mp3adudescriptor.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

/**********
This library is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the
Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version. (See <http://www.gnu.org/copyleft/lesser.html>.)

This library is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
more details.

You should have received a copy of the GNU Lesser General Public License
along with this library; if not, write to the Free Software Foundation, Inc.,
59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
**********/
// "liveMedia"
// Copyright (c) 1996-2004 Live Networks, Inc.  All rights reserved.
// Descriptor preceding frames of 'ADU' MP3 streams (for improved loss-tolerance)
// Implementation

#include "MP3ADUdescriptor.hh"

////////// ADUdescriptor //////////

//##### NOTE: For now, ignore fragmentation.  Fix this later! #####

#define TWO_BYTE_DESCR_FLAG 0x40

unsigned ADUdescriptor::generateDescriptor(unsigned char*& toPtr,
					   unsigned remainingFrameSize) {
  unsigned descriptorSize = ADUdescriptor::computeSize(remainingFrameSize);
  switch (descriptorSize) {
  case 1: {
    *toPtr++ = (unsigned char)remainingFrameSize;
    break;
  }
  case 2: {
    generateTwoByteDescriptor(toPtr, remainingFrameSize);
    break;
  }
  }

  return descriptorSize;
}

void ADUdescriptor::generateTwoByteDescriptor(unsigned char*& toPtr,
					      unsigned remainingFrameSize) {
  *toPtr++ = (TWO_BYTE_DESCR_FLAG|(unsigned char)(remainingFrameSize>>8));
  *toPtr++ = (unsigned char)(remainingFrameSize&0xFF);
}

unsigned ADUdescriptor::getRemainingFrameSize(unsigned char*& fromPtr) {
  unsigned char firstByte = *fromPtr++;

  if (firstByte&TWO_BYTE_DESCR_FLAG) {
    // This is a 2-byte descriptor
    unsigned char secondByte = *fromPtr++;

    return ((firstByte&0x3F)<<8) | secondByte;
  } else {
    // This is a 1-byte descriptor
    return (firstByte&0x3F); 
  }
}