ffmpeg.c（4.3.1）源码剖析（一）-阿里云开发者社区

前言

本文对 ffmpeg.c 源码进行学习及剖析。

一、FFmpeg 源码结构图

链接：ffmpeg整体流程.jpg

下面对上述图片进行介绍：

函数背景色

函数在图中以方框的形式表现出来。不同的背景色标志了该函数不同的作用：

粉红色背景函数：FFmpeg 的 API 函数。
白色背景的函数：FFmpeg 的内部函数。
黄色背景的函数：URLProtocol 结构体中的函数，包含了读写各种协议的功能。
绿色背景的函数：AVOutputFormat 结构体中的函数，包含了读写各种封装格式的功能。
蓝色背景的函数：AVCodec 结构体中的函数，包含了编解码的功能。

区域

整个关系图可以分为以下几个区域：

左边区域——架构函数区域：这些函数并不针对某一特定的视频格式。
右上方黄色区域——协议处理函数区域：不同的协议（RTP，RTMP，FILE）会调用不同的协议处理函数。
右边中间绿色区域——封装格式处理函数区域：不同的封装格式（MKV，FLV，MPEG2TS，AVI）会调用不同的封装格式处理函数。
右边下方蓝色区域——编解码函数区域：不同的编码标准（HEVC，H.264，MPEG2）会调用不同的编解码函数。

箭头线

为了把调用关系表示的更明显，图中的箭头线也使用了不同的颜色：

红色的箭头线：标志了编码的流程。
其他颜色的箭头线：标志了函数之间的调用关系。其中：

调用 URLProtocol 结构体中的函数用黄色箭头线标识；
调用 AVOutputFormat 结构体中的函数用绿色箭头线标识；
调用 AVCodec 结构体中的函数用蓝色箭头线标识。

函数所在的文件

每个函数标识了它所在的文件路径。

左边区域（架构函数）
右上区域（URLProtocol 协议处理函数），URLProtocol 结构体包含如下协议处理函数指针：

url_open()：打开
url_read()：读取
url_write()：写入
url_seek()：调整进度
url_close()：关闭

下面举个例子，说明不同的协议对应着上述接口有不同的实现函数：

File 协议（即文件）对应的 URLProtocol 结构体 ff_file_protocol：

url_open() -> file_open() -> open()
url_read() -> file_read() -> read()
url_write() -> file_write() -> write()
url_seek() -> file_seek() -> lseek()
url_close() -> file_close() -> close()

RTMP 协议（libRTMP）对应的 URLProtocol 结构体 ff_librtmp_protocol：

url_open() -> rtmp_open() -> RTMP_Init()，RTMP_SetupURL()，RTMP_Connect()，RTMP_ConnectStream()
url_read() -> rtmp_read() -> RTMP_Read()
url_write() -> rtmp_write() -> RTMP_Write()
url_seek() -> rtmp_read_seek() -> RTMP_SendSeek()
url_close() -> rtmp_close() -> RTMP_Close()

UDP 协议对应的 URLProtocol 结构体 ff_udp_protocol：

url_open() -> udp_open()
url_read() -> udp_read()
url_write() -> udp_write()
url_seek() -> udp_close()
url_close() -> udp_close()

右中区域（AVOutputFormat 封装格式处理函数）

AVOutputFormat 包含如下封装格式处理函数指针：

write_header()：写文件头
write_packet()：写一帧数据
write_trailer()：写文件尾

下面举个例子，说明不同的封装格式对应着上述接口有不同的实现函数：

FLV 封装格式对应的 AVOutputFormat 结构体 ff_flv_muxer：

write_header() -> flv_write_header()
write_packet() – > flv_write_packet()
write_trailer() -> flv_write_trailer()

MKV 封装格式对应的 AVOutputFormat 结构体 ff_matroska_muxer：

write_header() -> mkv_write_header()
write_packet() – > mkv_write_flush_packet()
write_trailer() -> mkv_write_trailer()

MPEG2TS 封装格式对应的 AVOutputFormat 结构体 ff_mpegts_muxer：

write_header() -> mpegts_write_header()
write_packet() -> mpegts_write_packet()
write_trailer() -> mpegts_write_end()

