接收Nack的调用栈

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Call::DeliverPacket

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RTCP包的判断

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  1. H:\webrtc-20210315\webrtc-20210315\webrtc\webrtc-checkout\src\call\call.cc
  2. bool IsRtcp(const uint8_t* packet, size_t length) {
  3.   RtpUtility::RtpHeaderParser rtp_parser(packet, length);
  4.   return rtp_parser.RTCP();
  5. }
  7. H:\webrtc-20210315\webrtc-20210315\webrtc\webrtc-checkout\src\modules\rtp_rtcp\source\rtp_utility.cc
  8. bool RtpHeaderParser::RTCP() const {
  9.   // 72 to 76 is reserved for RTP
  10.   // 77 to 79 is not reserver but  they are not assigned we will block them
  11.   // for RTCP 200 SR  == marker bit + 72
  12.   // for RTCP 204 APP == marker bit + 76
  13.   /*
  14.    *       RTCP
  15.    *
  16.    * FIR      full INTRA-frame request             192     [RFC2032]   supported
  17.    * NACK     negative acknowledgement             193     [RFC2032]
  18.    * IJ       Extended inter-arrival jitter report 195 [RFC-ietf-avt-rtp-toff
  19.    * set-07.txt] http://tools.ietf.org/html/draft-ietf-avt-rtp-toffset-07
  20.    * SR       sender report                        200     [RFC3551]   supported
  21.    * RR       receiver report                      201     [RFC3551]   supported
  22.    * SDES     source description                   202     [RFC3551]   supported
  23.    * BYE      goodbye                              203     [RFC3551]   supported
  24.    * APP      application-defined                  204     [RFC3551]   ignored
  25.    * RTPFB    Transport layer FB message           205     [RFC4585]   supported
  26.    * PSFB     Payload-specific FB message          206     [RFC4585]   supported
  27.    * XR       extended report                      207     [RFC3611]   supported
  28.    */
  30.   /* 205       RFC 5104
  31.    * FMT 1      NACK       supported
  32.    * FMT 2      reserved
  33.    * FMT 3      TMMBR      supported
  34.    * FMT 4      TMMBN      supported
  35.    */
  37.   /* 206      RFC 5104
  38.    * FMT 1:     Picture Loss Indication (PLI)                      supported
  39.    * FMT 2:     Slice Lost Indication (SLI)
  40.    * FMT 3:     Reference Picture Selection Indication (RPSI)
  41.    * FMT 4:     Full Intra Request (FIR) Command                   supported
  42.    * FMT 5:     Temporal-Spatial Trade-off Request (TSTR)
  43.    * FMT 6:     Temporal-Spatial Trade-off Notification (TSTN)
  44.    * FMT 7:     Video Back Channel Message (VBCM)
  45.    * FMT 15:    Application layer FB message
  46.    */
  48.   const ptrdiff_t length = _ptrRTPDataEnd - _ptrRTPDataBegin;
  49.   if (length < kRtcpMinHeaderLength) {
  50.     return false;
  51.   }
  53.   const uint8_t V = _ptrRTPDataBegin[0] >> 6;
  54.   if (V != kRtcpExpectedVersion) {
  55.     return false;
  56.   }
  58.   const uint8_t payloadType = _ptrRTPDataBegin[1];
  59.   switch (payloadType) {
  60.     case 192:
  61.       return true;
  62.     case 193:
  63.       // not supported
  64.       // pass through and check for a potential RTP packet
  65.       return false;
  66.     case 195:
  67.     case 200:
  68.     case 201:
  69.     case 202:
  70.     case 203:
  71.     case 204:
  72.     case 205:
  73.     case 206:
  74.     case 207:
  75.       return true;
  76.     default:
  77.       return false;
  78.   }
  79. }

RTCPReceiver::IncomingPacket

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ParseCompoundPacket 解析联合包， 联合包就是将多个rtcp包组合起来为一个UDP包发送出去。
多个RTCP包如何解析？ 通过解析每一个包的长度来，找到长度后，拿出该长度的内容解析出该包。

ParseCompoundPacket

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PacketInformation

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