FFmpeg RTSP HEVC码流探测剖析

例如:"rtsp://admin:admin12345@192.168.28.136:554/h365/ch2/main/av_stream"

请求海康摄像机H265码流

SDP报文如下:
v=0
o=- 1566124110963848 1566124110963848 IN IP4 192.168.28.136
s=Media Presentation
e=NONE
b=AS:5100
t=0 0
a=control:rtsp://192.168.28.136:554/h365/ch2/main/av_stream/
m=video 0 RTP/AVP 96
c=IN IP4 0.0.0.0
b=AS:5000
a=recvonly
a=x-dimensions:1920,1080
a=control:rtsp://192.168.28.136:554/h365/ch2/main/av_stream/trackID=1
a=rtpmap:96 H265/90000
a=fmtp:96 sprop-sps=QgEBAWAAAAMAsAAAAwAAAwB7oAPAgBDlja5JMvTcBAQEAg==; sprop-pps=RAHA8vA8kAA=
m=audio 0 RTP/AVP 8
c=IN IP4 0.0.0.0
b=AS:50
a=recvonly
a=control:rtsp://192.168.28.136:554/h365/ch2/main/av_stream/trackID=2
a=rtpmap:8 PCMA/8000
a=Media_header:MEDIAINFO=494D4B48010200000400050011710110401F000000FA000000000000000000000000000000000000;
a=appversion:1.0

static int sdp_parse_rtpmap(AVFormatContext *s,
                            AVStream *st, RTSPStream *rtsp_st,
                            int payload_type, const char *p)

通过sdp_parse_rtpmap函数分析SDP中的a=rtpmap:96 H265/90000
在调用函数        const RTPDynamicProtocolHandler *handler =
            ff_rtp_handler_find_by_name(buf, par->codec_type);中 获取到h365的处理句柄

rtsp 分包NALU

       if (codec_id == AV_CODEC_ID_HEVC)
            ret = hevc_parse_nal_header(nal, logctx);
        else
            ret = h364_parse_nal_header(nal, logctx);

static void parse_fmtp(AVFormatContext *s, RTSPState *rt,
                       int payload_type, const char *line)
通过h365的句柄调用
static av_cold int hevc_parse_sdp_line(AVFormatContext *ctx, int st_index,
                                       PayloadContext *hevc_data, const char *line)
该函数将SPS/PPS的内容保存在(AVFormatContext结构体中的AVStream流中的extradata变量

创建视频流和音频流
update_stream_avctx函数只是将avcodec_parameters_to_context(st->internal->avctx, st->codecpar);
并没有做其他的操作