liveMedia/MP3Internals.hh File Reference

#include "Boolean.hh"
#include "BitVector.hh"

Include dependency graph for MP3Internals.hh:

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Go to the source code of this file.

Data Structures
struct	MP3SideInfo
struct	MP3SideInfo::gr_info_s
class	MP3FrameParams
Defines
#define	SBLIMIT   32
#define	MAX_MP3_FRAME_SIZE   2500
Typedefs
typedef MP3SideInfo	MP3SideInfo_t
Functions
unsigned	ComputeFrameSize (unsigned bitrate, unsigned samplingFreq, Boolean usePadding, Boolean isMPEG2, unsigned char layer)
Boolean	GetADUInfoFromMP3Frame (unsigned char const *framePtr, unsigned totFrameSize, unsigned &hdr, unsigned &frameSize, MP3SideInfo &sideInfo, unsigned &sideInfoSize, unsigned &backpointer, unsigned &aduSize)
Boolean	ZeroOutMP3SideInfo (unsigned char *framePtr, unsigned totFrameSize, unsigned newBackpointer)
unsigned	TranscodeMP3ADU (unsigned char const *fromPtr, unsigned fromSize, unsigned toBitrate, unsigned char *toPtr, unsigned toMaxSize, unsigned &availableBytesForBackpointer)

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Define Documentation

#define MAX_MP3_FRAME_SIZE   2500

Definition at line 64 of file MP3Internals.hh.

Referenced by MP3ADUTranscoder::doGetNextFrame().

#define SBLIMIT   32

Definition at line 63 of file MP3Internals.hh.

Referenced by MP3HuffmanEncodingInfo::MP3HuffmanEncodingInfo().

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Typedef Documentation

typedef struct MP3SideInfo MP3SideInfo_t

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Function Documentation

unsigned ComputeFrameSize	(	unsigned	bitrate,
		unsigned	samplingFreq,
		Boolean	usePadding,
		Boolean	isMPEG2,
		unsigned char	layer
	)

Definition at line 219 of file MP3Internals.cpp.

Referenced by MP3FrameParams::setParamsFromHeader().

                                               {
  if (samplingFreq == 0) return 0;
  unsigned const bitrateMultiplier = (layer == 1) ? 12000*4 : 144000;
  unsigned framesize;

  framesize = bitrate*bitrateMultiplier;
  framesize /= samplingFreq<<isMPEG2;
  framesize = framesize + usePadding - 4;

  return framesize;
}

Boolean GetADUInfoFromMP3Frame	(	unsigned char const *	framePtr,
		unsigned	totFrameSize,
		unsigned &	hdr,
		unsigned &	frameSize,
		MP3SideInfo &	sideInfo,
		unsigned &	sideInfoSize,
		unsigned &	backpointer,
		unsigned &	aduSize
	)

Definition at line 303 of file MP3Internals.cpp.

References MP3SideInfo::ch, False, MP3FrameParams::frameSize, MP3FrameParams::getSideInfo(), MP3SideInfo::gr, MP3FrameParams::hdr, MP3FrameParams::layer, MP3SideInfo::main_data_begin, MP3FrameParams::setBytePointer(), MP3FrameParams::setParamsFromHeader(), MP3FrameParams::sideInfoSize, and True.

Referenced by SegmentQueue::sqAfterGettingCommon(), and TranscodeMP3ADU().

                                                                         {
  if (totFrameSize < 4) return False; // there's not enough data

  MP3FrameParams fr;
  fr.hdr =   ((unsigned)framePtr[0] << 24) | ((unsigned)framePtr[1] << 16)
           | ((unsigned)framePtr[2] << 8) | (unsigned)framePtr[3];
  fr.setParamsFromHeader();
  fr.setBytePointer(framePtr + 4, totFrameSize - 4); // skip hdr

  frameSize = 4 + fr.frameSize;

  if (fr.layer != 3) {
    // Special case for non-layer III frames
    backpointer = 0;
    sideInfoSize = 0;
    aduSize = fr.frameSize;
    return True;
  }

