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RTMP协议相关：
【流媒体】RTMP协议概述
【流媒体】RTMP协议的数据格式
【流媒体】RTMP协议的消息类型
【流媒体】RTMPDump—主流程简单分析
【流媒体】RTMPDump—RTMP_Connect函数（握手、网络连接）
【流媒体】RTMPDump—RTMP_ConnectStream（创建流连接）
【流媒体】RTMPDump—Download（接收流媒体信息）
【流媒体】RTMPDump—AMF编码
【流媒体】基于libRTMP的H264推流器

参考雷博的系列文章（可以从一篇链接到其他文章）：
RTMPdump 源代码分析 1： main()函数

在进行流连接之后，还可以进行传输过来数据的下载，执行这一功能的函数是Download()，其中使用RTMP_Read()读取数据，随后使用fwrite写入文件。写入文件通常是FLV格式，如果没有指定这个file，则会默认写到stdout

int
Download(RTMP * rtmp,		// connected RTMP objectFILE * file, uint32_t dSeek, uint32_t dStopOffset, double duration, int bResume, char* metaHeader, uint32_t nMetaHeaderSize, char* initialFrame, int initialFrameType, uint32_t nInitialFrameSize, int nSkipKeyFrames, int bStdoutMode, int bLiveStream, int bRealtimeStream, int bHashes, int bOverrideBufferTime, uint32_t bufferTime, double* percent)	// percentage downloaded [out]
{int32_t now, lastUpdate;int bufferSize = 64 * 1024;char* buffer;int nRead = 0;off_t size = ftello(file);unsigned long lastPercent = 0;rtmp->m_read.timestamp = dSeek;*percent = 0.0;if (rtmp->m_read.timestamp){RTMP_Log(RTMP_LOGDEBUG, "Continuing at TS: %d ms\n", rtmp->m_read.timestamp);}if (bLiveStream){RTMP_LogPrintf("Starting Live Stream\n");}else{// print initial status// Workaround to exit with 0 if the file is fully (> 99.9%) downloadedif (duration > 0){if ((double)rtmp->m_read.timestamp >= (double)duration * 999.0){RTMP_LogPrintf("Already Completed at: %.3f sec Duration=%.3f sec\n",(double)rtmp->m_read.timestamp / 1000.0,(double)duration / 1000.0);return RD_SUCCESS;}else{*percent = ((double)rtmp->m_read.timestamp) / (duration * 1000.0) * 100.0;*percent = ((double)(int)(*percent * 10.0)) / 10.0;RTMP_LogPrintf("%s download at: %.3f kB / %.3f sec (%.1f%%)\n",bResume ? "Resuming" : "Starting",(double)size / 1024.0, (double)rtmp->m_read.timestamp / 1000.0,*percent);}}else{RTMP_LogPrintf("%s download at: %.3f kB\n",bResume ? "Resuming" : "Starting",(double)size / 1024.0);}if (bRealtimeStream)RTMP_LogPrintf("  in approximately realtime (disabled BUFX speedup hack)\n");}if (dStopOffset > 0)RTMP_LogPrintf("For duration: %.3f sec\n", (double)(dStopOffset - dSeek) / 1000.0);if (bResume && nInitialFrameSize > 0)rtmp->m_read.flags |= RTMP_READ_RESUME;rtmp->m_read.initialFrameType = initialFrameType;rtmp->m_read.nResumeTS = dSeek;rtmp->m_read.metaHeader = metaHeader;rtmp->m_read.initialFrame = initialFrame;rtmp->m_read.nMetaHeaderSize = nMetaHeaderSize;rtmp->m_read.nInitialFrameSize = nInitialFrameSize;buffer = (char*)malloc(bufferSize);now = RTMP_GetTime();lastUpdate = now - 1000;do{// 读取信息nRead = RTMP_Read(rtmp, buffer, bufferSize);//RTMP_LogPrintf("nRead: %d\n", nRead);if (nRead > 0){// 将数据写入到file当中，FLV格式// 如果这个file没有指定，默认是stdoutif (fwrite(buffer, sizeof(unsigned char), nRead, file) !=(size_t)nRead){RTMP_Log(RTMP_LOGERROR, "%s: Failed writing, exiting!", __FUNCTION__);free(buffer);return RD_FAILED;}size += nRead;//RTMP_LogPrintf("write %dbytes (%.1f kB)\n", nRead, nRead/1024.0);if (duration <= 0)	// if duration unknown try to get it from the stream (onMetaData)duration = RTMP_GetDuration(rtmp);if (duration > 0){// make sure we claim to have enough buffer time!if (!bOverrideBufferTime && bufferTime < (duration * 1000.0)){bufferTime = (uint32_t)(duration * 1000.0) + 5000;	// extra 5sec to make sure we've got enoughRTMP_Log(RTMP_LOGDEBUG,"Detected that buffer time is less than duration, resetting to: %dms",bufferTime);RTMP_SetBufferMS(rtmp, bufferTime);RTMP_UpdateBufferMS(rtmp);}*percent = ((double)rtmp->m_read.timestamp) / (duration * 1000.0) * 100.0;*percent = ((double)(int)(*percent * 10.0)) / 10.0;if (bHashes){if (lastPercent + 1 <= *percent){RTMP_LogStatus("#");lastPercent = (unsigned long)* percent;}}else{now = RTMP_GetTime();if (abs(now - lastUpdate) > 200){RTMP_LogStatus("\r%.3f kB / %.2f sec (%.1f%%)",(double)size / 1024.0,(double)(rtmp->m_read.timestamp) / 1000.0, *percent);lastUpdate = now;}}}else{now = RTMP_GetTime();if (abs(now - lastUpdate) > 200){if (bHashes)RTMP_LogStatus("#");elseRTMP_LogStatus("\r%.3f kB / %.2f sec", (double)size / 1024.0,(double)(rtmp->m_read.timestamp) / 1000.0);lastUpdate = now;}}}else{
#ifdef _DEBUGRTMP_Log(RTMP_LOGDEBUG, "zero read!");
#endifif (rtmp->m_read.status == RTMP_READ_EOF)break;}} while (!RTMP_ctrlC && nRead > -1 && RTMP_IsConnected(rtmp) && !RTMP_IsTimedout(rtmp));free(buffer);if (nRead < 0)nRead = rtmp->m_read.status;/* Final status update */if (!bHashes){if (duration > 0){*percent = ((double)rtmp->m_read.timestamp) / (duration * 1000.0) * 100.0;*percent = ((double)(int)(*percent * 10.0)) / 10.0;RTMP_LogStatus("\r%.3f kB / %.2f sec (%.1f%%)",(double)size / 1024.0,(double)(rtmp->m_read.timestamp) / 1000.0, *percent);}else{RTMP_LogStatus("\r%.3f kB / %.2f sec", (double)size / 1024.0,(double)(rtmp->m_read.timestamp) / 1000.0);}}RTMP_Log(RTMP_LOGDEBUG, "RTMP_Read returned: %d", nRead);if (bResume && nRead == -2){RTMP_LogPrintf("Couldn't resume FLV file, try --skip %d\n\n",nSkipKeyFrames + 1);return RD_FAILED;}if (nRead == -3)return RD_SUCCESS;if ((duration > 0 && *percent < 99.9) || RTMP_ctrlC || nRead < 0|| RTMP_IsTimedout(rtmp)){return RD_INCOMPLETE;}return RD_SUCCESS;
}