AVI 封装格式对应的 AVOutputFormat 结构体 ff_avi_muxer：

write_header() -> avi_write_header()
write_packet() -> avi_write_packet()
write_trailer() -> avi_write_trailer()

右下区域（AVCodec 编解码函数）

AVCodec 包含如下编解码函数指针：

init()：初始化
encode2()：编码一帧数据
close()：关闭

下面举个例子，说明不同的编解码器对应着上述接口有不同的实现函数：

HEVC 编码器对应的 AVCodec 结构体 ff_libx265_encoder：

init() -> libx265_encode_init() -> x265_param_alloc()，x265_param_default_preset()，
x265_encoder_open()
encode2() -> libx265_encode_frame() -> x265_encoder_encode()
close() -> libx265_encode_close() -> x265_param_free()，x265_encoder_close()

H.264 编码器对应的 AVCodec 结构体 ff_libx264_encoder：

init() -> X264_init() -> x264_param_default()，x264_encoder_open()，x264_encoder_headers()
encode2() -> X264_frame() -> x264_encoder_encode()
close() -> X264_close() -> x264_encoder_close()

VP8 编码器（libVPX）对应的 AVCodec 结构体 ff_libvpx_vp8_encoder：

init() -> vpx_init() -> vpx_codec_enc_config_default()
encode2() -> vp8_encode() -> vpx_codec_enc_init(), vpx_codec_encode()
close() -> vp8_free() -> vpx_codec_destroy()

