• live555 rtsp服务器实战之createNewStreamSource

    live555关于RTSP协议交互流程

    live555的核心数据结构值之闭环双向链表

    live555 rtsp服务器实战之createNewStreamSource

    live555搭建实时播放rtsp服务器

    live555 rtsp服务器实战之doGetNextFrame

    概述

            live555用于实际项目开发时，createNewStreamSource和doGetNextFrame是必须要实现的两个虚函数，一般会创建两个类来实现这两个函数：假如这两个类为H264LiveVideoServerMediaSubssion和H264FramedLiveSource；       

            H264LiveVideoServerMediaSubssion为实时视频会话类，用于实现createNewStreamSource虚函数；

            H264FramedLiveSource为实时视频帧资源类，用户实现doGetNextFrame函数；

            那么这两个函数是什么时候被调用以及他们的作用是什么呢？本节将详细介绍；

    声明：该文章基于H264视频源为基础分析，其他源类似；

            由于这两个类主要是自定义虚函数，所以存在一定的继承关系，首先需要明确这两个类的继承关系(本章只介绍H264LiveVideoServerMediaSubssion)：

            H264LiveVideoServerMediaSubssion:OnDemandServerMediaSubsession:ServerMediaSubsession:Medium

    createNewStreamSource

    本章介绍createNewStreamSource函数；

            虚函数createNewStreamSource声明于OnDemandServerMediaSubsession类：

    1. virtual FramedSource* createNewStreamSource(unsigned clientSessionId,
    2.                 unsigned& estBitrate) = 0;

            可以看出声明时为纯虚函数（live555提供的对外接口，用户自定义实现），必须有子类对该函数进行实现；该函数用于获取媒体流源的资源对象，简单点说就是指明服务器调用哪个doGetNextFrame函数获取视频流；

            因此H264LiveVideoServerMediaSubssion类需要继承OnDemandServerMediaSubsession类；

            createNewStreamSource函数实现解析：

    1. FramedSource* H264LiveVideoServerMediaSubssion::createNewStreamSource(unsigned clientSessionId, unsigned& estBitrate)
    2. {
    3.     /* Remain to do : assign estBitrate */
    4.     estBitrate = 1000; // kbps, estimate
    5.  
    6.     //创建视频源
    7.     H264FramedLiveSource* liveSource = H264FramedLiveSource::createNew(envir(), Server_datasize, Server_databuf, Server_dosent);
    8.     if (liveSource == NULL)
    9.     {
    10.         return NULL;
    11.     }
    12.  
    13.     // Create a framer for the Video Elementary Stream:
    14.     return H264VideoStreamFramer::createNew(envir(), liveSource);
    15. }

            上述代码就是最基础的虚函数createNewStreamSource的实现，其中H264FramedLiveSource就是视频源资源的类；也就是获取视频帧的函数doGetNextFrame所在的类；该函数主要做了两件事：

    1. 创建h264帧资源类对象liveSource；目的是获取调用doGetNextFrame的方法；

    2. 返回H264VideoStreamFramer类对象，并将h264帧资源类对象传递进去，最终liveSource赋值给StreamParser类中成员变量fInputSource和FramedFilter类的成员变量fInputSource；

