pencv自带的VideoCapture()函数定义摄像头对象，其参数0表示第一个摄像头，一般就是笔记本的内建摄像头。 cap = cv2.VideoCapture("../test.avi") 逐帧显示实现视频播放 在while循环中，利用视频对象的read()函数读取视频的某帧，并显示
class VideoCapture(builtins.object)
| Methods defined here:
|
| __init__(self, /, *args, **kwargs)
| Initialize self. See help(type(self)) for accurate signature.
|
| __new__(*args, **kwargs) from builtins.type
| Create and return a new object. See help(type) for accurate signature.
|
| __repr__(self, /)
| Return repr(self).
|
| get(...)
| get(propId) -> retval
| . @brief Returns the specified VideoCapture property
| .
| . @param propId Property identifier from cv::VideoCaptureProperties (eg. cv::CAP_PROP_POS_MSEC, cv::CAP_PROP_POS_FRAMES, ...)
| . or one from @ref videoio_flags_others
| . @return Value for the specified property. Value 0 is returned when querying a property that is
| . not supported by the backend used by the VideoCapture instance.
| .
| . @note Reading / writing properties involves many layers. Some unexpected result might happens
| . along this chain.
| . @code {.txt}
| . `VideoCapture -> API Backend -> Operating System -> Device Driver -> Device Hardware`
| . @endcode
| . The returned value might be different from what really used by the device or it could be encoded
| . using device dependant rules (eg. steps or percentage). Effective behaviour depends from device
| . driver and API Backend
|
| grab(...)
| grab() -> retval
| . @brief Grabs the next frame from video file or capturing device.
| .
| . @return `true` (non-zero) in the case of success.
| .
| . The method/function grabs the next frame from video file or camera and returns true (non-zero) in
| . the case of success.
| .
| . The primary use of the function is in multi-camera environments, especially when the cameras do not
| . have hardware synchronization. That is, you call VideoCapture::grab() for each camera and after that
| . call the slower method VideoCapture::retrieve() to decode and get frame from each camera. This way
| . the overhead on demosaicing or motion jpeg decompression etc. is eliminated and the retrieved frames
| . from different cameras will be closer in time.
| .
| . Also, when a connected camera is multi-head (for example, a stereo camera or a Kinect device), the
| . correct way of retrieving data from it is to call VideoCapture::grab() first and then call
| . VideoCapture::retrieve() one or more times with different values of the channel parameter.
| .
| . @ref tutorial_kinect_openni
|
| isOpened(...)
| isOpened() -> retval
| . @brief Returns true if video capturing has been initialized already.
| .
| . If the previous call to VideoCapture constructor or VideoCapture::open() succeeded, the method returns
| . true.
|
| open(...)
| open(filename) -> retval
| . @brief Open video file or a capturing device or a IP video stream for video capturing
| .
| . @overload
| .
| . Parameters are same as the constructor VideoCapture(const String& filename)
| . @return `true` if the file has been successfully opened
| .
| . The method first calls VideoCapture::release to close the already opened file or camera.
|
|
|
| open(index) -> retval
| . @brief Open a camera for video capturing
| .
| . @overload
| .
| . Parameters are same as the constructor VideoCapture(int index)
| . @return `true` if the camera has been successfully opened.
| .
| . The method first calls VideoCapture::release to close the already opened file or camera.
|
|
|
| open(cameraNum, apiPreference) -> retval
| . @brief Open a camera for video capturing
| .
| . @overload
| .
| . Parameters are similar as the constructor VideoCapture(int index),except it takes an additional argument apiPreference.
| . Definitely, is same as open(int index) where `index=cameraNum + apiPreference`
| . @return `true` if the camera has been successfully opened.
|
|
|
| open(filename, apiPreference) -> retval
| . @brief Open video file or a capturing device or a IP video stream for video capturing with API Preference
| .
| . @overload
| .
| . Parameters are same as the constructor VideoCapture(const String& filename, int apiPreference)
| . @return `true` if the file has been successfully opened
| .
| . The method first calls VideoCapture::release to close the already opened file or camera.
|
| read(...)
| read([, image]) -> retval, image
| . @brief Grabs, decodes and returns the next video frame.
| .
| . @param [out] image the video frame is returned here. If no frames has been grabbed the image will be empty.
| . @return `false` if no frames has been grabbed
| .
| . The method/function combines VideoCapture::grab() and VideoCapture::retrieve() in one call. This is the
| . most convenient method for reading video files or capturing data from decode and returns the just
| . grabbed frame. If no frames has been grabbed (camera has been disconnected, or there are no more
| . frames in video file), the method returns false and the function returns empty image (with %cv::Mat, test it with Mat::empty()).
| .
| . @note In @ref videoio_c "C API", functions cvRetrieveFrame() and cv.RetrieveFrame() return image stored inside the video
| . capturing structure. It is not allowed to modify or release the image! You can copy the frame using
| . :ocvcvCloneImage and then do whatever you want with the copy.
|
| release(...)
| release() -> None
| . @brief Closes video file or capturing device.
| .
| . The method is automatically called by subsequent VideoCapture::open and by VideoCapture
| . destructor.
| .
| . The C function also deallocates memory and clears \*capture pointer.
|
| retrieve(...)
| retrieve([, image[, flag]]) -> retval, image
| . @brief Decodes and returns the grabbed video frame.
| .
| . @param [out] image the video frame is returned here. If no frames has been grabbed the image will be empty.
| . @param flag it could be a frame index or a driver specific flag
| . @return `false` if no frames has been grabbed
| .
| . The method decodes and returns the just grabbed frame. If no frames has been grabbed
| . (camera has been disconnected, or there are no more frames in video file), the method returns false
| . and the function returns an empty image (with %cv::Mat, test it with Mat::empty()).
| .
| . @sa read()
| .
| . @note In @ref videoio_c "C API", functions cvRetrieveFrame() and cv.RetrieveFrame() return image stored inside the video
| . capturing structure. It is not allowed to modify or release the image! You can copy the frame using
| . :ocvcvCloneImage and then do whatever you want with the copy.
|
| set(...)
| set(propId, value) -> retval
| . @brief Sets a property in the VideoCapture.
| .
| . @param propId Property identifier from cv::VideoCaptureProperties (eg. cv::CAP_PROP_POS_MSEC, cv::CAP_PROP_POS_FRAMES, ...)
| . or one from @ref videoio_flags_others
| . @param value Value of the property.
| . @return `true` if the property is supported by backend used by the VideoCapture instance.
| . @note Even if it returns `true` this doesn't ensure that the property
| . value has been accepted by the capture device. See note in VideoCapture::get()
