參考鏈接

FFmpeg源代碼結構圖 - 解碼_雷霄驊的博客-CSDN博客_ffmpeg雷霄驊

函數背景色

函數在圖中以方框的形式表現出來。不同的背景色標志了該函數不同的作用：
- 粉紅色背景函數：FFmpeg的API函數。
- 白色背景的函數：FFmpeg的內部函數。
- 黃色背景的函數：URLProtocol結構體中的函數，包含處理協議（Protocol）的功能。
- 綠色背景的函數：AVInputFormat結構體中的函數，包含處理封裝格式（Format）的功能。
- 藍色背景的函數：AVCodec結構體中的函數，包含了編解碼器（Codec）的功能。
PS：URLProtocol，AVInputFormat，AVCodec在FFmpeg開始運行并且注冊完組件之后，都會分別被連接成一個個的鏈表。因此實際上是有很多的URLProtocol，AVInputFormat，AVCodec的。
圖中畫出了解碼一個輸入協議是“文件”（其實就是打開一個文件。“文件”也被當做是一種廣義的協議），封裝格式為FLV，視頻編碼格式是H.264的數據的函數調用關系。?

區域

整個架構圖可以分為以下幾個區域：
左邊區域——架構函數區域：這些函數并不針對某一特定的視頻格式，通用架構，通用流程
右上方黃色區域——協議處理函數區域：不同的協議（RTP，RTMP，FILE）會調用不同的協議處理函數。
右邊中間綠色區域——封裝格式處理函數區域：不同的封裝格式（MKV，FLV，MPEGTS，AVI）會調用不同的封裝格式處理函數。
右邊下方藍色區域——編解碼函數區域：不同的編碼標準（HEVC，H.264，MPEG2）會調用不同的編解碼函數。

箭頭線

為了把調用關系表示的更明顯，圖中的箭頭線也使用了不同的顏色：
黑色箭頭線：標志了函數之間的調用關系。
紅色的箭頭線：標志了解碼的流程。
其他顏色的箭頭線：標志了函數之間的調用關系。其中：
- 調用URLProtocol結構體中的函數用黃色箭頭線標識；
- 調用AVInputFormat結構體中的函數用綠色箭頭線標識；
- 調用AVCodec結構體中的函數用藍色箭頭線標識。

函數所在的文件

每個函數旁邊標識了它所在的文件的路徑。
此外，還有一點需要注意的是，一些API函數內部也調用了另一些API函數。也就是說，API函數并不一定全部都調用FFmpeg的內部函數，他也有可能調用其他的API函數。
- 例如從圖中可以看出來，avformat_close_input()調用了avformat_free_context()和avio_close()。這些在內部代碼中被調用的API函數也標記為粉紅色。

現在的執行流程

FFmpeg在avcodec.register_all被棄用后，新的流程_彌彥已死的博客-CSDN博客
從學齡前開始解讀FFMPEG代碼之 avcodec_register_all函數_zzyincsdn的博客-CSDN博客

模塊介紹?

右上區域（URLProtocol協議處理函數）

URLProtocol結構體包含如下協議處理函數指針：
- url_open()：打開
- url_read()：讀取
- url_write()：寫入
- url_seek()：調整進度
- url_close()：關閉
結構體代碼

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;

?注意事項：

【例子】不同的協議對應著上述接口有不同的實現函數，舉幾個例子：
File協議（即文件）對應的URLProtocol結構體ff_file_protocol：
ff_file_protocol結構體的文件在<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協議（libRTMP）對應的URLProtocol結構體ff_librtmp_protocol：
ff_librtmp_protocol結構體的文件在<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協議對應的URLProtocol結構體ff_udp_protocol：
ff_udp_protocol結構體位于<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,
};

右中區域（AVInputFormat封裝格式處理函數）

AVInputFormat包含如下封裝格式處理函數指針：
- read_probe()：檢查格式
- read_header()：讀取文件頭
- read_packet()：讀取一幀數據
- read_seek()：調整進度
- read_close()：關閉

?注意事項：

【例子】不同的封裝格式對應著上述接口有不同的實現函數，舉幾個例子：
FLV封裝格式對應的AVInputFormat結構體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封裝格式對應的AVInputFormat結構體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()
參考鏈接：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封裝格式對應的AVInputFormat結構體ff_mpegts_demuxer：
- read_probe() -> mpegts_probe()
- read_header() -> mpegts_read_header()
- read_packet() -> mpegts_read_packet()?
- read_close() -> mpegts_read_close()
參考鏈接：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封裝格式對應的AVInputFormat結構體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()
參考鏈接：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,
}

右下區域（AVCodec編解碼函數）

AVCodec包含如下編解碼函數指針：
- init()：初始化
- decode()：解碼一幀數據
- close()：關閉
參考鏈接：FFmpeg: AVCodec Struct Reference
上述參考鏈接里面包含的結構體包含上述編解碼函數指針
但是新版本好像沒有了

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;

?注意事項：

【例子】不同的編解碼器對應著上述接口有不同的實現函數，舉幾個例子：
HEVC解碼對應的AVCodec結構體ff_hevc_decoder：
- init() -> hevc_decode_init()
- decode() -> hevc_decode_frame() -> decode_nal_units()
- close() -> hevc_decode_free()
參考鏈接：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解碼對應的AVCodec結構體ff_h264_decoder：
- init() -> ff_h264_decode_init()
- decode() -> h264_decode_frame() -> decode_nal_units()
- close() -> h264_decode_end()
參考鏈接：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解碼（libVPX）對應的AVCodec結構體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()
版本差異
參考鏈接：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解碼對應的AVCodec結構體ff_mpeg2video_decoder：
- init() -> mpeg_decode_init()
- decode() -> mpeg_decode_frame()
- close() -> mpeg_decode_end()
參考鏈接：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),
}