参考链接

• FFmpeg源代码结构图 - 解码_雷霄骅的博客-CSDN博客_ffmpeg雷霄骅

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，包含处理协议（Protocol）的功能。
  • 绿色背景的函数：AVInputFormat结构体中的函数，包含处理封装格式（Format）的功能。
  • 蓝色背景的函数：AVCodec结构体中的函数，包含了编解码器（Codec）的功能。
• PS：URLProtocol，AVInputFormat，AVCodec在FFmpeg开始运行并且注册完组件之后，都会分别被连接成一个个的链表。因此实际上是有很多的URLProtocol，AVInputFormat，AVCodec的。
• 图中画出了解码一个输入协议是“文件”（其实就是打开一个文件。“文件”也被当做是一种广义的协议），封装格式为FLV，视频编码格式是H.264的数据的函数调用关系。 

区域

• 整个架构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，通用架构，通用流程
• 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，MPEGTS，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：
• 黑色箭头线：标志了函数之间的调用关系。
• 红色的箭头线：标志了解码的流程。
• 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AVInputFormat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

• 每个函数旁边标识了它所在的文件的路径。
• 此外，还有一点需要注意的是，一些API函数内部也调用了另一些API函数。也就是说，API函数并不一定全部都调用FFmpeg的内部函数，他也有可能调用其他的API函数。
  • 例如从图中可以看出来，avformat_close_input()调用了avformat_free_context()和avio_close()。这些在内部代码中被调用的API函数也标记为粉红色。

现在的执行流程

• FFmpeg在avcodec.register_all被弃用后，新的流程_弥彦已死的博客-CSDN博客
• 从学龄前开始解读FFMPEG代码 之 avcodec_register_all函数_zzyincsdn的博客-CSDN博客

模块介绍 

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
• 结构体代码

typedef struct URLProtocol {const char *name;int     (*url_open)( URLContext *h, const char *url, int flags);/*** This callback is to be used by protocols which open further nested* protocols. options are then to be passed to ffurl_open_whitelist()* or ffurl_connect() for those nested protocols.*/int     (*url_open2)(URLContext *h, const char *url, int flags, AVDictionary **options);int     (*url_accept)(URLContext *s, URLContext **c);int     (*url_handshake)(URLContext *c);/*** Read data from the protocol.* If data is immediately available (even less than size), EOF is* reached or an error occurs (including EINTR), return immediately.* Otherwise:* In non-blocking mode, return AVERROR(EAGAIN) immediately.* In blocking mode, wait for data/EOF/error with a short timeout (0.1s),* and return AVERROR(EAGAIN) on timeout.* Checking interrupt_callback, looping on EINTR and EAGAIN and until* enough data has been read is left to the calling function; see* retry_transfer_wrapper in avio.c.*/int     (*url_read)( URLContext *h, unsigned char *buf, int size);int     (*url_write)(URLContext *h, const unsigned char *buf, int size);int64_t (*url_seek)( URLContext *h, int64_t pos, int whence);int     (*url_close)(URLContext *h);int (*url_read_pause)(URLContext *h, int pause);int64_t (*url_read_seek)(URLContext *h, int stream_index,int64_t timestamp, int flags);int (*url_get_file_handle)(URLContext *h);int (*url_get_multi_file_handle)(URLContext *h, int **handles,int *numhandles);int (*url_get_short_seek)(URLContext *h);int (*url_shutdown)(URLContext *h, int flags);const AVClass *priv_data_class;int priv_data_size;int flags;int (*url_check)(URLContext *h, int mask);int (*url_open_dir)(URLContext *h);int (*url_read_dir)(URLContext *h, AVIODirEntry **next);int (*url_close_dir)(URLContext *h);int (*url_delete)(URLContext *h);int (*url_move)(URLContext *h_src, URLContext *h_dst);const char *default_whitelist;
} URLProtocol;

