mp3adu.cpp

流媒体传输协议的实现代码,非常有用.可以支持rtsp mms等流媒体传输协议

	packetIsLost = (our_random()%10 == 0); // simulate 10% packet loss #####
      }

      if (packetIsLost) {
	// Read and discard the next input frame (that would be part of
	// a lost packet):
	Segment dummySegment;
	unsigned numBytesRead;
	struct timeval presentationTime;
	// (this works only if the source can be read synchronously)
	fInputSource->syncGetNextFrame(dummySegment.buf,
				       sizeof dummySegment.buf, numBytesRead,
				       presentationTime);
      } else {
	break; // from while (1)
      }
    }
#endif

    fAreEnqueueingADU = True;
    fSegments->enqueueNewSegment(fInputSource, this);
  } else {
    // Return a frame now:
    generateFrameFromHeadADU();
        // sets fFrameSize, fPresentationTime, and fDurationInMicroseconds

    // Call our own 'after getting' function.  Because we're not a 'leaf'
    // source, we can call this directly, without risking infinite recursion.
    afterGetting(this);
  }
}

Boolean MP3FromADUSource::needToGetAnADU() {
  // Check whether we need to first enqueue a new ADU before we
  // can generate a frame for our head ADU.
  Boolean needToEnqueue = True;

  if (!fSegments->isEmpty()) {
    unsigned index = fSegments->headIndex();
    Segment* seg = &(fSegments->headSegment());
    int const endOfHeadFrame = (int) seg->dataHere();
    unsigned frameOffset = 0;
    
    while (1) {
      int endOfData = frameOffset - seg->backpointer + seg->aduSize;
      if (endOfData >= endOfHeadFrame) {
	// We already have enough data to generate a frame
	needToEnqueue = False;
	break;
      }
      
      frameOffset += seg->dataHere();
      index = SegmentQueue::nextIndex(index);
      if (index == fSegments->nextFreeIndex()) break;
      seg = &(fSegments->s[index]);
    }
  }
  
  return needToEnqueue;
}

void MP3FromADUSource::insertDummyADUsIfNecessary() {
  if (fSegments->isEmpty()) return; // shouldn't happen

  // The tail segment (ADU) is assumed to have been recently
  // enqueued.  If its backpointer would overlap the data
  // of the previous ADU, then we need to insert one or more
  // empty, 'dummy' ADUs ahead of it.  (This situation should occur
  // only if an intermediate ADU was lost.)
  
  unsigned tailIndex
    = SegmentQueue::prevIndex(fSegments->nextFreeIndex());
  Segment* tailSeg = &(fSegments->s[tailIndex]);
  
  while (1) {
    unsigned prevADUend; // relative to the start of the new ADU
    if (fSegments->headIndex() != tailIndex) {
      // there is a previous segment
      unsigned prevIndex = SegmentQueue::prevIndex(tailIndex);
      Segment& prevSegment = fSegments->s[prevIndex];
      prevADUend = prevSegment.dataHere() + prevSegment.backpointer;
      if (prevSegment.aduSize > prevADUend) {
	// shouldn't happen if the previous ADU was well-formed
	prevADUend = 0;
      } else {
	prevADUend -= prevSegment.aduSize;
      }
    } else {
      prevADUend = 0;
    }
    
    if (tailSeg->backpointer > prevADUend) {
      // We need to insert a dummy ADU in front of the tail
#ifdef DEBUG
      fprintf(stderr, "a->m:need to insert a dummy ADU (%d, %d, %d) [%d, %d]\n", tailSeg->backpointer, prevADUend, tailSeg->dataHere(), fSegments->headIndex(), fSegments->nextFreeIndex());
#endif
      tailIndex = fSegments->nextFreeIndex();
      if (!fSegments->insertDummyBeforeTail(prevADUend)) return;
      tailSeg = &(fSegments->s[tailIndex]);
    } else {
      break; // no more dummy ADUs need to be inserted
    }
  }
}

