RTMPdump（libRTMP） 源代码分析 9： 接收消息（Message）（接收视音频数据）(二)
pos, nRead);
r->m_read.buflen -= nRead;
if (!r->m_read.buflen)
{
free(r->m_read.buf);
r->m_read.buf = NULL;
r->m_read.bufpos = NULL;
}
else
{
r->m_read.bufpos += nRead;
}
buf += nRead;
total += nRead;
size -= nRead;
}
//接着读
while (size > 0 && (nRead = Read_1_Packet(r, buf, size)) >= 0)
{
if (!nRead) continue;
buf += nRead;
total += nRead;
size -= nRead;
break;
}
if (nRead < 0)
r->m_read.status = nRead;
if (size < 0)
total += size;
return total;
}
程序关键的地方都已经注释上了代码，在此就不重复说明了。有一点要提一下：RTMP传送的视音频数据的格式和FLV（FLash Video）格式是一样的，把接收下来的数据直接存入文件就可以了。但是这些视音频数据没有文件头，是纯视音频数据，因此需要在其前面加上FLV格式的文件头，这样得到的数据存成文件后才能被一般的视频播放器所播放。FLV格式的文件头是13个字节，如代码中所示。
RTMP_Read()中实际读取数据的函数是Read_1_Packet()，它的功能是从网络上读取一个RTMPPacket的数据，来看看它的源代码吧：
[cpp]
/* 从流媒体中读取多媒体packet。
* Returns -3 if Play.Close/Stop, -2 if fatal error, -1 if no more media
* packets, 0 if ignorable error, >0 if there is a media packet
*/
static int
Read_1_Packet(RTMP *r, char *buf, unsigned int buflen)
{
uint32_t prevTagSize = 0;
int rtnGetNextMediaPacket = 0, ret = RTMP_READ_EOF;
RTMPPacket packet = { 0 };
int recopy = FALSE;
unsigned int size;
char *ptr, *pend;
uint32_t nTimeStamp = 0;
unsigned int len;
//获取下一个packet
rtnGetNextMediaPacket = RTMP_GetNextMediaPacket(r, &packet);
while (rtnGetNextMediaPacket)
{
char *packetBody = packet.m_body;
unsigned int nPacketLen = packet.m_nBodySize;
/* Return -3 if this was completed nicely with invoke message
* Play.Stop or Play.Complete
*/
if (rtnGetNextMediaPacket == 2)
{
RTMP_Log(RTMP_LOGDEBUG,
"Got Play.Complete or Play.Stop from server. "
"Assuming stream is complete");
ret = RTMP_READ_COMPLETE;
break;
}
//设置dataType
r->m_read.dataType |= (((packet.m_packetType == 0x08) << 2) |
(packet.m_packetType == 0x09));
//MessageID为9时，为视频数据，数据太小时。。。
if (packet.m_packetType == 0x09 && nPacketLen <= 5)
{
RTMP_Log(RTMP_LOGDEBUG, "ignoring too small video packet: size: %d",
nPacketLen);
ret = RTMP_READ_IGNORE;
break;
}
//MessageID为8时，为音频数据，数据太小时。。。
if (packet.m_packetType == 0x08 && nPacketLen <= 1)
{
RTMP_Log(RTMP_LOGDEBUG, "ignoring too small audio packet: size: %d",
nPacketLen);
ret = RTMP_READ_IGNORE;
break;
}
if (r->m_read.flags & RTMP_READ_SEEKING)
{
ret = RTMP_READ_IGNORE;
break;
}
#ifdef _DEBUG
RTMP_Log(RTMP_LOGDEBUG, "type: %02X, size: %d, TS: %d ms, abs TS: %d",
packet.m_packetType, nPacketLen, packet.m_nTimeStamp,
packet.m_hasAbsTimestamp);
if (packet.m_packetType == 0x09)
RTMP_Log(RTMP_LOGDEBUG, "frametype: %02X", (*packetBody & 0xf0));
#endif
if (r->m_read.flags & RTMP_READ_RESUME)
{
/* check the header if we get one */
//此类packet的timestamp都是0
if (packet.m_nTimeStamp == 0)
{
//messageID=18，数据消息（AMF0）
if (r->m_read.nMetaHeaderSize > 0
&& packet.m_pa