rtsp url播放的时候，会根据url中是否有rtsp来判断是否调用ff_rtsp_demuxer进行网络数据的读取

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AVInputFormatff_rtsp_demuxer = {
    .name           = "rtsp",
    .long_name      = NULL_IF_CONFIG_SMALL("RTSP input"),
    .priv_data_size = sizeof(RTSPState),
    .read_probe     = rtsp_probe,
    .read_header    = rtsp_read_header,
    .read_packet    = rtsp_read_packet,
    .read_close     = rtsp_read_close,
    .read_seek      = rtsp_read_seek,
    .flags          = AVFMT_NOFILE,
    .read_play      = rtsp_read_play,
    .read_pause     = rtsp_read_pause,
    .priv_class     = &rtsp_demuxer_class,
};

码流格式探测分析

> ffplayd.exe!rtp_read(URLContext * h, unsigned char * buf, int size) 行 377 C

    (调用recvfrom读取RTP传输数据,transfer_func指向了rtp_read的实现)

  ffplayd.exe!retry_transfer_wrapper(URLContext * h, unsigned char * buf, int size, int size_min, int (URLContext *, unsigned char *, int) * transfer_func) 行 376 C
  ffplayd.exe!ffurl_read(URLContext * h, unsigned char * buf, int size) 行 412 C
  ffplayd.exe!udp_read_packet(AVFormatContext * s, RTSPStream * * prtsp_st, unsigned char * buf, int buf_size, __int64 wait_end) 行 2033 C
  ffplayd.exe!read_packet(AVFormatContext * s, RTSPStream * * rtsp_st, RTSPStream * first_queue_st, __int64 wait_end) 行 2116 C
  ffplayd.exe!ff_rtsp_fetch_packet(AVFormatContext * s, AVPacket * pkt) 行 2202 C
  ffplayd.exe!rtsp_read_packet(AVFormatContext * s, AVPacket * pkt) 行 879 C
  ffplayd.exe!ff_read_packet(AVFormatContext * s, AVPacket * pkt) 行 856 C
  ffplayd.exe!read_frame_internal(AVFormatContext * s, AVPacket * pkt) 行 1582 C
  ffplayd.exe!avformat_find_stream_info(AVFormatContext * ic, AVDictionary * * options) 行 3772 C
  ffplayd.exe!read_thread(void * arg) 行 2805 C
  ffplayd.exe!SDL_RunThread(void * data) 行 283 C
  ffplayd.exe!RunThread(void * data) 行 91 C
  ffplayd.exe!RunThreadViaBeginThreadEx(void * data) 行 106 

重点分析函数ff_rtsp_fetch_packet，该函数调用read_packet获取到RTP数据，调用ff_rtp_parse_packet分析RTP数据，去掉RTP包头，添加起始码，然后封装成AVPacket，但是封装的AVPacket并不是完整的NAL单元的视频流，对于FU-A分包的数据，仍然需要对多个AVPacket进行重新组装

> ffplayd.exe!h364_handle_packet_fu_a(AVFormatContext * ctx, PayloadContext * data, AVPacket * pkt, const unsigned char * buf, int len, int * nal_counters, int nal_mask) 行 291 C

(对FU-A分包的RTP格式数据，会根据是否是第一个包添加起始码，关键是start_bit    = fu_header >> 7;)
  ffplayd.exe!h364_handle_packet(AVFormatContext * ctx, PayloadContext * data, AVStream * st, AVPacket * pkt, unsigned int * timestamp, const unsigned char * buf, int len, unsigned short seq, int flags) 行 359 C
  ffplayd.exe!rtp_parse_packet_internal(RTPDemuxContext * s, AVPacket * pkt, const unsigned char * buf, int len) 行 692 C
  ffplayd.exe!rtp_parse_one_packet(RTPDemuxContext * s, AVPacket * pkt, unsigned char * * bufptr, int len) 行 841 C
  ffplayd.exe!ff_rtp_parse_packet(RTPDemuxContext * s, AVPacket * pkt, unsigned char * * bufptr, int len) 行 875 C
  ffplayd.exe!ff_rtsp_fetch_packet(AVFormatContext * s, AVPacket * pkt) 行 2217 C
  ffplayd.exe!rtsp_read_packet(AVFormatContext * s, AVPacket * pkt) 行 879 C
  ffplayd.exe!ff_read_packet(AVFormatContext * s, AVPacket * pkt) 行 856 C
  ffplayd.exe!read_frame_internal(AVFormatContext * s, AVPacket * pkt) 行 1582 C
  ffplayd.exe!av_read_frame(AVFormatContext * s, AVPacket * pkt) 行 1776 C
  ffplayd.exe!read_thread(void * arg) 行 3008 C
  ffplayd.exe!SDL_RunThread(void * data) 行 283 C
  ffplayd.exe!RunThread(void * data) 行 91 C
  ffplayd.exe!RunThreadViaBeginThreadEx(void * data) 行 106 C

av_read_frame分包代码剖析

  ffplayd.exe!ff_combine_frame(ParseContext * pc, int next, const unsigned char * * buf, int * buf_size) 行 265 C
> ffplayd.exe!h364_parse(AVCodecParserContext * s, AVCodecContext * avctx, const unsigned char * * poutbuf, int * poutbuf_size, const unsigned char * buf, int buf_size) 行 595 C
  ffplayd.exe!av_parser_parse2(AVCodecParserContext * s, AVCodecContext * avctx, unsigned char * * poutbuf, int * poutbuf_size, const unsigned char * buf, int buf_size, __int64 pts, __int64 dts, __int64 pos) 行 166 C
  ffplayd.exe!parse_packet(AVFormatContext * s, AVPacket * pkt, int stream_index) 行 1461 C
  ffplayd.exe!read_frame_internal(AVFormatContext * s, AVPacket * pkt) 行 1675 C
  ffplayd.exe!av_read_frame(AVFormatContext * s, AVPacket * pkt) 行 1776 C
  ffplayd.exe!read_thread(void * arg) 行 3008 C
  ffplayd.exe!SDL_RunThread(void * data) 行 283 C
  ffplayd.exe!RunThread(void * data) 行 91 C
  ffplayd.exe!RunThreadViaBeginThreadEx(void * data) 行 106 C
  [外部代码] 

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