二、ffmpeg.h 头文件详解

ffmpeg.h 文件内容如下所示：

/*
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
#ifndef FFTOOLS_FFMPEG_H
#define FFTOOLS_FFMPEG_H
#include "config.h"
#include <stdint.h>
#include <stdio.h>
#include <signal.h>
#include "cmdutils.h"
#include "libavformat/avformat.h"
#include "libavformat/avio.h"
#include "libavcodec/avcodec.h"
#include "libavfilter/avfilter.h"
#include "libavutil/avutil.h"
#include "libavutil/dict.h"
#include "libavutil/eval.h"
#include "libavutil/fifo.h"
#include "libavutil/hwcontext.h"
#include "libavutil/pixfmt.h"
#include "libavutil/rational.h"
#include "libavutil/thread.h"
#include "libavutil/threadmessage.h"
#include "libswresample/swresample.h"
#define VSYNC_AUTO       -1
#define VSYNC_PASSTHROUGH 0
#define VSYNC_CFR         1
#define VSYNC_VFR         2
#define VSYNC_VSCFR       0xfe
#define VSYNC_DROP        0xff
#define MAX_STREAMS 1024    /* arbitrary sanity check value */
enum HWAccelID {
    HWACCEL_NONE = 0,
    HWACCEL_AUTO,
    HWACCEL_GENERIC,
    HWACCEL_VIDEOTOOLBOX,
    HWACCEL_QSV,
};
typedef struct HWAccel {
    const char *name;
    int (*init)(AVCodecContext *s);
    enum HWAccelID id;
    enum AVPixelFormat pix_fmt;
} HWAccel;
typedef struct HWDevice {
    const char *name;
    enum AVHWDeviceType type;
    AVBufferRef *device_ref;
} HWDevice;
/* select an input stream for an output stream */
typedef struct StreamMap {
    int disabled;           /* 1 is this mapping is disabled by a negative map */
    int file_index;
    int stream_index;
    int sync_file_index;
    int sync_stream_index;
    char *linklabel;       /* name of an output link, for mapping lavfi outputs */
} StreamMap;
typedef struct {
    int  file_idx,  stream_idx,  channel_idx; // input
    int ofile_idx, ostream_idx;               // output
} AudioChannelMap;
typedef struct OptionsContext {
    OptionGroup *g;
    /* input/output options */
    int64_t start_time;
    int64_t start_time_eof;
    int seek_timestamp;
    const char *format;
    SpecifierOpt *codec_names;
    int        nb_codec_names;
    SpecifierOpt *audio_channels;
    int        nb_audio_channels;
    SpecifierOpt *audio_sample_rate;
    int        nb_audio_sample_rate;
    SpecifierOpt *frame_rates;
    int        nb_frame_rates;
    SpecifierOpt *frame_sizes;
    int        nb_frame_sizes;
    SpecifierOpt *frame_pix_fmts;
    int        nb_frame_pix_fmts;
    /* input options */
    int64_t input_ts_offset;
    int loop;
    int rate_emu;
    int accurate_seek;
    int thread_queue_size;
    SpecifierOpt *ts_scale;
    int        nb_ts_scale;
    SpecifierOpt *dump_attachment;
    int        nb_dump_attachment;
    SpecifierOpt *hwaccels;
    int        nb_hwaccels;
    SpecifierOpt *hwaccel_devices;
    int        nb_hwaccel_devices;
    SpecifierOpt *hwaccel_output_formats;
    int        nb_hwaccel_output_formats;
    SpecifierOpt *autorotate;
    int        nb_autorotate;
    /* output options */
    StreamMap *stream_maps;
    int     nb_stream_maps;
    AudioChannelMap *audio_channel_maps; /* one info entry per -map_channel */
    int           nb_audio_channel_maps; /* number of (valid) -map_channel settings */
    int metadata_global_manual;
    int metadata_streams_manual;
    int metadata_chapters_manual;
    const char **attachments;
    int       nb_attachments;
    int chapters_input_file;
    int64_t recording_time;
    int64_t stop_time;
    uint64_t limit_filesize;
    float mux_preload;
    float mux_max_delay;
    int shortest;
    int bitexact;
    int video_disable;
    int audio_disable;
    int subtitle_disable;
    int data_disable;
    /* indexed by output file stream index */
    int   *streamid_map;
    int nb_streamid_map;
    SpecifierOpt *metadata;
    int        nb_metadata;
    SpecifierOpt *max_frames;
    int        nb_max_frames;
    SpecifierOpt *bitstream_filters;
    int        nb_bitstream_filters;
    SpecifierOpt *codec_tags;
    int        nb_codec_tags;
    SpecifierOpt *sample_fmts;
    int        nb_sample_fmts;
    SpecifierOpt *qscale;
    int        nb_qscale;
    SpecifierOpt *forced_key_frames;
    int        nb_forced_key_frames;
    SpecifierOpt *force_fps;
    int        nb_force_fps;
    SpecifierOpt *frame_aspect_ratios;
    int        nb_frame_aspect_ratios;
    SpecifierOpt *rc_overrides;
    int        nb_rc_overrides;
    SpecifierOpt *intra_matrices;
    int        nb_intra_matrices;
    SpecifierOpt *inter_matrices;
    int        nb_inter_matrices;
    SpecifierOpt *chroma_intra_matrices;
    int        nb_chroma_intra_matrices;
    SpecifierOpt *top_field_first;
    int        nb_top_field_first;
    SpecifierOpt *metadata_map;
    int        nb_metadata_map;
    SpecifierOpt *presets;
    int        nb_presets;
    SpecifierOpt *copy_initial_nonkeyframes;
    int        nb_copy_initial_nonkeyframes;
