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live555学习笔记－RTSP服务运作

 
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RTSP服务运作

基础基本搞明白了，那么RTSP,RTP等这些协议又是如何利用这些基础机制运作的呢？
首先来看RTSP.

RTSP首先需建立TCP侦听socket。可见于此函数：

[cpp]view plaincopy
 
  1. DynamicRTSPServer*DynamicRTSPServer::createNew(UsageEnvironment&env,PortourPort,
  2. UserAuthenticationDatabase*authDatabase,
  3. unsignedreclamationTestSeconds){
  4. intourSocket=setUpOurSocket(env,ourPort);//建立TCPsocket
  5. if(ourSocket==-1)
  6. returnNULL;
  9. returnnewDynamicRTSPServer(env,ourSocket,ourPort,authDatabase,
  10. reclamationTestSeconds);
  11. }


要帧听客户端的连接，就需要利用任务调度机制了，所以需添加一个socket handler。可见于此函数：

[cpp]view plaincopy
 
  1. RTSPServer::RTSPServer(UsageEnvironment&env,
  2. intourSocket,
  3. PortourPort,
  4. UserAuthenticationDatabase*authDatabase,
  5. unsignedreclamationTestSeconds):
  6. Medium(env),
  7. fRTSPServerSocket(ourSocket),
  8. fRTSPServerPort(ourPort),
  9. fHTTPServerSocket(-1),
  10. fHTTPServerPort(0),
  11. fClientSessionsForHTTPTunneling(NULL),
  12. fAuthDB(authDatabase),
  13. fReclamationTestSeconds(reclamationTestSeconds),
  14. fServerMediaSessions(HashTable::create(STRING_HASH_KEYS))
  15. {
  16. #ifdefUSE_SIGNALS
  17. //IgnoretheSIGPIPEsignal,sothatclientsonthesamehostthatarekilled
  18. //don'talsokillus:
  19. signal(SIGPIPE,SIG_IGN);
  20. #endif
  23. //Arrangetohandleconnectionsfromothers:
  24. env.taskScheduler().turnOnBackgroundReadHandling(
  25. fRTSPServerSocket,
  26. (TaskScheduler::BackgroundHandlerProc*)&incomingConnectionHandlerRTSP,
  27. this);
  28. }



当收到客户的连接时需保存下代表客户端的新socket，以后用这个socket与这个客户通讯。每个客户将来会对应一个rtp会话，而且各客户的RTSP请求只控制自己的rtp会话，那么最好建立一个会话类，代表各客户的rtsp会话。于是类RTSPServer::RTSPClientSession产生，它保存的代表客户的socket。下为RTSPClientSession的创建过程

 

[cpp]view plaincopy
 
  1. voidRTSPServer::incomingConnectionHandler(intserverSocket)
  2. {
  3. structsockaddr_inclientAddr;
  4. SOCKLEN_TclientAddrLen=sizeofclientAddr;
  6. //接受连接
  7. intclientSocket=accept(serverSocket,
  8. (structsockaddr*)&clientAddr,
  9. &clientAddrLen);
  11. if(clientSocket<0){
  12. interr=envir().getErrno();
  13. if(err!=EWOULDBLOCK){
  14. envir().setResultErrMsg("accept()failed:");
  15. }
  16. return;
  17. }
  19. //设置socket的参数
  20. makeSocketNonBlocking(clientSocket);
  21. increaseSendBufferTo(envir(),clientSocket,50*1024);
  23. #ifdefDEBUG
  24. envir()<<"accept()edconnectionfrom"<<our_inet_ntoa(clientAddr.sin_addr)<<"\n";
  25. #endif
  27. //产生一个sessonid
  29. //CreateanewobjectforthisRTSPsession.
  30. //(Choosearandom32-bitintegerforthesessionid(itwillbeencodedasa8-digithexnumber).Wedon'tbothercheckingfor
  31. //acollision;theprobabilityoftwoconcurrentsessionsgettingthesamesessionidisverylow.)
  32. //(Wedo,however,avoidchoosingsessionid0,becausethathasaspecialuse(by"OnDemandServerMediaSubsession").)
  33. unsignedsessionId;
  34. do{
  35. sessionId=(unsigned)our_random();
  36. }while(sessionId==0);
  38. //创建RTSPClientSession，注意传入的参数
  39. (void)createNewClientSession(sessionId,clientSocket,clientAddr);
  40. }

 

RTSPClientSession要提供什么功能呢？可以想象：需要监听客户端的rtsp请求并回应它，需要在DESCRIBE请求中返回所请求的流的信息，需要在SETUP请求中建立起RTP会话，需要在TEARDOWN请求中关闭RTP会话，等等...

