RTCP实现代码分析 | 易学教程

场景

RTP over TCP中 RTCP的实现代码

std::string strName = "fengyuzaitu@51.cto";
int nLength = 2 + 2 + 8 + 20 + 4 + 6 + strName.size();
std::string strRTCPBuffer;

//对齐四个字节，并且让最后的字符是0x00,保证wireshark抓包最后显示Type: END (0)

int nRet = (strName.length() + 2) % 4;
  if (0 != nRet)
  {
   nLength = nLength + 4 - nRet;
  }
  else
  {
   nLength = nLength + 4;
  }
  strRTCPBuffer.resize(nLength);

//$+channel
  strRTCPBuffer[0] = 0x24;
  strRTCPBuffer[1] = 0x01;
  //RTCP报文长度，一段是RTCP统计数据内容，一段是RTCP源描述
  *(unsigned short*)&strRTCPBuffer[3] = htons(nLength - 4);
  //Sender Report
  strRTCPBuffer[4] = (char)(2 << 6);                              // V=2, P=RC=0
  strRTCPBuffer[5] = (char)200;                                 // PT=SR=200
  *(unsigned short*)&strRTCPBuffer[6] = htons(6);     // 7个32比特减一
  *(unsigned int*)&strRTCPBuffer[8] = htonl(m_n***c);
  *(unsigned int*)&strRTCPBuffer[12] = htonl(m_video.sendtime >> 32);        // High 32-bits
  *(unsigned int*)&strRTCPBuffer[16] = htonl(m_video.sendtime & 0xFFFFFFFF); // Low 32-bits
  *(unsigned int*)&strRTCPBuffer[20] = htonl(m_nRtpTime);
  *(unsigned int*)&strRTCPBuffer[24] = htonl(m_nSendPacketCount);
  *(unsigned int*)&strRTCPBuffer[28] = htonl(m_nSendLength);
  //Source description
  strRTCPBuffer[32] = (char)(2 << 6) + 1;                          // V=2, P=0, SC=1
  strRTCPBuffer[33] = 202;
  //RTCP源描述长度,减去4个字节($+channel+2个字节长度)减去Sender Report报文长度
  *(unsigned short*)&strRTCPBuffer[34] = htons((nLength - 4 - 7*4)/4 - 1);
  *(unsigned int*)&strRTCPBuffer[39] = htonl(m_n***c);
  strRTCPBuffer[40] = 1;                                         // CNAME=1
  strRTCPBuffer[41] = (char)strName.size();
  memcpy(&strRTCPBuffer[42], strName.c_str(), strName.size());

wireshark抓包展示内容：

Frame 151081: 118 bytes on wire (944 bits), 118 bytes captured (944 bits) on interface 0
Ethernet II, Src: Clevo_5a:e2:a6 (80:fa:5b:5a:e2:a6), Dst: c4:b8:b4:01:56:de (c4:b8:b4:01:56:de)
Internet Protocol Version 4, Src: 192.168.58.173, Dst: 192.168.10.162
Transmission Control Protocol, Src Port: 554, Dst Port: 6470, Seq: 29276514, Ack: 1506, Len: 64
RTSP Interleaved Frame, Channel: 0x01, 60 bytes
    Magic: 0x24
    Channel: 0x01
    Length: 60
Real-time Transport Control Protocol (Sender Report)
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0000 = Reception report count: 0
    Packet type: Sender Report (200)
    Length: 6 (28 bytes)
    Sender ***C: 0xdb7c74bd (3682366653)
    Timestamp, MSW: 0 (0x00000000)
    Timestamp, LSW: 449468312 (0x1aca5798)
    [MSW and LSW as NTP timestamp: Jan 1, 1970 00:00:00.104649996 UTC]
    RTP timestamp: 897337600
    Sender's packet count: 24924
    Sender's octet count: 28834770
Real-time Transport Control Protocol (Source description)
    10.. .... = Version: RFC 1889 Version (2)
    ..0. .... = Padding: False
    ...0 0001 = Source count: 1
    Packet type: Source description (202)
    Length: 7 (32 bytes)
    Chunk 1, ***C/CSRC 0xDB
        Identifier: 0x000000db (219)
        SDES items
            Type: CNAME (user and domain) (1)
            Length: 18
            Text: fengyuzaitu@51.cto
            Type: END (0)
[RTCP frame length check: OK - 60 bytes]

来源：oschina

链接：https://my.oschina.net/u/4296417/blog/4277216

标签

wireshark

xDB

mvideo

rtp

Transmission

ntp