live555源码分析（八）多播

喜欢ヅ旅行 2024-04-18 21:10 82阅读 0赞

**live555源码分析系列**

[live555源码分析（一）live555初体验][live555_live555]

[live555源码分析（二）基本组件上][live555]

[live555源码分析（三）基本组件下][live555 1]

[live555源码分析（四）RTSPServer分析][live555_RTSPServer]

[live555源码分析（五）DESCRIBE请求的处理][live555_DESCRIBE]

[live555源码分析（六）SETUP和PLAY请求的处理][live555_SETUP_PLAY]

[live555源码分析（七）播放过程][live555 2]

[live555源码分析（八）多播][live555 3]

# live555源码分析（八）多播 #

### 文章目录 ###

*  live555源码分析（八）多播
 *   *  一、单播与多播实现区别
     *  二、多播示例注解
     *  三、PassiveServerMediaSubsession分析

## 一、单播与多播实现区别 ##

前面的例子实现的是单播的情况，其实多播也是差不多的，主要区别在于子会话的实现不同

在live555中，单播的子会话是继承于`OnDemandServerMediaSubsession`的，多播是使用`PassiveServerMediaSubsession`

单播与多播的主要区别在于开始播放后，会不会把客户端目的添加到发送目标中

单播会将每个客户端目的添加到发送目标中，而多播的发送目标只有多播地址

`OnDemandServerMediaSubsession::startStream`会将客户端目的添加到发送目标中

而`PassiveServerMediaSubsession::startStream`并不会

## 二、多播示例注解 ##

在live555中的`testProgs\testH264VideoStreamer.cpp`实现了一个多播H.264文件的例子

如果有仔细阅读前几篇文章，那么这个示例应该很容易看懂，本文将对这个示例进行注解，然后分析`PassiveServerMediaSubsession`

#include <liveMedia.hh>
    #include <BasicUsageEnvironment.hh>
    #include <GroupsockHelper.hh>
    
    UsageEnvironment* env;
    char const* inputFileName = "test.264";
    H264VideoStreamFramer* videoSource;
    RTPSink* videoSink;
    
    void play();
    
    int main(int argc, char** argv) {
      TaskScheduler* scheduler = BasicTaskScheduler::createNew(); // 调度器
      env = BasicUsageEnvironment::createNew(*scheduler); // 环境变量
    
      /* 随机产生多播地址 */
      struct in_addr destinationAddress;
      destinationAddress.s_addr = chooseRandomIPv4SSMAddress(*env);
    
      /* 指定多播的RTP和RTCP端口 */
      const unsigned short rtpPortNum = 18888;
      const unsigned short rtcpPortNum = rtpPortNum+1;
      const unsigned char ttl = 255;
      const Port rtpPort(rtpPortNum);
      const Port rtcpPort(rtcpPortNum);
    
      Groupsock rtpGroupsock(*env, destinationAddress, rtpPort, ttl);
      rtpGroupsock.multicastSendOnly();
      Groupsock rtcpGroupsock(*env, destinationAddress, rtcpPort, ttl);
      rtcpGroupsock.multicastSendOnly();
    
    
      OutPacketBuffer::maxSize = 100000;
    
      /* 创建消费者，用于处理和发送H264的NALU */
      videoSink = H264VideoRTPSink::createNew(*env, &rtpGroupsock, 96);
    
      /* 创建RTCP */
      const unsigned estimatedSessionBandwidth = 500;
      const unsigned maxCNAMElen = 100;
      unsigned char CNAME[maxCNAMElen+1];
      gethostname((char*)CNAME, maxCNAMElen);
      CNAME[maxCNAMElen] = '\0';
      RTCPInstance* rtcp
      = RTCPInstance::createNew(*env, &rtcpGroupsock,
    			    estimatedSessionBandwidth, CNAME,
    			    videoSink, NULL,
    			    True /* 多播 */);
      
      /* 创建RTSP服务器，指定端口8554 */
      RTSPServer* rtspServer = RTSPServer::createNew(*env, 8554);
      if (rtspServer == NULL) {
        *env << "Failed to create RTSP server: " << env->getResultMsg() << "\n";
        exit(1);
      }
    
      /* 创建一个会话 */
      ServerMediaSession* sms
        = ServerMediaSession::createNew(*env, "testStream", inputFileName,
    		   "Session streamed by \"testH264VideoStreamer\"",
    					   True /*SSM，此位表示是否为多播*/);
    					   
