L2_STD_SECAM_DK |\ V4L2_STD_SECAM_L |\ V4L2_STD_SECAM_LC) #define V4L2_STD_525_60 (V4L2_STD_PAL_M |\ V4L2_STD_PAL_60 |\ V4L2_STD_NTSC |\ V4L2_STD_NTSC_443) #define V4L2_STD_625_50 (V4L2_STD_PAL |\ V4L2_STD_PAL_N |\ V4L2_STD_PAL_Nc |\ V4L2_STD_SECAM) #define V4L2_STD_ATSC (V4L2_STD_ATSC_8_VSB |\ V4L2_STD_ATSC_16_VSB) #define V4L2_STD_UNKNOWN 0 #define V4L2_STD_ALL (V4L2_STD_525_60 |\ V4L2_STD_625_50) struct v4l2_standard { __u32 index; v4l2_std_id id; __u8 name[24]; struct v4l2_fract frameperiod; /* Frames, not fields */ __u32 framelines; __u32 reserved[4]; }; /* * V I D E O I N P U T S */ struct v4l2_input { __u32 index; /* Which input */ __u8 name[32]; /* Label */ __u32 type; /* Type of input */ __u32 audioset; /* Associated audios (bitfield) */ __u32 tuner; /* Associated tuner */ v4l2_std_id std; __u32 status; __u32 reserved[4]; }; /* Values for the 'type' field */ #define V4L2_INPUT_TYPE_TUNER 1 #define V4L2_INPUT_TYPE_CAMERA 2 /* field 'status' - general */ #define V4L2_IN_ST_NO_POWER 0x00000001 /* Attached device is off */ #define V4L2_IN_ST_NO_SIGNAL 0x00000002 #define V4L2_IN_ST_NO_COLOR 0x00000004 /* field 'status' - analog */ #define V4L2_IN_ST_NO_H_LOCK 0x00000100 /* No horizontal sync lock */ #define V4L2_IN_ST_COLOR_KILL 0x00000200 /* Color killer is active */ /* field 'status' - digital */ #define V4L2_IN_ST_NO_SYNC 0x00010000 /* No synchronization lock */ #define V4L2_IN_ST_NO_EQU 0x00020000 /* No equalizer lock */ #define V4L2_IN_ST_NO_CARRIER 0x00040000 /* Carrier recovery failed */ /* field 'status' - VCR and set-top box */ #define V4L2_IN_ST_MACROVISION 0x01000000 /* Macrovision detected */ #define V4L2_IN_ST_NO_ACCESS 0x02000000 /* Conditional access denied */ #define V4L2_IN_ST_VTR 0x04000000 /* VTR time constant */ /* * V I D E O O U T P U T S */ struct v4l2_output { __u32 index; /* Which output */ __u8 name[32]; /* Label */ __u32 type; /* Type of output */ __u32 audioset; /* Associated audios (bitfield) */ __u32 modulator; /* Associated modulator */ v4l2_std_id std; __u32 reserved[4]; }; /* Values for the 'type' field */ #define V4L2_OUTPUT_TYPE_MODULATOR 1 #define V4L2_OUTPUT_TYPE_ANALOG 2 #define V4L2_OUTPUT_TYPE_ANALOGVGAOVERLAY 3 /* * C O N T R O L S */ struct v4l2_control { __u32 id; __s32 value; }; struct v4l2_ext_control { __u32 id; __u32 reserved2[2]; union { __s32 value; __s64 value64; void *reserved; }; } __attribute__ ((packed)); struct v4l2_ext_controls { __u32 ctrl_class; __u32 count; __u32 error_idx; __u32 reserved[2]; struct v4l2_ext_control *controls; }; /* Values for ctrl_class field */ #define V4L2_CTRL_CLASS_USER 0x00980000 /* Old-style 'user' controls */ #define