    SpecifierOpt *copy_prior_start;
    int        nb_copy_prior_start;
    SpecifierOpt *filters;
    int        nb_filters;
    SpecifierOpt *filter_scripts;
    int        nb_filter_scripts;
    SpecifierOpt *reinit_filters;
    int        nb_reinit_filters;
    SpecifierOpt *fix_sub_duration;
    int        nb_fix_sub_duration;
    SpecifierOpt *canvas_sizes;
    int        nb_canvas_sizes;
    SpecifierOpt *pass;
    int        nb_pass;
    SpecifierOpt *passlogfiles;
    int        nb_passlogfiles;
    SpecifierOpt *max_muxing_queue_size;
    int        nb_max_muxing_queue_size;
    SpecifierOpt *guess_layout_max;
    int        nb_guess_layout_max;
    SpecifierOpt *apad;
    int        nb_apad;
    SpecifierOpt *discard;
    int        nb_discard;
    SpecifierOpt *disposition;
    int        nb_disposition;
    SpecifierOpt *program;
    int        nb_program;
    SpecifierOpt *time_bases;
    int        nb_time_bases;
    SpecifierOpt *enc_time_bases;
    int        nb_enc_time_bases;
} OptionsContext;
typedef struct InputFilter {
    AVFilterContext    *filter;
    struct InputStream *ist;
    struct FilterGraph *graph;
    uint8_t            *name;
    enum AVMediaType    type;   // AVMEDIA_TYPE_SUBTITLE for sub2video
    AVFifoBuffer *frame_queue;
    // parameters configured for this input
    int format;
    int width, height;
    AVRational sample_aspect_ratio;
    int sample_rate;
    int channels;
    uint64_t channel_layout;
    AVBufferRef *hw_frames_ctx;
    int eof;
} InputFilter;
typedef struct OutputFilter {
    AVFilterContext     *filter;
    struct OutputStream *ost;
    struct FilterGraph  *graph;
    uint8_t             *name;
    /* temporary storage until stream maps are processed */
    AVFilterInOut       *out_tmp;
    enum AVMediaType     type;
    /* desired output stream properties */
    int width, height;
    AVRational frame_rate;
    int format;
    int sample_rate;
    uint64_t channel_layout;
    // those are only set if no format is specified and the encoder gives us multiple options
    int *formats;
    uint64_t *channel_layouts;
    int *sample_rates;
} OutputFilter;
typedef struct FilterGraph {
    int            index;
    const char    *graph_desc;
    AVFilterGraph *graph;
    int reconfiguration;
    InputFilter   **inputs;
    int          nb_inputs;
    OutputFilter **outputs;
    int         nb_outputs;
} FilterGraph;
typedef struct InputStream {
    int file_index;
    AVStream *st;
    int discard;             /* true if stream data should be discarded */
    int user_set_discard;
    int decoding_needed;     /* non zero if the packets must be decoded in 'raw_fifo', see DECODING_FOR_* */
#define DECODING_FOR_OST    1
#define DECODING_FOR_FILTER 2
    AVCodecContext *dec_ctx;
    AVCodec *dec;
    AVFrame *decoded_frame;
    AVFrame *filter_frame; /* a ref of decoded_frame, to be sent to filters */
    int64_t       start;     /* time when read started */
    /* predicted dts of the next packet read for this stream or (when there are
     * several frames in a packet) of the next frame in current packet (in AV_TIME_BASE units) */
    int64_t       next_dts;
    int64_t       dts;       ///< dts of the last packet read for this stream (in AV_TIME_BASE units)
    int64_t       next_pts;  ///< synthetic pts for the next decode frame (in AV_TIME_BASE units)
    int64_t       pts;       ///< current pts of the decoded frame  (in AV_TIME_BASE units)
    int           wrap_correction_done;
    int64_t filter_in_rescale_delta_last;
    int64_t min_pts; /* pts with the smallest value in a current stream */
    int64_t max_pts; /* pts with the higher value in a current stream */
    // when forcing constant input framerate through -r,
    // this contains the pts that will be given to the next decoded frame
    int64_t cfr_next_pts;
    int64_t nb_samples; /* number of samples in the last decoded audio frame before looping */
    double ts_scale;
    int saw_first_ts;
    AVDictionary *decoder_opts;
    AVRational framerate;               /* framerate forced with -r */
    int top_field_first;
    int guess_layout_max;
    int autorotate;
    int fix_sub_duration;
    struct { /* previous decoded subtitle and related variables */
        int got_output;
        int ret;
        AVSubtitle subtitle;
    } prev_sub;
    struct sub2video {
        int64_t last_pts;
        int64_t end_pts;
        AVFifoBuffer *sub_queue;    ///< queue of AVSubtitle* before filter init
        AVFrame *frame;
        int w, h;
        unsigned int initialize; ///< marks if sub2video_update should force an initialization
    } sub2video;
    int dr1;
    /* decoded data from this stream goes into all those filters
     * currently video and audio only */
    InputFilter **filters;
    int        nb_filters;
    int reinit_filters;