  sideInfoSize = fr.sideInfoSize;
  if (totFrameSize < 4 + sideInfoSize) return False; // not enough data

  fr.getSideInfo(sideInfo);

  hdr = fr.hdr;
  backpointer = sideInfo.main_data_begin;
  unsigned numBits = sideInfo.ch[0].gr[0].part2_3_length;
  numBits += sideInfo.ch[0].gr[1].part2_3_length;
  numBits += sideInfo.ch[1].gr[0].part2_3_length;
  numBits += sideInfo.ch[1].gr[1].part2_3_length;
  aduSize = (numBits+7)/8;
#ifdef DEBUG
  fprintf(stderr, "mp3GetADUInfoFromFrame: hdr: %08x, frameSize: %d, part2_3_lengths: %d,%d,%d,%d, aduSize: %d, backpointer: %d\n", hdr, frameSize, sideInfo.ch[0].gr[0].part2_3_length, sideInfo.ch[0].gr[1].part2_3_length, sideInfo.ch[1].gr[0].part2_3_length, sideInfo.ch[1].gr[1].part2_3_length, aduSize, backpointer);
#endif

  return True;
}

unsigned TranscodeMP3ADU	(	unsigned char const *	fromPtr,
		unsigned	fromSize,
		unsigned	toBitrate,
		unsigned char *	toPtr,
		unsigned	toMaxSize,
		unsigned &	availableBytesForBackpointer
	)

Definition at line 707 of file MP3Internals.cpp.

References assignADUBackpointer(), MP3FrameParams::frameSize, GetADUInfoFromMP3Frame(), MP3FrameParams::hdr, MP3FrameParams::isMPEG2, MP3BitrateToBitrateIndex(), outputHeader(), PutMP3SideInfoIntoFrame(), MP3FrameParams::setParamsFromHeader(), shiftBits(), MP3FrameParams::sideInfoSize, and updateSideInfoSizes().

Referenced by MP3ADUTranscoder::afterGettingFrame1().

                                                              {
  // Begin by parsing the input ADU's parameters:
  unsigned hdr, inFrameSize, inSideInfoSize, backpointer, inAduSize;
  MP3SideInfo sideInfo;
  if (!GetADUInfoFromMP3Frame(fromPtr, fromSize,
                              hdr, inFrameSize, sideInfo, inSideInfoSize,
                              backpointer, inAduSize)) {
    return 0;
  }
  fromPtr += (4+inSideInfoSize); // skip to 'main data'

  // Alter the 4-byte MPEG header to reflect the output ADU:
  // (different bitrate; mono; no CRC)
  Boolean isMPEG2 = ((hdr&0x00080000) == 0);
  unsigned toBitrateIndex = MP3BitrateToBitrateIndex(toBitrate, isMPEG2);
  hdr &=~ 0xF000; hdr |= (toBitrateIndex<<12); // set bitrate index
  hdr |= 0x10200; // turn on !error-prot and padding bits
  hdr &=~ 0xC0; hdr |= 0xC0; // set mode to 3 (mono)

  // Set up the rest of the parameters of the new ADU:
  MP3FrameParams outFr;
  outFr.hdr = hdr;
  outFr.setParamsFromHeader();

  // Figure out how big to make the output ADU:
  unsigned inAveAduSize = inFrameSize - inSideInfoSize;
  unsigned outAveAduSize = outFr.frameSize - outFr.sideInfoSize;
  unsigned desiredOutAduSize /*=inAduSize*outAveAduSize/inAveAduSize*/
    = (2*inAduSize*outAveAduSize + inAveAduSize)/(2*inAveAduSize);
      // this rounds to the nearest integer

  if (toMaxSize < (4 + outFr.sideInfoSize)) return 0;
  unsigned maxOutAduSize = toMaxSize - (4 + outFr.sideInfoSize);
  if (desiredOutAduSize > maxOutAduSize) {
    desiredOutAduSize = maxOutAduSize;
  }