Boolean MP3FromADUSource::generateFrameFromHeadADU() {
    // Output a frame for the head ADU:
    if (fSegments->isEmpty()) return False;
    unsigned index = fSegments->headIndex();
    Segment* seg = &(fSegments->headSegment());
#ifdef DEBUG
    fprintf(stderr, "a->m:outputting frame for %d<-%d (fs %d, dh %d), (descriptorSize: %d)\n", seg->aduSize, seg->backpointer, seg->frameSize, seg->dataHere(), seg->descriptorSize);
#endif
    unsigned char* toPtr = fTo;
    
    // output header and side info:
    fFrameSize = seg->frameSize;
    fPresentationTime = seg->presentationTime;
    fDurationInMicroseconds = seg->durationInMicroseconds;
    memmove(toPtr, seg->dataStart(), seg->headerSize + seg->sideInfoSize);
    toPtr += seg->headerSize + seg->sideInfoSize;
    
    // zero out the rest of the frame, in case ADU data doesn't fill it all in
    unsigned bytesToZero = seg->dataHere(); 
    for (unsigned i = 0; i < bytesToZero; ++i) {
      toPtr[i] = '\0';
    }
    
    // Fill in the frame with appropriate ADU data from this and
    // subsequent ADUs:
    unsigned frameOffset = 0;
    unsigned toOffset = 0;
    unsigned const endOfHeadFrame = seg->dataHere();

    while (toOffset < endOfHeadFrame) {
      int startOfData = frameOffset - seg->backpointer;
      if (startOfData > (int)endOfHeadFrame) break; // no more ADUs needed
      
      int endOfData = startOfData + seg->aduSize;
      if (endOfData > (int)endOfHeadFrame) {
	endOfData = endOfHeadFrame;
      }
      
      unsigned fromOffset;
      if (startOfData <= (int)toOffset) {
	fromOffset = toOffset - startOfData;
	startOfData = toOffset;
	if (endOfData < startOfData) endOfData = startOfData;
      } else {
	fromOffset = 0;
	
	// we may need some padding bytes beforehand
	unsigned bytesToZero = startOfData - toOffset;
#ifdef DEBUG
	if (bytesToZero > 0) fprintf(stderr, "a->m:outputting %d zero bytes (%d, %d, %d, %d)\n", bytesToZero, startOfData, toOffset, frameOffset, seg->backpointer);
#endif
	toOffset += bytesToZero;
      }
      
      unsigned char* fromPtr
	= &seg->dataStart()[seg->headerSize + seg->sideInfoSize + fromOffset];
      unsigned bytesUsedHere = endOfData - startOfData;
#ifdef DEBUG
      if (bytesUsedHere > 0) fprintf(stderr, "a->m:outputting %d bytes from %d<-%d\n", bytesUsedHere, seg->aduSize, seg->backpointer);
#endif
      memmove(toPtr + toOffset, fromPtr, bytesUsedHere);
      toOffset += bytesUsedHere;
      
      frameOffset += seg->dataHere();
      index = SegmentQueue::nextIndex(index);
      if (index == fSegments->nextFreeIndex()) break;
      seg = &(fSegments->s[index]);
    }
    
    fSegments->dequeue();

    return True;
}


////////// Segment //////////

unsigned Segment::dataHere() {
  int result = frameSize - (headerSize + sideInfoSize);
  if (result < 0) {
    return 0;
  }

  return (unsigned)result;
} 

////////// SegmentQueue //////////

void SegmentQueue::enqueueNewSegment(FramedSource* inputSource,
				     FramedSource* usingSource) {
  if (isFull()) {
    usingSource->envir() << "SegmentQueue::enqueueNewSegment() overflow\n";
    FramedSource::handleClosure(usingSource);
    return;
  }
  
  fUsingSource = usingSource;
  
  Segment& seg = nextFreeSegment();
  inputSource->getNextFrame(seg.buf, sizeof seg.buf,
			    sqAfterGettingSegment, this,
			    FramedSource::handleClosure, usingSource);
}

void SegmentQueue::sqAfterGettingSegment(void* clientData,
					 unsigned numBytesRead,
					 unsigned /*numTruncatedBytes*/,
					 struct timeval presentationTime,
					 unsigned durationInMicroseconds) {
  SegmentQueue* segQueue = (SegmentQueue*)clientData;
  Segment& seg = segQueue->nextFreeSegment();

  seg.presentationTime = presentationTime;
  seg.durationInMicroseconds = durationInMicroseconds;

  if (segQueue->sqAfterGettingCommon(seg, numBytesRead)) {
#ifdef DEBUG
    char const* direction = segQueue->fDirectionIsToADU ? "m->a" : "a->m";
    fprintf(stderr, "%s:read frame %d<-%d, fs:%d, sis:%d, dh:%d, (descriptor size: %d)\n", direction, seg.aduSize, seg.backpointer, seg.frameSize, seg.sideInfoSize, seg.dataHere(), seg.descriptorSize);
#endif
  }