    /* hwaccel options */
    enum HWAccelID hwaccel_id;
    enum AVHWDeviceType hwaccel_device_type;
    char  *hwaccel_device;
    enum AVPixelFormat hwaccel_output_format;
    /* hwaccel context */
    void  *hwaccel_ctx;
    void (*hwaccel_uninit)(AVCodecContext *s);
    int  (*hwaccel_get_buffer)(AVCodecContext *s, AVFrame *frame, int flags);
    int  (*hwaccel_retrieve_data)(AVCodecContext *s, AVFrame *frame);
    enum AVPixelFormat hwaccel_pix_fmt;
    enum AVPixelFormat hwaccel_retrieved_pix_fmt;
    AVBufferRef *hw_frames_ctx;
    /* stats */
    // combined size of all the packets read
    uint64_t data_size;
    /* number of packets successfully read for this stream */
    uint64_t nb_packets;
    // number of frames/samples retrieved from the decoder
    uint64_t frames_decoded;
    uint64_t samples_decoded;
    int64_t *dts_buffer;
    int nb_dts_buffer;
    int got_output;
} InputStream;
typedef struct InputFile {
    AVFormatContext *ctx;
    int eof_reached;      /* true if eof reached */
    int eagain;           /* true if last read attempt returned EAGAIN */
    int ist_index;        /* index of first stream in input_streams */
    int loop;             /* set number of times input stream should be looped */
    int64_t duration;     /* actual duration of the longest stream in a file
                             at the moment when looping happens */
    AVRational time_base; /* time base of the duration */
    int64_t input_ts_offset;
    int64_t ts_offset;
    int64_t last_ts;
    int64_t start_time;   /* user-specified start time in AV_TIME_BASE or AV_NOPTS_VALUE */
    int seek_timestamp;
    int64_t recording_time;
    int nb_streams;       /* number of stream that ffmpeg is aware of; may be different
                             from ctx.nb_streams if new streams appear during av_read_frame() */
    int nb_streams_warn;  /* number of streams that the user was warned of */
    int rate_emu;
    int accurate_seek;
#if HAVE_THREADS
    AVThreadMessageQueue *in_thread_queue;
    pthread_t thread;           /* thread reading from this file */
    int non_blocking;           /* reading packets from the thread should not block */
    int joined;                 /* the thread has been joined */
    int thread_queue_size;      /* maximum number of queued packets */
#endif
} InputFile;
enum forced_keyframes_const {
    FKF_N,
    FKF_N_FORCED,
    FKF_PREV_FORCED_N,
    FKF_PREV_FORCED_T,
    FKF_T,
    FKF_NB
};
#define ABORT_ON_FLAG_EMPTY_OUTPUT        (1 <<  0)
#define ABORT_ON_FLAG_EMPTY_OUTPUT_STREAM (1 <<  1)
extern const char *const forced_keyframes_const_names[];
typedef enum {
    ENCODER_FINISHED = 1,
    MUXER_FINISHED = 2,
} OSTFinished ;
typedef struct OutputStream {
    int file_index;          /* file index */
    int index;               /* stream index in the output file */
    int source_index;        /* InputStream index */
    AVStream *st;            /* stream in the output file */
    int encoding_needed;     /* true if encoding needed for this stream */
    int frame_number;
    /* input pts and corresponding output pts
       for A/V sync */
    struct InputStream *sync_ist; /* input stream to sync against */
    int64_t sync_opts;       /* output frame counter, could be changed to some true timestamp */ // FIXME look at frame_number
    /* pts of the first frame encoded for this stream, used for limiting
     * recording time */
    int64_t first_pts;
    /* dts of the last packet sent to the muxer */
    int64_t last_mux_dts;
    // the timebase of the packets sent to the muxer
    AVRational mux_timebase;
    AVRational enc_timebase;
    AVBSFContext            *bsf_ctx;
    AVCodecContext *enc_ctx;
    AVCodecParameters *ref_par; /* associated input codec parameters with encoders options applied */
    AVCodec *enc;
    int64_t max_frames;
    AVFrame *filtered_frame;
    AVFrame *last_frame;
    int last_dropped;
    int last_nb0_frames[3];
    void  *hwaccel_ctx;
    /* video only */
    AVRational frame_rate;
    int is_cfr;
    int force_fps;
    int top_field_first;
    int rotate_overridden;
    double rotate_override_value;
    AVRational frame_aspect_ratio;
    /* forced key frames */
    int64_t forced_kf_ref_pts;
    int64_t *forced_kf_pts;
    int forced_kf_count;
    int forced_kf_index;
    char *forced_keyframes;
    AVExpr *forced_keyframes_pexpr;
    double forced_keyframes_expr_const_values[FKF_NB];
    /* audio only */
    int *audio_channels_map;             /* list of the channels id to pick from the source stream */
    int audio_channels_mapped;           /* number of channels in audio_channels_map */
    char *logfile_prefix;
    FILE *logfile;
    OutputFilter *filter;
    char *avfilter;
    char *filters;         ///< filtergraph associated to the -filter option