 注意事项：

• 【例子】不同的协议对应着上述接口有不同的实现函数，举几个例子：
• File协议（即文件）对应的URLProtocol结构体ff_file_protocol：
• ff_file_protocol结构体的文件在<libavformat/file.c>
  • 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()

const URLProtocol ff_file_protocol = {.name                = "file",.url_open            = file_open,.url_read            = file_read,.url_write           = file_write,.url_seek            = file_seek,.url_close           = file_close,.url_get_file_handle = file_get_handle,.url_check           = file_check,.url_delete          = file_delete,.url_move            = file_move,.priv_data_size      = sizeof(FileContext),.priv_data_class     = &file_class,.url_open_dir        = file_open_dir,.url_read_dir        = file_read_dir,.url_close_dir       = file_close_dir,.default_whitelist   = "file,crypto,data"
};

• RTMP协议（libRTMP）对应的URLProtocol结构体ff_librtmp_protocol：
• ff_librtmp_protocol结构体的文件在<libavformat/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()

RTMP_CLASS(rtmp)
const URLProtocol ff_librtmp_protocol = {.name                = "rtmp",.url_open            = rtmp_open,.url_read            = rtmp_read,.url_write           = rtmp_write,.url_close           = rtmp_close,.url_read_pause      = rtmp_read_pause,.url_read_seek       = rtmp_read_seek,.url_get_file_handle = rtmp_get_file_handle,.priv_data_size      = sizeof(LibRTMPContext),.priv_data_class     = &librtmp_class,.flags               = URL_PROTOCOL_FLAG_NETWORK,
};

• UDP协议对应的URLProtocol结构体ff_udp_protocol：
• ff_udp_protocol结构体位于<libavformat/udp.c>
  • url_open() -> udp_open()
  • url_read() -> udp_read()
  • url_write() -> udp_write()
  • url_seek() -> udp_close()
  • url_close() -> udp_close()

const URLProtocol ff_udp_protocol = {.name                = "udp",.url_open            = udp_open,.url_read            = udp_read,.url_write           = udp_write,.url_close           = udp_close,.url_get_file_handle = udp_get_file_handle,.priv_data_size      = sizeof(UDPContext),.priv_data_class     = &udp_class,.flags               = URL_PROTOCOL_FLAG_NETWORK,
};

右中区域（AVInputFormat封装格式处理函数）

• AVInputFormat包含如下封装格式处理函数指针：
  • read_probe()：检查格式
  • read_header()：读取文件头
  • read_packet()：读取一帧数据
  • read_seek()：调整进度
  • read_close()：关闭

 注意事项：

• 【例子】不同的封装格式对应着上述接口有不同的实现函数，举几个例子：
• FLV封装格式对应的AVInputFormat结构体ff_flv_demuxer：
  • read_probe() -> flv_probe() –> probe()
  • read_header() -> flv_read_header() -> create_stream() -> avformat_new_stream()
  • read_packet() -> flv_read_packet()
  • read_seek() -> flv_read_seek()
  • read_close() -> flv_read_close()
• FFmpeg: libavformat/flvdec.c File Reference

= {.name           = "flv",.long_name      = NULL_IF_CONFIG_SMALL("FLV (Flash Video)"),.priv_data_size = sizeof(FLVContext),.read_probe     = flv_probe,.read_header    = flv_read_header,.read_packet    = flv_read_packet,.read_seek      = flv_read_seek,.read_close     = flv_read_close,.extensions     = "flv",.priv_class     = &flv_class,
}

• MKV封装格式对应的AVInputFormat结构体ff_matroska_demuxer：
  • read_probe() -> matroska_probe()
  • read_header() -> matroska_read_header()
  • read_packet() -> matroska_read_packet()
  • read_seek() -> matroska_read_seek()
  • read_close() -> matroska_read_close()
• 参考链接：FFmpeg: libavformat/matroskadec.c File Reference

= {.name           = "matroska,webm",.long_name      = NULL_IF_CONFIG_SMALL("Matroska / WebM"),.extensions     = "mkv,mk3d,mka,mks",.priv_data_size = sizeof(MatroskaDemuxContext),.read_probe     = matroska_probe,.read_header    = matroska_read_header,.read_packet    = matroska_read_packet,.read_close     = matroska_read_close,.read_seek      = matroska_read_seek,.mime_type      = "audio/webm,audio/x-matroska,video/webm,video/x-matroska"
}

• MPEG2TS封装格式对应的AVInputFormat结构体ff_mpegts_demuxer：
  • read_probe() -> mpegts_probe()
  • read_header() -> mpegts_read_header()
  • read_packet() -> mpegts_read_packet() 
  • read_close() -> mpegts_read_close()
• 参考链接：FFmpeg: libavformat/mpegts.c File Reference

