=====================================================

RTMPdump(libRTMP) 源代码分析系列文章:

RTMPdump 源代码分析 1: main()函数

RTMPDump (libRTMP) 源代码分析2:解析RTMP地址——RTMP_ParseURL()

RTMPdump (libRTMP) 源代码分析3: AMF编码

RTMPdump (libRTMP) 源代码分析4: 连接第一步——握手 (HandShake)

RTMPdump (libRTMP) 源代码分析5: 建立一个流媒体连接  (NetConnection部分)

RTMPdump (libRTMP) 源代码分析6: 建立一个流媒体连接  (NetStream部分 1)

RTMPdump (libRTMP) 源代码分析7: 建立一个流媒体连接  (NetStream部分 2)

RTMPdump (libRTMP) 源代码分析8: 发送消息 (Message)

RTMPdump (libRTMP) 源代码分析9: 接收消息 (Message)  (接收视音频数据)

RTMPdump (libRTMP) 源代码分析10: 处理各种消息 (Message)

=====================================================

函数调用结构图

RTMPDump (libRTMP)的整体的函数调用结构图如下图所示。

单击查看大图

详细分析

前文已经分析了 RTMPdump中建立一个NetConnection的过程:RTMPdump 源代码分析 5: 建立一个流媒体连接 (NetConnection部分)

多余的话不多说,下面先来看看RTMP_ConnectStream(),该函数主要用于在NetConnection基础上建立一个NetStream。

RTMP_ConnectStream()

//创建流
int
RTMP_ConnectStream(RTMP *r, int seekTime)
{
  RTMPPacket packet = { 0 };

  /* seekTime was already set by SetupStream / SetupURL.
   * This is only needed by ReconnectStream.
   */
  if (seekTime > 0)
    r->Link.seekTime = seekTime;

  r->m_mediaChannel = 0;

  while (!r->m_bPlaying && RTMP_IsConnected(r) && RTMP_ReadPacket(r, &packet))
    {
      if (RTMPPacket_IsReady(&packet))
	{
	  if (!packet.m_nBodySize)
	    continue;
	  if ((packet.m_packetType == RTMP_PACKET_TYPE_AUDIO) ||
	      (packet.m_packetType == RTMP_PACKET_TYPE_VIDEO) ||
	      (packet.m_packetType == RTMP_PACKET_TYPE_INFO))
	    {
	      RTMP_Log(RTMP_LOGWARNING, "Received FLV packet before play()! Ignoring.");
	      RTMPPacket_Free(&packet);
	      continue;
	    }
	  //处理Packet!
	  //----------------
	  r->dlg->AppendCInfo("建立网络流:处理收到的数据。开始处理收到的数据");
	  //-----------------------------
	  RTMP_ClientPacket(r, &packet);
	  //----------------
	  r->dlg->AppendCInfo("建立网络流:处理收到的数据。处理完毕,清除数据。");
	  //-----------------------------
	  RTMPPacket_Free(&packet);
	}
    }

  return r->m_bPlaying;
}

乍一看,这个函数的代码量好像挺少的,实际上不然,其复杂度还是挺高的。我觉得比RTMP_Connect()要复杂不少。

其关键就在于这个While()循环。首先,循环的三个条件都满足,就能进行循环。只有出错或者建立网络流(NetStream)的步骤完成后,才能跳出循环。

在这个函数中有两个函数尤为重要:

RTMP_ReadPacket()

RTMP_ClientPacket()

第一个函数的作用是读取通过Socket接收下来的消息(Message)包,但是不做任何处理。第二个函数则是处理消息(Message),并做出响应。这两个函数结合,就可以完成接收消息然后响应消息的步骤。

下面来开一下RTMP_ReadPacket():