    char *filters_script;  ///< filtergraph script associated to the -filter_script option
    AVDictionary *encoder_opts;
    AVDictionary *sws_dict;
    AVDictionary *swr_opts;
    AVDictionary *resample_opts;
    char *apad;
    OSTFinished finished;        /* no more packets should be written for this stream */
    int unavailable;                     /* true if the steram is unavailable (possibly temporarily) */
    int stream_copy;
    // init_output_stream() has been called for this stream
    // The encoder and the bitstream filters have been initialized and the stream
    // parameters are set in the AVStream.
    int initialized;
    int inputs_done;
    const char *attachment_filename;
    int copy_initial_nonkeyframes;
    int copy_prior_start;
    char *disposition;
    int keep_pix_fmt;
    /* stats */
    // combined size of all the packets written
    uint64_t data_size;
    // number of packets send to the muxer
    uint64_t packets_written;
    // number of frames/samples sent to the encoder
    uint64_t frames_encoded;
    uint64_t samples_encoded;
    /* packet quality factor */
    int quality;
    int max_muxing_queue_size;
    /* the packets are buffered here until the muxer is ready to be initialized */
    AVFifoBuffer *muxing_queue;
    /* packet picture type */
    int pict_type;
    /* frame encode sum of squared error values */
    int64_t error[4];
} OutputStream;
typedef struct OutputFile {
    AVFormatContext *ctx;
    AVDictionary *opts;
    int ost_index;       /* index of the first stream in output_streams */
    int64_t recording_time;  ///< desired length of the resulting file in microseconds == AV_TIME_BASE units
    int64_t start_time;      ///< start time in microseconds == AV_TIME_BASE units
    uint64_t limit_filesize; /* filesize limit expressed in bytes */
    int shortest;
    int header_written;
} OutputFile;
extern InputStream **input_streams;
extern int        nb_input_streams;
extern InputFile   **input_files;
extern int        nb_input_files;
extern OutputStream **output_streams;
extern int         nb_output_streams;
extern OutputFile   **output_files;
extern int         nb_output_files;
extern FilterGraph **filtergraphs;
extern int        nb_filtergraphs;
extern char *vstats_filename;
extern char *sdp_filename;
extern float audio_drift_threshold;
extern float dts_delta_threshold;
extern float dts_error_threshold;
extern int audio_volume;
extern int audio_sync_method;
extern int video_sync_method;
extern float frame_drop_threshold;
extern int do_benchmark;
extern int do_benchmark_all;
extern int do_deinterlace;
extern int do_hex_dump;
extern int do_pkt_dump;
extern int copy_ts;
extern int start_at_zero;
extern int copy_tb;
extern int debug_ts;
extern int exit_on_error;
extern int abort_on_flags;
extern int print_stats;
extern int qp_hist;
extern int stdin_interaction;
extern int frame_bits_per_raw_sample;
extern AVIOContext *progress_avio;
extern float max_error_rate;
extern char *videotoolbox_pixfmt;
extern int filter_nbthreads;
extern int filter_complex_nbthreads;
extern int vstats_version;
extern const AVIOInterruptCB int_cb;
extern const OptionDef options[];
extern const HWAccel hwaccels[];
#if CONFIG_QSV
extern char *qsv_device;
#endif
extern HWDevice *filter_hw_device;
void term_init(void);
void term_exit(void);
void reset_options(OptionsContext *o, int is_input);
void show_usage(void);
void opt_output_file(void *optctx, const char *filename);
void remove_avoptions(AVDictionary **a, AVDictionary *b);
void assert_avoptions(AVDictionary *m);
int guess_input_channel_layout(InputStream *ist);
enum AVPixelFormat choose_pixel_fmt(AVStream *st, AVCodecContext *avctx, AVCodec *codec, enum AVPixelFormat target);
void choose_sample_fmt(AVStream *st, AVCodec *codec);
int configure_filtergraph(FilterGraph *fg);
int configure_output_filter(FilterGraph *fg, OutputFilter *ofilter, AVFilterInOut *out);
void check_filter_outputs(void);
int ist_in_filtergraph(FilterGraph *fg, InputStream *ist);
int filtergraph_is_simple(FilterGraph *fg);
int init_simple_filtergraph(InputStream *ist, OutputStream *ost);
int init_complex_filtergraph(FilterGraph *fg);
void sub2video_update(InputStream *ist, int64_t heartbeat_pts, AVSubtitle *sub);
int ifilter_parameters_from_frame(InputFilter *ifilter, const AVFrame *frame);
int ffmpeg_parse_options(int argc, char **argv);
int videotoolbox_init(AVCodecContext *s);
int qsv_init(AVCodecContext *s);
HWDevice *hw_device_get_by_name(const char *name);
int hw_device_init_from_string(const char *arg, HWDevice **dev);
void hw_device_free_all(void);
int hw_device_setup_for_decode(InputStream *ist);
int hw_device_setup_for_encode(OutputStream *ost);
int hw_device_setup_for_filter(FilterGraph *fg);
int hwaccel_decode_init(AVCodecContext *avctx);
int main_ffmpeg431(int argc, char** argv);
#endif /* FFTOOLS_FFMPEG_H */