= {.name           = "mpegts",.long_name      = NULL_IF_CONFIG_SMALL("MPEG-TS (MPEG-2 Transport Stream)"),.priv_data_size = sizeof(MpegTSContext),.read_probe     = mpegts_probe,.read_header    = mpegts_read_header,.read_packet    = mpegts_read_packet,.read_close     = mpegts_read_close,.read_timestamp = mpegts_get_dts,.flags          = AVFMT_SHOW_IDS | AVFMT_TS_DISCONT,.priv_class     = &mpegts_class,
}

• AVI封装格式对应的AVInputFormat结构体ff_avi_demuxer：
  • read_probe() -> avi_probe()
  • read_header() -> avi_read_header()
  • read_packet() -> avi_read_packet()
  • read_seek() -> avi_read_seek()
  • read_close() -> avi_read_close()
• 参考链接：FFmpeg: libavformat/avidec.c File Reference

= {.name           = "avi",.long_name      = NULL_IF_CONFIG_SMALL("AVI (Audio Video Interleaved)"),.priv_data_size = sizeof(AVIContext),.extensions     = "avi",.read_probe     = avi_probe,.read_header    = avi_read_header,.read_packet    = avi_read_packet,.read_close     = avi_read_close,.read_seek      = avi_read_seek,.priv_class = &demuxer_class,
}

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
  • decode()：解码一帧数据
  • close()：关闭
• 参考链接：FFmpeg: AVCodec Struct Reference
• 上述参考链接里面包含的结构体包含上述编解码函数指针
• 但是新版本好像没有了

typedef struct AVCodec {/*** Name of the codec implementation.* The name is globally unique among encoders and among decoders (but an* encoder and a decoder can share the same name).* This is the primary way to find a codec from the user perspective.*/const char *name;/*** Descriptive name for the codec, meant to be more human readable than name.* You should use the NULL_IF_CONFIG_SMALL() macro to define it.*/const char *long_name;enum AVMediaType type;enum AVCodecID id;/*** Codec capabilities.* see AV_CODEC_CAP_**/int capabilities;uint8_t max_lowres;                     ///< maximum value for lowres supported by the decoderconst AVRational *supported_framerates; ///< array of supported framerates, or NULL if any, array is terminated by {0,0}const enum AVPixelFormat *pix_fmts;     ///< array of supported pixel formats, or NULL if unknown, array is terminated by -1const int *supported_samplerates;       ///< array of supported audio samplerates, or NULL if unknown, array is terminated by 0const enum AVSampleFormat *sample_fmts; ///< array of supported sample formats, or NULL if unknown, array is terminated by -1
#if FF_API_OLD_CHANNEL_LAYOUT/*** @deprecated use ch_layouts instead*/attribute_deprecatedconst uint64_t *channel_layouts;         ///< array of support channel layouts, or NULL if unknown. array is terminated by 0
#endifconst AVClass *priv_class;              ///< AVClass for the private contextconst AVProfile *profiles;              ///< array of recognized profiles, or NULL if unknown, array is terminated by {FF_PROFILE_UNKNOWN}/*** Group name of the codec implementation.* This is a short symbolic name of the wrapper backing this codec. A* wrapper uses some kind of external implementation for the codec, such* as an external library, or a codec implementation provided by the OS or* the hardware.* If this field is NULL, this is a builtin, libavcodec native codec.* If non-NULL, this will be the suffix in AVCodec.name in most cases* (usually AVCodec.name will be of the form "<codec_name>_<wrapper_name>").*/const char *wrapper_name;/*** Array of supported channel layouts, terminated with a zeroed layout.*/const AVChannelLayout *ch_layouts;
} AVCodec;

 注意事项：

• 【例子】不同的编解码器对应着上述接口有不同的实现函数，举几个例子：
• HEVC解码对应的AVCodec结构体ff_hevc_decoder：
  • init() -> hevc_decode_init()
  • decode() -> hevc_decode_frame() -> decode_nal_units()
  • close() -> hevc_decode_free()
• 参考链接：FFmpeg: libavcodec/hevc.c File Reference