            该函数在SETUP信令交互时期被调用，首先看一下信令处理函数handleRequestBytes：

    1. void RTSPServer::RTSPClientConnection::handleRequestBytes(int newBytesRead)
    2. {
    3.     .
    4.     .
    5.     .
    6.     if (urlIsRTSPS != fOurRTSPServer.fOurConnectionsUseTLS)
    7.       {
    8. #ifdef DEBUG
    9.         fprintf(stderr, "Calling handleCmd_redirect()\n");
    10. #endif
    11.         handleCmd_redirect(urlSuffix);
    12.       }
    13.       else if (strcmp(cmdName, "OPTIONS") == 0)
    14.       {
    15.         // If the "OPTIONS" command included a "Session:" id for a session that doesn't exist,
    16.         // then treat this as an error:
    17.         if (requestIncludedSessionId && clientSession == NULL)
    18.         {
    19. #ifdef DEBUG
    20.           fprintf(stderr, "Calling handleCmd_sessionNotFound() (case 1)\n");
    21. #endif
    22.           handleCmd_sessionNotFound();
    23.         }
    24.         else
    25.         {
    26.           // Normal case:
    27.           handleCmd_OPTIONS();
    28.         }
    29.       }
    30.       else if (urlPreSuffix[0] == '\0' && urlSuffix[0] == '*' && urlSuffix[1] == '\0')
    31.       {
    32.         // The special "*" URL means: an operation on the entire server.  This works only for GET_PARAMETER and SET_PARAMETER:
    33.         if (strcmp(cmdName, "GET_PARAMETER") == 0)
    34.         {
    35.           handleCmd_GET_PARAMETER((char const *)fRequestBuffer);
    36.         }
    37.         else if (strcmp(cmdName, "SET_PARAMETER") == 0)
    38.         {
    39.           handleCmd_SET_PARAMETER((char const *)fRequestBuffer);
    40.         }
    41.         else
    42.         {
    43.           handleCmd_notSupported();
    44.         }
    45.       }
    46.       else if (strcmp(cmdName, "DESCRIBE") == 0)
    47.       {
    48.         handleCmd_DESCRIBE(urlPreSuffix, urlSuffix, (char const *)fRequestBuffer);
    49.       }
    50.       else if (strcmp(cmdName, "SETUP") == 0)
    51.       {
    52.         Boolean areAuthenticated = True;
    53.  
    54.         if (!requestIncludedSessionId)
    55.         {
    56.           // No session id was present in the request.
    57.           // So create a new "RTSPClientSession" object for this request.
    58.  
    59.           // But first, make sure that we're authenticated to perform this command:
    60.           char urlTotalSuffix[2 * RTSP_PARAM_STRING_MAX];
    61.           // enough space for urlPreSuffix/urlSuffix'\0'
    62.           urlTotalSuffix[0] = '\0';
    63.           if (urlPreSuffix[0] != '\0')
    64.           {
    65.             strcat(urlTotalSuffix, urlPreSuffix);
    66.             strcat(urlTotalSuffix, "/");
    67.           }
    68.           strcat(urlTotalSuffix, urlSuffix);
    69.           if (authenticationOK("SETUP", urlTotalSuffix, (char const *)fRequestBuffer))
    70.           {
    71.             clientSession = (RTSPServer::RTSPClientSession *)fOurRTSPServer.createNewClientSessionWithId();
    72.           }
    73.           else
    74.           {
    75.             areAuthenticated = False;
    76.           }
    77.         }
    78.         if (clientSession != NULL)
    79.         {
    80.           clientSession->handleCmd_SETUP(this, urlPreSuffix, urlSuffix, (char const *)fRequestBuffer);
    81.           playAfterSetup = clientSession->fStreamAfterSETUP;
    82.         }
    83.         else if (areAuthenticated)
    84.         {
    85. #ifdef DEBUG
    86.           fprintf(stderr, "Calling handleCmd_sessionNotFound() (case 2)\n");
    87. #endif
    88.           handleCmd_sessionNotFound();
    89.         }
    90.       }
    91.       else if (strcmp(cmdName, "TEARDOWN") == 0 || strcmp(cmdName, "PLAY") == 0 || strcmp(cmdName, "PAUSE") == 0 || strcmp(cmdName, "GET_PARAMETER") == 0 || strcmp(cmdName, "SET_PARAMETER") == 0)
    92.       {
    93.         if (clientSession != NULL)
    94.         {
    95.           clientSession->handleCmd_withinSession(this, cmdName, urlPreSuffix, urlSuffix, (char const *)fRequestBuffer);
    96.         }
    97.         else
    98.         {
    99. #ifdef DEBUG
    100.           fprintf(stderr, "Calling handleCmd_sessionNotFound() (case 3)\n");
    101. #endif
    102.           handleCmd_sessionNotFound();
    103.         }
    104.       }
    105.       else if (strcmp(cmdName, "REGISTER") == 0 || strcmp(cmdName, "DEREGISTER") == 0)
    106.       {
    107.         // Because - unlike other commands - an implementation of this command needs
    108.         // the entire URL, we re-parse the command to get it:
    109.         char *url = strDupSize((char *)fRequestBuffer);
    110.         if (sscanf((char *)fRequestBuffer, "%*s %s", url) == 1)
    111.         {
    112.           // Check for special command-specific parameters in a "Transport:" header:
    113.           Boolean reuseConnection, deliverViaTCP;
    114.           char *proxyURLSuffix;
    115.           parseTransportHeaderForREGISTER((const char *)fRequestBuffer, reuseConnection, deliverViaTCP, proxyURLSuffix);
    116.  
    117.           handleCmd_REGISTER(cmdName, url, urlSuffix, (char const *)fRequestBuffer, reuseConnection, deliverViaTCP, proxyURLSuffix);
    118.           delete[] proxyURLSuffix;
    119.         }
    120.         else
    121.         {
    122.           handleCmd_bad();
    123.         }
    124.         delete[] url;
    125.       }
    126.       else
    127.       {
    128.         // The command is one that we don't handle:
    129.         handleCmd_notSupported();
    130.       }
    131.       .
    132.       .
    133.       .
    134. }