全局变量与结构体：

输入：

InputStream **input_streams = NULL;
int nb_input_streams = 0;
InputFile **input_files = NULL;
int nb_input_files = 0;

输出：

OutputStream **output_streams = NULL;
int nb_output_streams = 0;
OutputFile **output_files = NULL;
int nb_output_files = 0;

其中： input_streams 是输入流的数组，nb_input_streams 是输入流的个数。 input_files 是输入文件（也可能是设备）的数组，nb_input_files 是输入文件的个数。下面的输出相关的变量们就不用解释了。

可以看出，文件和流是分别保存的。于是，可以想象，结构 InputStream 中应有其所属的文件在 InputFile 中的序号（file_index）。输入流数组应是这样填充的：每当在输入文件中找到一个流时，就把它添加到 input_streams 中，所以一个输入文件对应的输入流在 input_streams 中是紧靠着的，于是 InputFile 结构中应有其第一个流在 input_streams 中的开始序号（ist_index）和被放在 input_streams 中的流的总个数（nb_streams）。

在输出流 output_streams 中，除了要保存其所在的输出文件在 output_files 中的序号（index），还应保存其对应的输入流在 input_streams 中的序号（ source_index），也应保存其在所属输出文件中的流序号（file_index）。而输出文件中呢，只需保存它的第一个流在 output_streams 中的序号（ost_index）。

流和文件都准备好了，下面就是转换，那么转换过程是怎样的呢？

答：首先打开输入文件们，然后根据输入流们准备并打开解码器们，然后跟据输出流们准备并打开编码器们，然后创建输出文件们，然后为所有输出文件们写好头部，然后就在循环中把输入流转换到输出流并写入输出文件中，转换完后跳出循环，然后写入文件尾，最后关闭所有的输出文件

ffmpeg.c（4.3.1）源码剖析（二）https://developer.aliyun.com/article/1473998

ffmpeg.c（4.3.1）源码剖析（一）

前言

一、FFmpeg 源码结构图

二、ffmpeg.h 头文件详解

热门文章

最新文章

相关电子书

热门

活动广场

任务中心

开发者评测

高校计划

乘风者计划

训练营

阿里云MVP

话题

直播

下载

镜像站

技术资料

插件

ffmpeg.c（4.3.1）源码剖析（一）

前言

一、FFmpeg 源码结构图

二、ffmpeg.h 头文件详解

热门文章

最新文章

相关电子书