RTSPClientSession要侦听客户端的请求，就需把自己的socket handler加入计划任务。证据如下：

[cpp]view plaincopy
 
  1. RTSPServer::RTSPClientSession::RTSPClientSession(
  2. RTSPServer&ourServer,
  3. unsignedsessionId,
  4. intclientSocket,
  5. structsockaddr_inclientAddr):
  6. fOurServer(ourServer),
  7. fOurSessionId(sessionId),
  8. fOurServerMediaSession(NULL),
  9. fClientInputSocket(clientSocket),
  10. fClientOutputSocket(clientSocket),
  11. fClientAddr(clientAddr),
  12. fSessionCookie(NULL),
  13. fLivenessCheckTask(NULL),
  14. fIsMulticast(False),
  15. fSessionIsActive(True),
  16. fStreamAfterSETUP(False),
  17. fTCPStreamIdCount(0),
  18. fNumStreamStates(0),
  19. fStreamStates(NULL),
  20. fRecursionCount(0)
  21. {
  22. //Arrangetohandleincomingrequests:
  23. resetRequestBuffer();
  24. envir().taskScheduler().turnOnBackgroundReadHandling(fClientInputSocket,
  25. (TaskScheduler::BackgroundHandlerProc*)&incomingRequestHandler,
  26. this);
  27. noteLiveness();
  28. }



下面重点讲一下下RTSPClientSession响应DESCRIBE请求的过程：

[cpp]view plaincopy
 
  1. voidRTSPServer::RTSPClientSession::handleCmd_DESCRIBE(
  2. charconst*cseq,
  3. charconst*urlPreSuffix,
  4. charconst*urlSuffix,
  5. charconst*fullRequestStr)
  6. {
  7. char*sdpDescription=NULL;
  8. char*rtspURL=NULL;
  9. do{
  10. //整理一下下RTSP地址
  11. charurlTotalSuffix[RTSP_PARAM_STRING_MAX];
  12. if(strlen(urlPreSuffix)+strlen(urlSuffix)+2
  13. >sizeofurlTotalSuffix){
  14. handleCmd_bad(cseq);
  15. break;
  16. }
  17. urlTotalSuffix[0]='\0';
  18. if(urlPreSuffix[0]!='\0'){
  19. strcat(urlTotalSuffix,urlPreSuffix);
  20. strcat(urlTotalSuffix,"/");
  21. }
  22. strcat(urlTotalSuffix,urlSuffix);
  25. //验证帐户和密码
  26. if(!authenticationOK("DESCRIBE",cseq,urlTotalSuffix,fullRequestStr))
  27. break;
  30. //Weshouldreallycheckthattherequestcontainsan"Accept:"#####
  31. //for"application/sdp",becausethat'swhatwe'resendingback#####
  34. //Beginbylookingupthe"ServerMediaSession"objectforthespecified"urlTotalSuffix":
  35. //跟据流的名字查找ServerMediaSession，如果找不到，会创建一个。每个ServerMediaSession中至少要包含一个
  36. //ServerMediaSubsession。一个ServerMediaSession对应一个媒体，可以认为是Server上的一个文件，或一个实时获取设备。其包含的每个ServerMediaSubSession代表媒体中的一个Track。所以一个ServerMediaSession对应一个媒体，如果客户请求的媒体名相同，就使用已存在的ServerMediaSession，如果不同，就创建一个新的。一个流对应一个StreamState，StreamState与ServerMediaSubsession相关，但代表的是动态的，而ServerMediaSubsession代表静态的。
  37. ServerMediaSession*session=fOurServer.lookupServerMediaSession(urlTotalSuffix);
  38. if(session==NULL){
  39. handleCmd_notFound(cseq);
  40. break;
  41. }
  44. //Then,assembleaSDPdescriptionforthissession:
  45. //获取SDP字符串，在函数内会依次获取每个ServerMediaSubSession的字符串然连接起来。
  46. sdpDescription=session->generateSDPDescription();
  47. if(sdpDescription==NULL){
  48. //Thisusuallymeansthatafilenamethatwasspecifiedfora
  49. //"ServerMediaSubsession"doesnotexist.
  50. snprintf((char*)fResponseBuffer,sizeoffResponseBuffer,
  51. "RTSP/1.0404FileNotFound,OrInIncorrectFormat\r\n"
  52. "CSeq:%s\r\n"
  53. "%s\r\n",cseq,dateHeader());
  54. break;
  55. }
  56. unsignedsdpDescriptionSize=strlen(sdpDescription);
  59. //Also,generateourRTSPURL,forthe"Content-Base:"header
  60. //(whichisnecessarytoensurethatthecorrectURLgetsusedin
  61. //subsequent"SETUP"requests).
  62. rtspURL=fOurServer.rtspURL(session,fClientInputSocket);
  65. //形成响应DESCRIBE请求的RTSP字符串。
  66. snprintf((char*)fResponseBuffer,sizeoffResponseBuffer,
  67. "RTSP/1.0200OK\r\nCSeq:%s\r\n"
  68. "%s"
  69. "Content-Base:%s/\r\n"
  70. "Content-Type:application/sdp\r\n"
  71. "Content-Length:%d\r\n\r\n"
  72. "%s",cseq,dateHeader(),rtspURL,sdpDescriptionSize,
  73. sdpDescription);
  74. }while(0);
  77. delete[]sdpDescription;
  78. delete[]rtspURL;
  81. //返回后会被立即发送（没有把socketwrite操作放入计划任务中）。
  82. }