      /* 添加子会话，子会话为H.264视频流 */
      sms->addSubsession(PassiveServerMediaSubsession::createNew(*videoSink, rtcp));
      rtspServer->addServerMediaSession(sms); // 将会话添加到会话中
    
      /* 打印会话的url */
      char* url = rtspServer->rtspURL(sms);
      *env << "Play this stream using the URL \"" << url << "\"\n";
      delete[] url;
    
      /* 开始播放 */
      *env << "Beginning streaming...\n";
      play();
    
      /* 开始事件循环 */
      env->taskScheduler().doEventLoop();
    
      return 0;
    }
    
    /* 清除资源，重新播放 */
    void afterPlaying(void* /*clientData*/) {
      *env << "...done reading from file\n";
      videoSink->stopPlaying();
      Medium::close(videoSource);
    
      play();
    }
    
    void play() {
      /* 字节流读取文件 */
      ByteStreamFileSource* fileSource
        = ByteStreamFileSource::createNew(*env, inputFileName);
      if (fileSource == NULL) {
        *env << "Unable to open file \"" << inputFileName
             << "\" as a byte-stream file source\n";
        exit(1);
      }
    
      FramedSource* videoES = fileSource;
    
      /* 装饰者，读取NALU */
      videoSource = H264VideoStreamFramer::createNew(*env, videoES);
    
      *env << "Beginning to read from file...\n";
      /* 开始播放 */
      videoSink->startPlaying(*videoSource, afterPlaying, videoSink);
    }

## 三、PassiveServerMediaSubsession分析 ##

这里主要分析`getStreamParameters`函数还有`startStream`函数

`getStreamParameters`函数在DESCRIBE阶段被调用

`startStream`函数在PLAY阶段被调用

首先看`getStreamParameters`

void PassiveServerMediaSubsession
    ::getStreamParameters(unsigned clientSessionId,
    		      netAddressBits clientAddress,
    		      Port const& /*clientRTPPort*/,
    		      Port const& clientRTCPPort,
    		      int /*tcpSocketNum*/,
    		      unsigned char /*rtpChannelId*/,
    		      unsigned char /*rtcpChannelId*/,
    		      netAddressBits& destinationAddress,
    		      u_int8_t& destinationTTL,
    		      Boolean& isMulticast,
    		      Port& serverRTPPort,
    		      Port& serverRTCPPort,
    		      void*& streamToken) {
        /* 指定多播 */
        isMulticast = True;
     
        /* 服务端RTP和RTCP端口 */
        serverRTPPort = gs.port();
        serverRTCPPort = rtcpGS->port();
    	...
            
        /* 将客户端的RTCP保存下来 */
    	RTCPSourceRecord* source = new RTCPSourceRecord(clientAddress, clientRTCPPort);
        fClientRTCPSourceRecords->Add((char const*)clientSessionId, source);
    }

可以看到会指定当前会话为多播，并且返回服务端的RTP和RTCP端口，但没有将客户端目的添加到发送目标中

这里将客户端的RTCP保存下来的原因是，虽然发送是多播，但是RTCP信息的接收还是采用单播，所以要独立处理每一个RTCP的接收

下面看一看`startStream`的实现

void PassiveServerMediaSubsession::startStream() {
        RTCPSourceRecord* source = (RTCPSourceRecord*)(fClientRTCPSourceRecords->Lookup((char const*)clientSessionId));
        /* 指定RTCP的反射处理 */
        fRTCPInstance->setSpecificRRHandler(source->addr, source->port,
        						rtcpRRHandler, rtcpRRHandlerClientData);
    }

它设置了客户端RTCP的反射处理

live555源码分析系列的文章到这里就结束了，希望对live555的初学者有所帮助

[live555_live555]: https://blog.csdn.net/weixin_42462202/article/details/100626262
[live555]: https://blog.csdn.net/weixin_42462202/article/details/100677974
[live555 1]: https://blog.csdn.net/weixin_42462202/article/details/100709515
[live555_RTSPServer]: https://blog.csdn.net/weixin_42462202/article/details/100711104
[live555_DESCRIBE]: https://blog.csdn.net/weixin_42462202/article/details/100713429
[live555_SETUP_PLAY]: https://blog.csdn.net/weixin_42462202/article/details/100733866
[live555 2]: https://blog.csdn.net/weixin_42462202/article/details/100746999
[live555 3]: https://blog.csdn.net/weixin_42462202/article/details/100748292