  // Continue our original calling source where it left off:
  segQueue->fUsingSource->doGetNextFrame();
}

// Common code called after a new segment is enqueued
Boolean SegmentQueue::sqAfterGettingCommon(Segment& seg,
					   unsigned numBytesRead) { 
  unsigned char* fromPtr = seg.buf;

  if (fIncludeADUdescriptors) {
    // The newly-read data is assumed to be an ADU with a descriptor
    // in front
    (void)ADUdescriptor::getRemainingFrameSize(fromPtr);
    seg.descriptorSize = (unsigned)(fromPtr-seg.buf);
  } else {
    seg.descriptorSize = 0;
  }

  // parse the MP3-specific info in the frame to get the ADU params
  unsigned hdr;
  MP3SideInfo sideInfo;
  if (!GetADUInfoFromMP3Frame(fromPtr, numBytesRead,
			      hdr, seg.frameSize,
			      sideInfo, seg.sideInfoSize,
			      seg.backpointer, seg.aduSize)) {
    return False;
  }
  
  // If we've just read an ADU (rather than a regular MP3 frame), then use the
  // entire "numBytesRead" data for the 'aduSize', so that we include any
  // 'ancillary data' that may be present at the end of the ADU:
  if (!fDirectionIsToADU) {
    unsigned newADUSize
      = numBytesRead - seg.descriptorSize - 4/*header size*/ - seg.sideInfoSize;
    if (newADUSize > seg.aduSize) seg.aduSize = newADUSize;
  }
  fTotalDataSize += seg.dataHere();
  fNextFreeIndex = nextIndex(fNextFreeIndex);

  return True;
}

Boolean SegmentQueue::dequeue() {
  if (isEmpty()) {
    fUsingSource->envir() << "SegmentQueue::dequeue(): underflow!\n";
    return False;
  }

  Segment& seg = s[headIndex()];
  fTotalDataSize -= seg.dataHere();
  fHeadIndex = nextIndex(fHeadIndex);
  return True;
}

Boolean SegmentQueue::insertDummyBeforeTail(unsigned backpointer) {
  if (isEmptyOrFull()) return False;

  // Copy the current tail segment to its new position, then modify the
  // old tail segment to be a 'dummy' ADU

  unsigned newTailIndex = nextFreeIndex();
  Segment& newTailSeg = s[newTailIndex];

  unsigned oldTailIndex = prevIndex(newTailIndex);
  Segment& oldTailSeg = s[oldTailIndex];

  newTailSeg = oldTailSeg; // structure copy

  // Begin by setting (replacing) the ADU descriptor of the dummy ADU:
  unsigned char* ptr = oldTailSeg.buf;
  if (fIncludeADUdescriptors) {
    unsigned remainingFrameSize
      = oldTailSeg.headerSize + oldTailSeg.sideInfoSize + 0 /* 0-size ADU */;
    unsigned currentDescriptorSize = oldTailSeg.descriptorSize;

    if (currentDescriptorSize == 2) {
      ADUdescriptor::generateTwoByteDescriptor(ptr, remainingFrameSize);
    } else {
      (void)ADUdescriptor::generateDescriptor(ptr, remainingFrameSize);
    }
  }

  // Then zero out the side info of the dummy frame:
  if (!ZeroOutMP3SideInfo(ptr, oldTailSeg.frameSize,
			  backpointer)) return False;

  unsigned dummyNumBytesRead
    = oldTailSeg.descriptorSize + 4/*header size*/ + oldTailSeg.sideInfoSize;
  return sqAfterGettingCommon(oldTailSeg, dummyNumBytesRead);
}