V4L2_CTRL_CLASS_MPEG 0x00990000 /* MPEG-compression controls */ #define V4L2_CTRL_CLASS_CAMERA 0x009a0000 /* Camera class controls */ #define V4L2_CTRL_ID_MASK (0x0fffffff) #define V4L2_CTRL_ID2CLASS(id) ((id) & 0x0fff0000UL) #define V4L2_CTRL_DRIVER_PRIV(id) (((id) & 0xffff) >= 0x1000) /* Used in the VIDIOC_QUERYCTRL ioctl for querying controls */ struct v4l2_queryctrl { __u32 id; enum v4l2_ctrl_type type; __u8 name[32]; /* Whatever */ __s32 minimum; /* Note signedness */ __s32 maximum; __s32 step; __s32 default_value; __u32 flags; __u32 reserved[2]; }; /* Used in the VIDIOC_QUERYMENU ioctl for querying menu items */ struct v4l2_querymenu { __u32 id; __u32 index; __u8 name[32]; /* Whatever */ __u32 reserved; }; /* Control flags */ #define V4L2_CTRL_FLAG_DISABLED 0x0001 #define V4L2_CTRL_FLAG_GRABBED 0x0002 #define V4L2_CTRL_FLAG_READ_ONLY 0x0004 #define V4L2_CTRL_FLAG_UPDATE 0x0008 #define V4L2_CTRL_FLAG_INACTIVE 0x0010 #define V4L2_CTRL_FLAG_SLIDER 0x0020 /* Query flag, to be ORed with the control ID */ #define V4L2_CTRL_FLAG_NEXT_CTRL 0x80000000 /* User-class control IDs defined by V4L2 */ #define V4L2_CID_BASE (V4L2_CTRL_CLASS_USER | 0x900) #define V4L2_CID_USER_BASE V4L2_CID_BASE /* IDs reserved for driver specific controls */ #define V4L2_CID_PRIVATE_BASE 0x08000000 #define V4L2_CID_USER_CLASS (V4L2_CTRL_CLASS_USER | 1) #define V4L2_CID_BRIGHTNESS (V4L2_CID_BASE+0) #define V4L2_CID_CONTRAST (V4L2_CID_BASE+1) #define V4L2_CID_SATURATION (V4L2_CID_BASE+2) #define V4L2_CID_HUE (V4L2_CID_BASE+3) #define V4L2_CID_AUDIO_VOLUME (V4L2_CID_BASE+5) #define V4L2_CID_AUDIO_BALANCE (V4L2_CID_BASE+6) #define V4L2_CID_AUDIO_BASS (V4L2_CID_BASE+7) #define V4L2_CID_AUDIO_TREBLE (V4L2_CID_BASE+8) #define V4L2_CID_AUDIO_MUTE (V4L2_CID_BASE+9) #define V4L2_CID_AUDIO_LOUDNESS (V4L2_CID_BASE+10) #define V4L2_CID_BLACK_LEVEL (V4L2_CID_BASE+11) /* Deprecated */ #define V4L2_CID_AUTO_WHITE_BALANCE (V4L2_CID_BASE+12) #define V4L2_CID_DO_WHITE_BALANCE (V4L2_CID_BASE+13) #define V4L2_CID_RED_BALANCE (V4L2_CID_BASE+14) #define V4L2_CID_BLUE_BALANCE (V4L2_CID_BASE+15) #define V4L2_CID_GAMMA (V4L2_CID_BASE+16) #define V4L2_CID_WHITENESS (V4L2_CID_GAMMA) /* Deprecated */ #define V4L2_CID_EXPOSURE (V4L2_CID_BASE+17) #define V4L2_CID_AUTOGAIN (V4L2_CID_BASE+18) #define V4L2_CID_GAIN (V4L2_CID_BASE+19) #define V4L2_CID_HFLIP (V4L2_CID_BASE+20) #define V4L2_CID_VFLIP (V4L2_CID_BASE+21) /* Deprecated, use V4L2_CID_PAN_RESET and V4L2_CID_TILT_RESET */ #define V4L2_CID_HCENTER_DEPRECATED (V4L2_CID_BASE+22) #define V4L2_CID_VCENTER_DEPRECATED (V4L2_CID_BASE+23) #define V4L2_CID_POWER_LINE_FREQUENCY (V4L2_CID_BASE+24) enum