            handleRequestBytes函数是在doEventLoop主循环中监测的RTSP客户端有数据发送时调用的函数(关于rtsp的tcp udp协议交互，参考上面的文章)，作用就是处理各种信令(OPTION DESCRIBE SETUP等)及数据；其中就调用了handleCmd_SETUP处理SETUP信令的函数；handleCmd_SETUP函数又调用了getStreamParameters函数：

    1. void OnDemandServerMediaSubsession ::getStreamParameters(unsigned clientSessionId,
    2.                                                          struct sockaddr_storage const &clientAddress,
    3.                                                          Port const &clientRTPPort,
    4.                                                          Port const &clientRTCPPort,
    5.                                                          int tcpSocketNum,
    6.                                                          unsigned char rtpChannelId,
    7.                                                          unsigned char rtcpChannelId,
    8.                                                          TLSState *tlsState,
    9.                                                          struct sockaddr_storage &destinationAddress,
    10.                                                          u_int8_t & /*destinationTTL*/,
    11.                                                          Boolean &isMulticast,
    12.                                                          Port &serverRTPPort,
    13.                                                          Port &serverRTCPPort,
    14.                                                          void *&streamToken)
    15. {
    16.     if (addressIsNull(destinationAddress))
    17.     {
    18.         // normal case - use the client address as the destination address:
    19.         destinationAddress = clientAddress;
    20.     }
    21.   isMulticast = False;
    22.  
    23.   if (fLastStreamToken != NULL && fReuseFirstSource)
    24.   {
    25.     // Special case: Rather than creating a new 'StreamState',
    26.     // we reuse the one that we've already created:
    27.     serverRTPPort = ((StreamState *)fLastStreamToken)->serverRTPPort();
    28.     serverRTCPPort = ((StreamState *)fLastStreamToken)->serverRTCPPort();
    29.     ++((StreamState *)fLastStreamToken)->referenceCount();
    30.     streamToken = fLastStreamToken;
    31.   }
    32.   else
    33.   {
    34.     // Normal case: Create a new media source:
    35.     unsigned streamBitrate;
    36.     FramedSource *mediaSource = createNewStreamSource(clientSessionId, streamBitrate);
    37.     .
    38.     .
    39.     .
    40.   }
    41.   .
    42.   .
    43.   .
    44. }

            该函数就在OnDemandServerMediaSubsession类，也就是createNewStreamSource实现类H264LiveVideoServerMediaSubssion的父类，这时调用的createNewStreamSource就是我们自己实现的逻辑啦！返回值mediaSource后续被用来调用doGetNextFrame函数获取视频帧使用！

            可以看出这两件事的目的都是为了告诉rtsp服务器怎么获取视频帧数据；关于fInputSource变量什么时候被使用的，请参考我的下篇文章：未知地址！哈哈哈！

            下节的doGetNextFrame分析才是重点，敬请期待！

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  • 原文地址：https://blog.csdn.net/qq_39466755/article/details/140438101