//读取收下来的Chunk
int
RTMP_ReadPacket(RTMP *r, RTMPPacket *packet)
{
	//packet 存读取完后的的数据
	//Chunk Header最大值18
  uint8_t hbuf[RTMP_MAX_HEADER_SIZE] = { 0 };
	//header 指向的是从Socket中收下来的数据
  char *header = (char *)hbuf;
  int nSize, hSize, nToRead, nChunk;
  int didAlloc = FALSE;

  RTMP_Log(RTMP_LOGDEBUG2, "%s: fd=%d", __FUNCTION__, r->m_sb.sb_socket);
  //收下来的数据存入hbuf
  if (ReadN(r, (char *)hbuf, 1) == 0)
    {
      RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet header", __FUNCTION__);
      return FALSE;
    }
  //块类型fmt
  packet->m_headerType = (hbuf[0] & 0xc0) >> 6;
  //块流ID(2-63)
  packet->m_nChannel = (hbuf[0] & 0x3f);
  header++;
  //块流ID第1字节为0时,块流ID占2个字节
  if (packet->m_nChannel == 0)
    {
      if (ReadN(r, (char *)&hbuf[1], 1) != 1)
	{
	  RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet header 2nd byte",
	      __FUNCTION__);
	  return FALSE;
	}
	  //计算块流ID(64-319)
      packet->m_nChannel = hbuf[1];
      packet->m_nChannel += 64;
      header++;
    }
  //块流ID第1字节为0时,块流ID占3个字节
  else if (packet->m_nChannel == 1)
    {
      int tmp;
      if (ReadN(r, (char *)&hbuf[1], 2) != 2)
	{
	  RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet header 3nd byte",
	      __FUNCTION__);
	  return FALSE;
	}
      tmp = (hbuf[2] << 8) + hbuf[1];
	  //计算块流ID(64-65599)
      packet->m_nChannel = tmp + 64;
      RTMP_Log(RTMP_LOGDEBUG, "%s, m_nChannel: %0x", __FUNCTION__, packet->m_nChannel);
      header += 2;
    }
  //ChunkHeader的大小(4种)
  nSize = packetSize[packet->m_headerType];

  if (nSize == RTMP_LARGE_HEADER_SIZE)	/* if we get a full header the timestamp is absolute */
    packet->m_hasAbsTimestamp = TRUE;	//11字节的完整ChunkMsgHeader的TimeStamp是绝对值

  else if (nSize < RTMP_LARGE_HEADER_SIZE)
    {				/* using values from the last message of this channel */
      if (r->m_vecChannelsIn[packet->m_nChannel])
	memcpy(packet, r->m_vecChannelsIn[packet->m_nChannel],
	       sizeof(RTMPPacket));
    }

  nSize--;

  if (nSize > 0 && ReadN(r, header, nSize) != nSize)
    {
      RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet header. type: %x",
	  __FUNCTION__, (unsigned int)hbuf[0]);
      return FALSE;
    }

  hSize = nSize + (header - (char *)hbuf);

  if (nSize >= 3)
    {
	//TimeStamp(注意 BigEndian to SmallEndian)(11,7,3字节首部都有)
      packet->m_nTimeStamp = AMF_DecodeInt24(header);

      /*RTMP_Log(RTMP_LOGDEBUG, "%s, reading RTMP packet chunk on channel %x, headersz %i, timestamp %i, abs timestamp %i", __FUNCTION__, packet.m_nChannel, nSize, packet.m_nTimeStamp, packet.m_hasAbsTimestamp); */
	//消息长度(11,7字节首部都有)
      if (nSize >= 6)
	{
	  packet->m_nBodySize = AMF_DecodeInt24(header + 3);
	  packet->m_nBytesRead = 0;
	  RTMPPacket_Free(packet);
	//(11,7字节首部都有)
	  if (nSize > 6)
	    {
		  //Msg type ID
	      packet->m_packetType = header[6];
		  //Msg Stream ID
	      if (nSize == 11)
		packet->m_nInfoField2 = DecodeInt32LE(header + 7);
	    }
	}
	  //Extend TimeStamp
      if (packet->m_nTimeStamp == 0xffffff)
	{
	  if (ReadN(r, header + nSize, 4) != 4)
	    {
	      RTMP_Log(RTMP_LOGERROR, "%s, failed to read extended timestamp",
		  __FUNCTION__);
	      return FALSE;
	    }
	  packet->m_nTimeStamp = AMF_DecodeInt32(header + nSize);
	  hSize += 4;
	}
    }