v4l2_power_line_frequency { V4L2_CID_POWER_LINE_FREQUENCY_DISABLED = 0, V4L2_CID_POWER_LINE_FREQUENCY_50HZ = 1, V4L2_CID_POWER_LINE_FREQUENCY_60HZ = 2, }; #define V4L2_CID_HUE_AUTO (V4L2_CID_BASE+25) #define V4L2_CID_WHITE_BALANCE_TEMPERATURE (V4L2_CID_BASE+26) #define V4L2_CID_SHARPNESS (V4L2_CID_BASE+27) #define V4L2_CID_BACKLIGHT_COMPENSATION (V4L2_CID_BASE+28) #define V4L2_CID_LASTP1 (V4L2_CID_BASE+29) /* last CID + 1 */ /* MPEG-class control IDs defined by V4L2 */ #define V4L2_CID_MPEG_BASE (V4L2_CTRL_CLASS_MPEG | 0x900) #define V4L2_CID_MPEG_CLASS (V4L2_CTRL_CLASS_MPEG | 1) /* MPEG streams */ #define V4L2_CID_MPEG_STREAM_TYPE (V4L2_CID_MPEG_BASE+0) enum v4l2_mpeg_stream_type { V4L2_MPEG_STREAM_TYPE_MPEG2_PS = 0, /* MPEG-2 program stream */ V4L2_MPEG_STREAM_TYPE_MPEG2_TS = 1, /* MPEG-2 transport stream */ V4L2_MPEG_STREAM_TYPE_MPEG1_SS = 2, /* MPEG-1 system stream */ V4L2_MPEG_STREAM_TYPE_MPEG2_DVD = 3, /* MPEG-2 DVD-compatible stream */ V4L2_MPEG_STREAM_TYPE_MPEG1_VCD = 4, /* MPEG-1 VCD-compatible stream */ V4L2_MPEG_STREAM_TYPE_MPEG2_SVCD = 5, /* MPEG-2 SVCD-compatible stream */ }; #define V4L2_CID_MPEG_STREAM_PID_PMT (V4L2_CID_MPEG_BASE+1) #define V4L2_CID_MPEG_STREAM_PID_AUDIO (V4L2_CID_MPEG_BASE+2) #define V4L2_CID_MPEG_STREAM_PID_VIDEO (V4L2_CID_MPEG_BASE+3) #define V4L2_CID_MPEG_STREAM_PID_PCR (V4L2_CID_MPEG_BASE+4) #define V4L2_CID_MPEG_STREAM_PES_ID_AUDIO (V4L2_CID_MPEG_BASE+5) #define V4L2_CID_MPEG_STREAM_PES_ID_VIDEO (V4L2_CID_MPEG_BASE+6) #define V4L2_CID_MPEG_STREAM_VBI_FMT (V4L2_CID_MPEG_BASE+7) enum v4l2_mpeg_stream_vbi_fmt { V4L2_MPEG_STREAM_VBI_FMT_NONE = 0, /* No VBI in the MPEG stream */ V4L2_MPEG_STREAM_VBI_FMT_IVTV = 1, /* VBI in private packets, IVTV format */ }; /* MPEG audio */ #define V4L2_CID_MPEG_AUDIO_SAMPLING_FREQ (V4L2_CID_MPEG_BASE+100) enum v4l2_mpeg_audio_sampling_freq { V4L2_MPEG_AUDIO_SAMPLING_FREQ_44100 = 0, V4L2_MPEG_AUDIO_SAMPLING_FREQ_48000 = 1, V4L2_MPEG_AUDIO_SAMPLING_FREQ_32000 = 2, }; #define V4L2_CID_MPEG_AUDIO_ENCODING (V4L2_CID_MPEG_BASE+101) enum v4l2_mpeg_audio_encoding { V4L2_MPEG_AUDIO_ENCODING_LAYER_1 = 0, V4L2_MPEG_AUDIO_ENCODING_LAYER_2 = 1, V4L2_MPEG_AUDIO_ENCODING_LAYER_3 = 2, }; #define V4L2_CID_MPEG_AUDIO_L1_BITRATE (V4L2_CID_MPEG_BASE+102) enum v4l2_mpeg_audio_l1_bitrate { V4L2_MPEG_AUDIO_L1_BITRATE_32K = 0, V4L2_MPEG_AUDIO_L1_BITRATE_64K = 1, V4L2_MPEG_AUDIO_L1_BITRATE_96K = 2, V4L2_MPEG_AUDIO_L1_BITRATE_128K = 3, V4L2_MPEG_AUDIO_L1_BITRATE_160K = 4, V4L2_MPEG_AUDIO_L1_BITRATE_192K = 5, V4L2_MPEG_AUDIO_L1_BITRATE_224K = 6, V4L2_MPEG_AUDIO_L1_BITRATE_256K = 7, V4L2_MPEG_AUDIO_L1_BITRATE_288K = 8, V4L2_MPEG_AUDIO_L1_BITRATE_320K = 9, V4L2_MPEG_AUDIO_L1_BITRATE_352K = 10, V4L2_MPEG_AUDIO_L1_BITRATE_384K = 11, V4L2_MPEG_AUDIO_L1_BITRATE_416K = 12, V4L2_MPEG_AUDIO_L1_BITRATE_448K = 13, }; #define V4L2_CID_MPEG_AUDIO_L2_BITRATE (V4L2_CID_MPEG_BASE+103) enum v4l2_mpeg_audio_l2_bitrate { V4L2_MPEG_AUDIO_L2_BITRATE_32K = 0, V4L2_MPEG_AUDIO_L2_BITRATE_48K = 1, V4L2_MPEG_AUDIO_L2_BITRATE_56K = 2, V4L2_MPEG_AUDIO_L2_BITRATE_64K = 3, V4L2_MPEG_AUDIO_L2_BITRATE_80K = 4, V4L2_MPEG_AUDIO_L2_BITRATE_96K = 5, V4L2_MPEG_AUDIO_L2_BITRATE_112K = 6, V4L2_MPEG_AUDIO_L2_BITRATE_128K = 7, V4L2_MPEG_AUDIO_L2_BITRATE_160K = 8, V4L2_MPEG_AUDIO_L2_BITRATE_192K = 9, V4L2_MPEG_AUDIO_L2_BITRATE_224K = 10, V4L2_MPEG_AUDIO_L2_BITRATE_256K = 11, V4L2_MPEG_AUDIO_L2_BITRATE_320K = 12, V4L2_MPEG_AUDIO_L2_BITRATE_384K = 13, }; #define V4L2_CID_MPEG_AUDIO_L3_BITRATE (V4L2_CID_MPEG_BASE+104) enum v4l2_mpeg_audio_l3_bitrate { V4L2_MPEG_AUDIO_L3_BITRATE_32K = 0, V4L2_MPEG_AUDIO_L3_BITRATE_40K = 1, V4L2_MPEG_AUDIO_L3_BITRATE_48K = 2, V4L2_MPEG_AUDIO_L3_BITRATE_56K = 3, V4L2_MPEG_AUDIO_L3_BITRATE_64K = 4, V4L2_MPEG_AUDIO_L3_BITRATE_80K = 5, V4L2_MPEG_AUDIO_L3_BITRATE_96K = 6, V4L2_MPEG_AUDIO_L3_BITRATE_112K = 7, V4L2_MPEG_AUDIO_L3_BITRATE_128K = 8, V4L2_MPEG_AUDIO_L3_BITRATE_160K = 9, V4L2_MPEG_AUDIO_L3_BITRATE_192K = 10, V4L2_MPEG_AUDIO_L3_BITRATE_224K = 11, V4L2_MPEG_AUDIO_L3_BITRATE_256K = 12, V4L2_MPEG_AUDIO_L3_BITRATE_320K = 13, }; #define V4L2_CID_MPEG_AUDIO_MODE (V4L2_CID_MPEG_BASE+105) enum v4l2_mpeg_audio_mode { V4L2_MPEG_AUDIO_MODE_STEREO = 0, V4L2_MPEG_AUDIO_MODE_JOINT_STEREO = 1, V4L2_MPEG_AUDIO_MODE_DUAL = 2, V4L2_MPEG_AUDIO_MODE_MONO = 3, }; #define V4L2_CID_MPEG_AUDIO_MODE_EXTENSION (V4L2_CID_MPEG_BASE+106) enum v4l2_mpeg_audio_mode_extension { V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_4 = 0, V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_8 = 1, V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_12 = 2, V4L2_MPEG_AUDIO_MODE_EXTENSION_BOUND_16 = 3, }; #define V4L2_CID_MPEG_AUDIO_EMPHASIS (V4L2_CID_MPEG_BASE+107) enum v4l2_mpeg_audio_emphasis { V4L2_MPEG_AUDIO_EMPHASIS_NONE = 0, V4L2_MPEG_AUDIO_EMPHASIS_50_DIV_15_uS = 1, V4L2_MPEG_AUDIO_EMPHASIS_CCITT_J17 = 2, }; #define V4L2_CID_MPEG_AUDIO_CRC (V4L2_CID_MPEG_BASE+108) enum v4l2_mpeg_audio_crc { V4L2_MPEG_AUDIO_CRC_NONE = 0, V4L2_MPEG_AUDIO_CRC_CRC16 = 1, }; #define V4L2_CID_MPEG_AUDIO_MUTE (V4L2_CID_MPEG_BASE+109) /* MPEG video */ #define V4L2_CID_MPEG_VIDEO_ENCODING (V4L2_CID_MPEG_BASE+200) enum v4l2_mpeg_video_encoding { V4L2_MPEG_VIDEO_ENCODING_MPEG_1 = 0, V4L2_MPEG_VIDEO_ENCODING_MPEG_2 = 1, }; #define V4L2_CID_MPEG_VIDEO_ASPECT (V4L2_CID_MPEG_BASE+201) enum v4l2_mpeg_video_aspect { V4L2_MPEG_VIDEO_ASPECT_1x1 = 0, V4L2_MPEG_VIDEO_ASPECT_4x3 = 1, V4L2_MPEG_VIDEO_ASPECT_16x9 = 2, V4L2_MPEG_VIDEO_ASPECT_221x100 = 3, }; #define V4L2_CID_MPEG_VIDEO_B_FRAMES (V4L2_CID_MPEG_BASE+202) #define V4L2_CID_MPEG_VIDEO_GOP_SIZE (V4L2_CID_MPEG_BASE+203) #define V4L2_CID_MPEG_VIDEO_GOP_CLOSURE (V4L2_CID_MPEG_BASE+204) #define V4L2_CID_MPEG_VIDEO_PULLDOWN (V4L2_CID_MPEG_BASE+205) #define V4L2_CID_MPEG_VIDEO_BITRATE_MODE (V4L2_CID_MPEG_BASE+206) enum v4l2_mpeg_video_bitrate_mode { V4L2_MPEG_VIDEO_BITRATE_MODE_VBR = 0, V4L2_MPEG_VIDEO_BITRATE_MODE_CBR = 1, }; #define V4L2_CID_MPEG_VIDEO_BITRATE (V4L2_CID_MPEG_BASE+207) #define V4L2_CID_MPEG_VIDEO_BITRATE_PEAK (V4L2_CID_MPEG_BASE+208) #define V4L2_CID_MPEG_VIDEO_TEMPORAL_DECIMATION (V4L2_CID_MPEG_BASE+209) #define V4L2_CID_MPEG_VIDEO_MUTE (V4L2_CID_MPEG_BASE+210) #define V4L2_CID_MPEG_VIDEO_MUTE_YUV (V4L2_CID_MPEG_BASE+211) /* MPEG-class control IDs specific to the CX2584x driver as defined by V4L2 */ #define V4L2_CID_MPEG_CX2341X_BASE (V4L2_CTRL_CLASS_MPEG | 0x1000) #define V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE (V4L2_CID_MPEG_CX2341X_BASE+0) enum v4l2_mpeg_cx2341x_video_spatial_filter_mode { V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_MANUAL = 0, V4L2_MPEG_CX2341X_VIDEO_SPATIAL_FILTER_MODE_AUTO = 1, }; #define V4L2_CID_MPEG_CX2341X_VIDEO_SPATIAL_FILTER (V4L2_CID_MPEG_CX2341X_BASE+1) #define V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE (V4L2_CID_MPEG_CX2341X_BASE+2) enum v4l2_mpeg_cx2341x_video_luma_spatial_filter_type { V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_OFF = 0, V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_HOR = 1, V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_1D_VERT = 2, V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_HV_SEPARABLE = 3, V4L2_MPEG_CX2341X_VIDEO_LUMA_SPATIAL_FILTER_TYPE_2D_SYM_NON_SEPARABLE = 4, }; #define V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE (V4L2_CID_MPEG_CX2341X_BASE+3) enum v4l2_mpeg_cx2341x_video_chroma_spatial_filter_type { V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_OFF = 0, V4L2_MPEG_CX2341X_VIDEO_CHROMA_SPATIAL_FILTER_TYPE_1D_HOR = 1, }; #define V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE (V4L2_CID_MPEG_CX2341X_BASE+4) enum v4l2_mpeg_cx2341x_video_temporal_filter_mode { V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_MANUAL = 0, V4L2_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER_MODE_AUTO = 1, }; #define V4L2_CID_MPEG_CX2341X_VIDEO_TEMPORAL_FILTER (V4L2_CID_MPEG_CX2341X_BASE+5) #define V4L2_CID_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE (V4L2_CID_MPEG_CX2341X_BASE+6) enum