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FFmpeg rtsp播放代码剖析

发表于:2022-08-20 作者:安全数据网编辑
编辑最后更新 2022年08月20日,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AVInputFormatff_rtsp_demuxer = {.name = "

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

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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