fOurServer.lookupServerMediaSession(urlTotalSuffix)中会在找不到同名ServerMediaSession时新建一个，代表一个RTP流的ServerMediaSession们是被RTSPServer管理的，而不是被RTSPClientSession拥有。为什么呢？因为ServerMediaSession代表的是一个静态的流，也就是可以从它里面获取一个流的各种信息，但不能获取传输状态。不同客户可能连接到同一个流，所以ServerMediaSession应被RTSPServer所拥有。创建一个ServerMediaSession过程值得一观：

[cpp]view plaincopy
 
  1. staticServerMediaSession*createNewSMS(UsageEnvironment&env,charconst*fileName,FILE*/*fid*/)
  2. {
  3. //Usethefilenameextensiontodeterminethetypeof"ServerMediaSession":
  4. charconst*extension=strrchr(fileName,'.');
  5. if(extension==NULL)
  6. returnNULL;
  9. ServerMediaSession*sms=NULL;
  10. BooleanconstreuseSource=False;
  11. if(strcmp(extension,".aac")==0){
  12. //AssumedtobeanAACAudio(ADTSformat)file:
  13. NEW_SMS("AACAudio");
  14. sms->addSubsession(
  15. ADTSAudioFileServerMediaSubsession::createNew(env,fileName,
  16. reuseSource));
  17. }elseif(strcmp(extension,".amr")==0){
  18. //AssumedtobeanAMRAudiofile:
  19. NEW_SMS("AMRAudio");
  20. sms->addSubsession(
  21. AMRAudioFileServerMediaSubsession::createNew(env,fileName,
  22. reuseSource));
  23. }elseif(strcmp(extension,".ac3")==0){
  24. //AssumedtobeanAC-3Audiofile:
  25. NEW_SMS("AC-3Audio");
  26. sms->addSubsession(
  27. AC3AudioFileServerMediaSubsession::createNew(env,fileName,
  28. reuseSource));
  29. }elseif(strcmp(extension,".m4e")==0){
  30. //AssumedtobeaMPEG-4VideoElementaryStreamfile:
  31. NEW_SMS("MPEG-4Video");
  32. sms->addSubsession(
  33. MPEG4VideoFileServerMediaSubsession::createNew(env,fileName,
  34. reuseSource));
  35. }elseif(strcmp(extension,".264")==0){
  36. //AssumedtobeaH.264VideoElementaryStreamfile:
  37. NEW_SMS("H.264Video");
  38. OutPacketBuffer::maxSize=100000;//allowforsomepossiblylargeH.264frames
  39. sms->addSubsession(
  40. H264VideoFileServerMediaSubsession::createNew(env,fileName,
  41. reuseSource));
  42. }elseif(strcmp(extension,".mp3")==0){
  43. //AssumedtobeaMPEG-1or2Audiofile:
  44. NEW_SMS("MPEG-1or2Audio");
  45. //Tostreamusing'ADUs'ratherthanrawMP3frames,uncommentthefollowing:
  46. //#defineSTREAM_USING_ADUS1
  47. //ToalsoreorderADUsbeforestreaming,uncommentthefollowing:
  48. //#defineINTERLEAVE_ADUS1
  49. //(FormoreinformationaboutADUsandinterleaving,
  50. //see<http://www.live555.com/rtp-mp3/>)
  51. BooleanuseADUs=False;
  52. Interleaving*interleaving=NULL;
  53. #ifdefSTREAM_USING_ADUS
  54. useADUs=True;
  55. #ifdefINTERLEAVE_ADUS
  56. unsignedcharinterleaveCycle[]={0,2,1,3};//orchooseyourown...
  57. unsignedconstinterleaveCycleSize
  58. =(sizeofinterleaveCycle)/(sizeof(unsignedchar));
  59. interleaving=newInterleaving(interleaveCycleSize,interleaveCycle);
  60. #endif
  61. #endif
  62. sms->addSubsession(
  63. MP3AudioFileServerMediaSubsession::createNew(env,fileName,
  64. reuseSource,useADUs,interleaving));