v4l2_mpeg_cx2341x_video_median_filter_type { V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_OFF = 0, V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR = 1, V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_VERT = 2, V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_HOR_VERT = 3, V4L2_MPEG_CX2341X_VIDEO_MEDIAN_FILTER_TYPE_DIAG = 4, }; #define V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_BOTTOM (V4L2_CID_MPEG_CX2341X_BASE+7) #define V4L2_CID_MPEG_CX2341X_VIDEO_LUMA_MEDIAN_FILTER_TOP (V4L2_CID_MPEG_CX2341X_BASE+8) #define V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_BOTTOM (V4L2_CID_MPEG_CX2341X_BASE+9) #define V4L2_CID_MPEG_CX2341X_VIDEO_CHROMA_MEDIAN_FILTER_TOP (V4L2_CID_MPEG_CX2341X_BASE+10) #define V4L2_CID_MPEG_CX2341X_STREAM_INSERT_NAV_PACKETS (V4L2_CID_MPEG_CX2341X_BASE+11) /* Camera class control IDs */ #define V4L2_CID_CAMERA_CLASS_BASE (V4L2_CTRL_CLASS_CAMERA | 0x900) #define V4L2_CID_CAMERA_CLASS (V4L2_CTRL_CLASS_CAMERA | 1) #define V4L2_CID_EXPOSURE_AUTO (V4L2_CID_CAMERA_CLASS_BASE+1) enum v4l2_exposure_auto_type { V4L2_EXPOSURE_AUTO = 0, V4L2_EXPOSURE_MANUAL = 1, V4L2_EXPOSURE_SHUTTER_PRIORITY = 2, V4L2_EXPOSURE_APERTURE_PRIORITY = 3 }; #define V4L2_CID_EXPOSURE_ABSOLUTE (V4L2_CID_CAMERA_CLASS_BASE+2) #define V4L2_CID_EXPOSURE_AUTO_PRIORITY (V4L2_CID_CAMERA_CLASS_BASE+3) #define V4L2_CID_PAN_RELATIVE (V4L2_CID_CAMERA_CLASS_BASE+4) #define V4L2_CID_TILT_RELATIVE (V4L2_CID_CAMERA_CLASS_BASE+5) #define V4L2_CID_PAN_RESET (V4L2_CID_CAMERA_CLASS_BASE+6) #define V4L2_CID_TILT_RESET (V4L2_CID_CAMERA_CLASS_BASE+7) #define V4L2_CID_PAN_ABSOLUTE (V4L2_CID_CAMERA_CLASS_BASE+8) #define V4L2_CID_TILT_ABSOLUTE (V4L2_CID_CAMERA_CLASS_BASE+9) #define V4L2_CID_FOCUS_ABSOLUTE (V4L2_CID_CAMERA_CLASS_BASE+10) #define V4L2_CID_FOCUS_RELATIVE (V4L2_CID_CAMERA_CLASS_BASE+11) #define V4L2_CID_FOCUS_AUTO (V4L2_CID_CAMERA_CLASS_BASE+12) /* * T U N I N G */ struct v4l2_tuner { __u32 index; __u8 name[32]; enum v4l2_tuner_type type; __u32 capability; __u32 rangelow; __u32 rangehigh; __u32 rxsubchans; __u32 audmode; __s32 signal; __s32 afc; __u32 reserved[4]; }; struct v4l2_modulator { __u32 index; __u8 name[32]; __u32 capability; __u32 rangelow; __u32 rangehigh; __u32 txsubchans; __u32 reserved[4]; }; /* Flags for the 'capability' field */ #define V4L2_TUNER_CAP_LOW 0x0001 #define V4L2_TUNER_CAP_NORM 0x0002 #define V4L2_TUNER_CAP_STEREO 0x0010 #define V4L2_TUNER_CAP_LANG2 0x0020 #define V4L2_TUNER_CAP_SAP 0x0020 #define V4L2_TUNER_CAP_LANG1 0x0040 /* Flags for the 'rxsubchans' field */ #define V4L2_TUNER_SUB_MONO 0x0001 #define V4L2_TUNER_SUB_STEREO 0x0002 #define V4L2_TUNER_SUB_LANG2 0x0004 #define V4L2_TUNER_SUB_SAP 0x0004 #define V4L2_TUNER_SUB_LANG1 0x0008 /* Values for the 'audmode' field */ #define V4L2_TUNER_MODE_MONO 0x0000 #define V4L2_TUNER_MODE_STEREO 0x0001 #define V4L2_TUNER_MODE_LANG2 0x0002 #define V4L2_TUNER_MODE_SAP 0x0002 #define V4L2_TUNER_MODE_LANG1 0x0003 #define V4L2_TUNER_MODE_LANG1_LANG2 0x0004 struct v4l2_frequency { __u32 tuner; enum v4l2_tuner_type type; __u32 frequency; __u32 reserved[8]; }; /* * A U D I O */ struct v4l2_audio { __u32 index; __u8 name[32]; __u32 capability; __u32 mode; __u32 reserved[2]; }; /* Flags for the 'capability' field */ #define V4L2_AUDCAP_STEREO 0x00001 #define V4L2_AUDCAP_AVL 0x00002 /* Flags for the 'mode' field */ #define V4L2_AUDMODE_AVL 0x00001 struct v4l2_audioout { __u32 index; __u8 name[32]; __u32 capability; __u32 mode; __u32 reserved[2]; }; /* * M P E G S E R V I C E S * * NOTE: EXPERIMENTAL API */ #if 1 /*KEEP*/ #define V4L2_ENC_IDX_FRAME_I (0) #define V4L2_ENC_IDX_FRAME_P (1) #define V4L2_ENC_IDX_FRAME_B (2) #define V4L2_ENC_IDX_FRAME_MASK (0xf) struct v4l2_enc_idx_entry { __u64 offset; __u64 pts; __u32 length; __u32 flags; __u32 reserved[2]; }; #define V4L2_ENC_IDX_ENTRIES (64) struct v4l2_enc_idx { __u32 entries; __u32 entries_cap; __u32 reserved[4]; struct v4l2_enc_idx_entry entry[V4L2_ENC_IDX_ENTRIES]; }; #define V4L2_ENC_CMD_START (0) #define V4L2_ENC_CMD_STOP (1) #define V4L2_ENC_CMD_PAUSE (2) #define V4L2_ENC_CMD_RESUME (3) /* Flags for V4L2_ENC_CMD_STOP */ #define V4L2_ENC_CMD_STOP_AT_GOP_END (1 << 0) struct v4l2_encoder_cmd { __u32 cmd; __u32 flags; union { struct { __u32 data[8]; } raw; }; }; #endif /* * D A T A S E R V I C E S ( V B I ) * * Data services API by Michael Schimek */ /* Raw VBI */ struct v4l2_vbi_format { __u32 sampling_rate; /* in 1 Hz */ __u32 offset; __u32 samples_per_line; __u32 sample_format; /* V4L2_PIX_FMT_* */ __s32 start[2]; __u32 count[2]; __u32 flags; /* V4L2_VBI_* */ __u32 reserved[2]; /* must be zero */ }; /* VBI flags */ #define V4L2_VBI_UNSYNC (1<< 0) #define V4L2_VBI_INTERLACED (1<< 1) /* Sliced VBI * * This implements is a proposal V4L2 API to allow SLICED VBI * required for some hardware encoders. It should change without * notice in the definitive implementation. */ struct v4l2_sliced_vbi_format { __u16 service_set; /* service_lines[0][...] specifies lines 0-23 (1-23 used) of the first field service_lines[1][...] specifies lines 0-23 (1-23 used) of the second field (equals frame lines 313-336 for 625 line video standards, 263-286 for 525 line standards) */ __u16 service_lines[2][24]; __u32 io_size; __u32 reserved[2]; /* must be zero */ }; /* Teletext World System Teletext (WST), defined on ITU-R BT.653-2 */ #define V4L2_SLICED_TELETEXT_B (0x0001) /* Video Program System, defined on ETS 300 231*/ #define V4L2_SLICED_VPS (0x0400) /* Closed Caption, defined on EIA-608 */ #define V4L2_SLICED_CAPTION_525 (0x1000) /* Wide Screen System, defined on ITU-R BT1119.1 */ #define V4L2_SLICED_WSS_625 (0x4000) #define V4L2_SLICED_VBI_525 (V4L2_SLICED_CAPTION_525) #define V4L2_SLICED_VBI_625 (V4L2_SLICED_TELETEXT_B | V4L2_SLICED_VPS | V4L2_SLICED_WSS_625) struct v4l2_sliced_vbi_cap { __u16 service_set; /* service_lines[0][...] specifies lines 0-23 (1-23 used) of the first field service_lines[1][...] specifies lines 0-23 (1-23 used) of the second field (equals frame lines 313-336 for 625 line video standards, 263-286 for 525 line standards) */ __u16 service_lines[2][24]; enum v4l2_buf_type type; __u32 reserved[3]; /* must be 0 */ }; struct v4l2_sliced_vbi_data { __u32 id; __u32 field; /* 0: first field, 1: second field */ __u32 line; /* 1-23 */ __u32 reserved; /* must be 0 */ __u8 data[48]; }; /* * A G G R E G A T E S T R U C T U R E S */ /* Stream data format */ struct v4l2_format { enum v4l2_buf_type type; union { struct v4l2_pix_format pix; // V4L2_BUF_TYPE_VIDEO_CAPTURE struct v4l2_window win; // V4L2_BUF_TYPE_VIDEO_OVERLAY struct v4l2_vbi_format vbi; // V4L2_BUF_TYPE_VBI_CAPTURE struct v4l2_sliced_vbi_format sliced; // V4L2_BUF_TYPE_SLICED_VBI_CAPTURE __u8 raw_data[200]; // user-defined } fmt; }; /* Stream type-dependent parameters */ struct v4l2_streamparm { enum v4l2_buf_type type; union { struct v4l2_captureparm capture; struct v4l2_outputparm output; __u8 raw_data[200]; /* user-defined */ } parm; }; /* * A D V A N C E D D E B U G G I N G * * NOTE: EXPERIMENTAL API */ /* VIDIOC_DBG_G_REGISTER and VIDIOC_DBG_S_REGISTER */ #define V4L2_CHIP_MATCH_HOST 0 /* Match against chip ID on host (0 for the host) */ #define V4L2_CHIP_MATCH_I2C_DRIVER 1 /* Match against I2C driver ID */ #define V4L2_CHIP_MATCH_I2C_ADDR 2 /* Match against I2C 7-bit address */ struct v4l2_register { __u32 match_type; /* Match type */ __u32 match_chip; /* Match this chip, meaning determined by match_type */ __u64 reg; __u64 val; }; /* VIDIOC_G_CHIP_IDENT */ struct v4l2_chip_ident { __u32 match_type; /* Match type */ __u32 match_chip; /* Match this chip, meaning determined by match_type */ __u32 ident; /* chip identifier as specified in <media/v4l2-chip-ident.h> */ __u32 revision; /* chip revision, chip specific */ }; /* * I O C T L C O D E S F O R V I D E O D E V I C E S * */ #define VIDIOC_QUERYCAP _IOR ('V', 0, struct v4l2_capability) #define VIDIOC_RESERVED _IO ('V', 1) #define VIDIOC_ENUM_FMT _IOWR ('V', 2, struct