  RTMP_LogHexString(RTMP_LOGDEBUG2, (uint8_t *)hbuf, hSize);

  if (packet->m_nBodySize > 0 && packet->m_body == NULL)
    {
      if (!RTMPPacket_Alloc(packet, packet->m_nBodySize))
	{
	  RTMP_Log(RTMP_LOGDEBUG, "%s, failed to allocate packet", __FUNCTION__);
	  return FALSE;
	}
      didAlloc = TRUE;
      packet->m_headerType = (hbuf[0] & 0xc0) >> 6;
    }

  nToRead = packet->m_nBodySize - packet->m_nBytesRead;
  nChunk = r->m_inChunkSize;
  if (nToRead < nChunk)
    nChunk = nToRead;

  /* Does the caller want the raw chunk? */
  if (packet->m_chunk)
    {
      packet->m_chunk->c_headerSize = hSize;
      memcpy(packet->m_chunk->c_header, hbuf, hSize);
      packet->m_chunk->c_chunk = packet->m_body + packet->m_nBytesRead;
      packet->m_chunk->c_chunkSize = nChunk;
    }

  if (ReadN(r, packet->m_body + packet->m_nBytesRead, nChunk) != nChunk)
    {
      RTMP_Log(RTMP_LOGERROR, "%s, failed to read RTMP packet body. len: %lu",
	  __FUNCTION__, packet->m_nBodySize);
      return FALSE;
    }

  RTMP_LogHexString(RTMP_LOGDEBUG2, (uint8_t *)packet->m_body + packet->m_nBytesRead, nChunk);

  packet->m_nBytesRead += nChunk;

  /* keep the packet as ref for other packets on this channel */
  if (!r->m_vecChannelsIn[packet->m_nChannel])
    r->m_vecChannelsIn[packet->m_nChannel] = (RTMPPacket *) malloc(sizeof(RTMPPacket));
  memcpy(r->m_vecChannelsIn[packet->m_nChannel], packet, sizeof(RTMPPacket));
  //读取完毕
  if (RTMPPacket_IsReady(packet))
    {
      /* make packet's timestamp absolute */
      if (!packet->m_hasAbsTimestamp)
	packet->m_nTimeStamp += r->m_channelTimestamp[packet->m_nChannel];	/* timestamps seem to be always relative!! */

      r->m_channelTimestamp[packet->m_nChannel] = packet->m_nTimeStamp;

      /* reset the data from the stored packet. we keep the header since we may use it later if a new packet for this channel */
      /* arrives and requests to re-use some info (small packet header) */
      r->m_vecChannelsIn[packet->m_nChannel]->m_body = NULL;
      r->m_vecChannelsIn[packet->m_nChannel]->m_nBytesRead = 0;
      r->m_vecChannelsIn[packet->m_nChannel]->m_hasAbsTimestamp = FALSE;	/* can only be false if we reuse header */
    }
  else
    {
      packet->m_body = NULL;	/* so it won't be erased on free */
    }

  return TRUE;
}

在这里要注意的是,接收下来的实际上是块(Chunk)而不是消息(Message),因为消息(Message)在网络上传播的时候,实际上要分割成块(Chunk)。

这里解析的就是块(Chunk)

可参考:RTMP规范简单分析

具体的解析代码我就不多说了,直接参考RTMP协议规范就可以了,一个字节一个字节的解析就OK了。

rtmpdump源代码(Linux):http://download.csdn.net/detail/leixiaohua1020/6376561

rtmpdump源代码(VC 2005 工程):http://download.csdn.net/detail/leixiaohua1020/6563163

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