= {.name                  = "hevc",.long_name             = NULL_IF_CONFIG_SMALL("HEVC (High Efficiency Video Coding)"),.type                  = AVMEDIA_TYPE_VIDEO,.id                    = AV_CODEC_ID_HEVC,.priv_data_size        = sizeof(HEVCContext),.priv_class            = &hevc_decoder_class,.init                  = hevc_decode_init,.close                 = hevc_decode_free,.decode                = ,.flush                 = hevc_decode_flush,.update_thread_context = hevc_update_thread_context,.init_thread_copy      = hevc_init_thread_copy,.capabilities          = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_DELAY |AV_CODEC_CAP_SLICE_THREADS | AV_CODEC_CAP_FRAME_THREADS,.profiles              = NULL_IF_CONFIG_SMALL(profiles),
}

• H.264解码对应的AVCodec结构体ff_h264_decoder：
  • init() -> ff_h264_decode_init()
  • decode() -> h264_decode_frame() -> decode_nal_units()
  • close() -> h264_decode_end()
• 参考链接：FFmpeg: libavcodec/h264.c File Reference

= {.name                  = "h264",.long_name             = NULL_IF_CONFIG_SMALL("H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10"),.type                  = AVMEDIA_TYPE_VIDEO,.id                    = AV_CODEC_ID_H264,.priv_data_size        = sizeof(H264Context),.init                  = ff_h264_decode_init,.close                 = h264_decode_end,.decode                = h264_decode_frame,.capabilities          =  AV_CODEC_CAP_DR1 |AV_CODEC_CAP_DELAY | AV_CODEC_CAP_SLICE_THREADS |AV_CODEC_CAP_FRAME_THREADS,.flush                 = flush_dpb,.init_thread_copy      = ONLY_IF_THREADS_ENABLED(decode_init_thread_copy),.update_thread_context = ONLY_IF_THREADS_ENABLED(ff_h264_update_thread_context),.profiles              = NULL_IF_CONFIG_SMALL(profiles),.priv_class            = &h264_class,
}

• VP8解码（libVPX）对应的AVCodec结构体ff_libvpx_vp8_decoder：
  • init() -> vpx_init() -> vpx_codec_dec_init()
  • decode() -> vp8_decode() -> vpx_codec_decode(), vpx_codec_get_frame()
  • close() -> vp8_free() -> vpx_codec_destroy()
• 版本差异
• 参考链接：FFmpeg: libavcodec/libvpxdec.c Source File

AVCodec ff_libvpx_vp8_decoder = {.name           = "libvpx",.type           = AVMEDIA_TYPE_VIDEO,.id             = AV_CODEC_ID_VP8,.priv_data_size = sizeof(VP8Context),.init           = vp8_init,.close          = vp8_free,.decode         = vp8_decode,.capabilities   = CODEC_CAP_AUTO_THREADS | CODEC_CAP_DR1,.long_name      = NULL_IF_CONFIG_SMALL("libvpx VP8"),
};

• MPEG2解码对应的AVCodec结构体ff_mpeg2video_decoder：
  • init() -> mpeg_decode_init()
  • decode() -> mpeg_decode_frame()
  • close() -> mpeg_decode_end()
• 参考链接：FFmpeg: libavcodec/mpeg12dec.c File Reference

= {.name           = "mpeg2video",.long_name      = NULL_IF_CONFIG_SMALL("MPEG-2 video"),.type           = AVMEDIA_TYPE_VIDEO,.id             = AV_CODEC_ID_MPEG2VIDEO,.priv_data_size = sizeof(Mpeg1Context),.init           = mpeg_decode_init,.close          = mpeg_decode_end,.decode         = mpeg_decode_frame,.capabilities   = AV_CODEC_CAP_DRAW_HORIZ_BAND | AV_CODEC_CAP_DR1 |AV_CODEC_CAP_TRUNCATED | AV_CODEC_CAP_DELAY |AV_CODEC_CAP_SLICE_THREADS,.flush          = flush,.max_lowres     = 3,.profiles       = NULL_IF_CONFIG_SMALL(mpeg2_video_profiles),
}

 注意事项

• FFmpeg (libav*) 开发踩过的坑 - 哔哩哔哩