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RTP packet handler

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cpp code to parse packet headers and find the actual audio frames in the packet

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  1. void MultiFramedRTPSource::networkReadHandler1() {
  2.   BufferedPacket* bPacket = fPacketReadInProgress;
  3.   if (bPacket == NULL) {
  4.     // Normal case: Get a free BufferedPacket descriptor to hold the new network packet:
  5.     bPacket = fReorderingBuffer->getFreePacket(this);
  6.   }
  7.  
  8.   // Read the network packet, and perform sanity checks on the RTP header:
  9.   Boolean readSuccess = False;
  10.   do {
  11.     Boolean packetReadWasIncomplete = fPacketReadInProgress != NULL;
  12.     if (!bPacket->fillInData(fRTPInterface, packetReadWasIncomplete)) break;
  13.     if (packetReadWasIncomplete) {
  14.       // We need additional read(s) before we can process the incoming packet:
  15.       fPacketReadInProgress = bPacket;
  16.       return;
  17.     } else {
  18.       fPacketReadInProgress = NULL;
  19.     }
  20. #ifdef TEST_LOSS
  21.     setPacketReorderingThresholdTime(0);
  22.        // don't wait for 'lost' packets to arrive out-of-order later
  23.     if ((our_random()%10) == 0) break; // simulate 10% packet loss
  24. #endif
  25.  
  26.     // Check for the 12-byte RTP header:
  27.     if (bPacket->dataSize() < 12) break;
  28.     unsigned rtpHdr = ntohl(*(u_int32_t*)(bPacket->data())); ADVANCE(4);
  29.     Boolean rtpMarkerBit = (rtpHdr&0x00800000) >> 23;
  30.     unsigned rtpTimestamp = ntohl(*(u_int32_t*)(bPacket->data()));ADVANCE(4);
  31.     unsigned rtpSSRC = ntohl(*(u_int32_t*)(bPacket->data())); ADVANCE(4);
  32.     // rcr it looks like the java version has 10 extra bytes after SSRC
  33.     // Check the RTP version number (it should be 2):
  34.     if ((rtpHdr&0xC0000000) != 0x80000000) break;
  35.  
  36.     // Skip over any CSRC identifiers in the header:
  37.     unsigned cc = (rtpHdr>>24)&0xF;
  38.     if (bPacket->dataSize() < cc) break;
  39.     ADVANCE(cc*4);
  40.  
  41.     //rcr  the above does not seem to be skipping any bytes
  42.  
  43.     // Check for (& ignore) any RTP header extension
  44.     if (rtpHdr&0x10000000) {
  45.       if (bPacket->dataSize() < 4) break;
  46.       unsigned extHdr = ntohl(*(u_int32_t*)(bPacket->data())); ADVANCE(4);
  47.       unsigned remExtSize = 4*(extHdr&0xFFFF);
  48.       if (bPacket->dataSize() < remExtSize) break;
  49.       ADVANCE(remExtSize);
  50.     }
  51.     //rcr the above does not seem to b skipping
  52.  
  53.     // Discard any padding bytes:
  54.     if (rtpHdr&0x20000000) {
  55.       if (bPacket->dataSize() == 0) break;
  56.       unsigned numPaddingBytes
  57. 	= (unsigned)(bPacket->data())[bPacket->dataSize()-1];
  58.       if (bPacket->dataSize() < numPaddingBytes) break;
  59.       bPacket->removePadding(numPaddingBytes);
  60.     }
  61.  
  62.     //rcr the above does not seem skipping bytes
  63.  
  64.     // Check the Payload Type.
  65.     if ((unsigned char)((rtpHdr&0x007F0000)>>16)
  66. 	!= rtpPayloadFormat()) {
  67.       break;
  68.     }
  69.  
  70.     // The rest of the packet is the usable data.  Record and save it:
  71.     fLastReceivedSSRC = rtpSSRC;
  72.     unsigned short rtpSeqNo = (unsigned short)(rtpHdr&0xFFFF);
  73.     Boolean usableInJitterCalculation
  74.       = packetIsUsableInJitterCalculation((bPacket->data()),
  75. 						  bPacket->dataSize());
  76.     struct timeval presentationTime; // computed by:
  77.     Boolean hasBeenSyncedUsingRTCP; // computed by:
  78.     receptionStatsDB()
  79.       .noteIncomingPacket(rtpSSRC, rtpSeqNo, rtpTimestamp,
  80. 			  timestampFrequency(),
  81. 			  usableInJitterCalculation, presentationTime,
  82. 			  hasBeenSyncedUsingRTCP, bPacket->dataSize());
  83.     //rcr this dataSize is the same as the java getPacketData().length
  84.     // envir() << "M-frmRTPsrc.readHndlr pck sz " << bPacket->dataSize();
  85.  
  86.     // Fill in the rest of the packet descriptor, and store it:
  87.     struct timeval timeNow;
  88.     gettimeofday(&timeNow, NULL);
  89.     bPacket->assignMiscParams(rtpSeqNo, rtpTimestamp, presentationTime,
  90. 			      hasBeenSyncedUsingRTCP, rtpMarkerBit,
  91. 			      timeNow);
  92.     if (!fReorderingBuffer->storePacket(bPacket)) break;
  93.  
  94.     readSuccess = True;
  95.   } while (0);
  96.   if (!readSuccess) fReorderingBuffer->freePacket(bPacket);
  97.  
  98.   doGetNextFrame1();
  99.   // If we didn't get proper data this time, we'll get another chance
  100. }

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