  65. }elseif(strcmp(extension,".mpg")==0){
  66. //AssumedtobeaMPEG-1or2ProgramStream(audio+video)file:
  67. NEW_SMS("MPEG-1or2ProgramStream");
  68. MPEG1or2FileServerDemux*demux=MPEG1or2FileServerDemux::createNew(env,
  69. fileName,reuseSource);
  70. sms->addSubsession(demux->newVideoServerMediaSubsession());
  71. sms->addSubsession(demux->newAudioServerMediaSubsession());
  72. }elseif(strcmp(extension,".ts")==0){
  73. //AssumedtobeaMPEGTransportStreamfile:
  74. //Useanindexfilenamethat'sthesameastheTSfilename,exceptwith".tsx":
  75. unsignedindexFileNameLen=strlen(fileName)+2;//allowfortrailing"x\0"
  76. char*indexFileName=newchar[indexFileNameLen];
  77. sprintf(indexFileName,"%sx",fileName);
  78. NEW_SMS("MPEGTransportStream");
  79. sms->addSubsession(
  80. MPEG2TransportFileServerMediaSubsession::createNew(env,
  81. fileName,indexFileName,reuseSource));
  82. delete[]indexFileName;
  83. }elseif(strcmp(extension,".wav")==0){
  84. //AssumedtobeaWAVAudiofile:
  85. NEW_SMS("WAVAudioStream");
  86. //Toconvert16-bitPCMdatato8-bitu-law,priortostreaming,
  87. //changethefollowingtoTrue:
  88. BooleanconvertToULaw=False;
  89. sms->addSubsession(
  90. WAVAudioFileServerMediaSubsession::createNew(env,fileName,
  91. reuseSource,convertToULaw));
  92. }elseif(strcmp(extension,".dv")==0){
  93. //AssumedtobeaDVVideofile
  94. //First,makesurethattheRTPSinks'bufferswillbelargeenoughtohandlethehugesizeofDVframes(asbigas288000).
  95. OutPacketBuffer::maxSize=300000;
  98. NEW_SMS("DVVideo");
  99. sms->addSubsession(
  100. DVVideoFileServerMediaSubsession::createNew(env,fileName,
  101. reuseSource));
  102. }elseif(strcmp(extension,".mkv")==0){
  103. //AssumedtobeaMatroskafile
  104. NEW_SMS("Matroskavideo+audio+(optional)subtitles");
  107. //CreateaMatroskafileserverdemultiplexorforthespecifiedfile.(Weentertheeventlooptowaitforthistocomplete.)
  108. newMatroskaDemuxWatchVariable=0;
  109. MatroskaFileServerDemux::createNew(env,fileName,
  110. onMatroskaDemuxCreation,NULL);
  111. env.taskScheduler().doEventLoop(&newMatroskaDemuxWatchVariable);
  114. ServerMediaSubsession*smss;
  115. while((smss=demux->newServerMediaSubsession())!=NULL){
  116. sms->addSubsession(smss);
  117. }
  118. }
  121. returnsms;
  122. }

 

可以看到NEW_SMS("AMR Audio")会创建新的ServerMediaSession，之后马上调用sms->addSubsession（）为这个ServerMediaSession添加一个 ServerMediaSubSession 。看起来ServerMediaSession应该可以添加多个ServerMediaSubSession，但这里并没有这样做。如果可以添加多个 ServerMediaSubsession 那么ServerMediaSession与流名字所指定与文件是没有关系的，也就是说它不会操作文件，而文件的操作是放在 ServerMediaSubsession中的。具体应改是在ServerMediaSubsession的sdpLines()函数中打开。

 

原文地址：http://blog.csdn.net/niu_gao/article/details/6911130

live555源代码（VC6）：http://download.csdn.net/detail/leixiaohua1020/6374387

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