  // Figure out the new sizes of the various 'part23 lengths',
  // and how much they are truncated:
  unsigned part23Length0a, part23Length0aTruncation;
  unsigned part23Length0b, part23Length0bTruncation;
  unsigned part23Length1a, part23Length1aTruncation;
  unsigned part23Length1b, part23Length1bTruncation;
  unsigned numAduBits
    = updateSideInfoSizes(sideInfo, outFr.isMPEG2,
                          fromPtr, 8*desiredOutAduSize,
                          part23Length0a, part23Length0aTruncation,
                          part23Length0b, part23Length0bTruncation,
                          part23Length1a, part23Length1aTruncation,
                          part23Length1b, part23Length1bTruncation);
#ifdef DEBUG
fprintf(stderr, "shrinkage %d->%d [(%d,%d),(%d,%d)] (trunc: [(%d,%d),(%d,%d)]) {%d}\n", inAduSize, (numAduBits+7)/8,
              part23Length0a, part23Length0b, part23Length1a, part23Length1b,
              part23Length0aTruncation, part23Length0bTruncation,
              part23Length1aTruncation, part23Length1bTruncation,
              maxOutAduSize);
#endif
 unsigned actualOutAduSize = (numAduBits+7)/8;

 // Give the new ADU an appropriate 'backpointer':
 assignADUBackpointer(outFr, actualOutAduSize, sideInfo, availableBytesForBackpointer);


 // 4-byte header
 outputHeader(toPtr, hdr); toPtr += 4;

 // side info
 PutMP3SideInfoIntoFrame(sideInfo, outFr, toPtr); toPtr += outFr.sideInfoSize;

 // 'main data', using the new lengths
 unsigned toBitOffset = 0;
 unsigned fromBitOffset = 0;

 /* rebuild portion 0a: */
 memmove(toPtr, fromPtr, (part23Length0a+7)/8);
 toBitOffset += part23Length0a;
 fromBitOffset += part23Length0a + part23Length0aTruncation;

 /* rebuild portion 0b: */
 shiftBits(toPtr, toBitOffset, fromPtr, fromBitOffset, part23Length0b);
 toBitOffset += part23Length0b;
 fromBitOffset += part23Length0b + part23Length0bTruncation;

 /* rebuild portion 1a: */
 shiftBits(toPtr, toBitOffset, fromPtr, fromBitOffset, part23Length1a);
 toBitOffset += part23Length1a;
 fromBitOffset += part23Length1a + part23Length1aTruncation;

 /* rebuild portion 1b: */
 shiftBits(toPtr, toBitOffset, fromPtr, fromBitOffset, part23Length1b);
 toBitOffset += part23Length1b;

 /* zero out any remaining bits (probably unnecessary, but...) */
 unsigned char const zero = '\0';
 shiftBits(toPtr, toBitOffset, &zero, 0,
           actualOutAduSize*8 - numAduBits);

 return 4 + outFr.sideInfoSize + actualOutAduSize;
}

Boolean ZeroOutMP3SideInfo	(	unsigned char *	framePtr,
		unsigned	totFrameSize,
		unsigned	newBackpointer
	)

Definition at line 636 of file MP3Internals.cpp.

References MP3SideInfo::ch, False, MP3FrameParams::getSideInfo(), MP3SideInfo::gr, MP3FrameParams::hdr, MP3SideInfo::main_data_begin, PutMP3SideInfoIntoFrame(), MP3FrameParams::setBytePointer(), MP3FrameParams::setParamsFromHeader(), MP3FrameParams::sideInfoSize, and True.

Referenced by SegmentQueue::insertDummyBeforeTail().

                                                    {
  if (totFrameSize < 4) return False; // there's not enough data

  MP3FrameParams fr;
  fr.hdr =   ((unsigned)framePtr[0] << 24) | ((unsigned)framePtr[1] << 16)
           | ((unsigned)framePtr[2] << 8) | (unsigned)framePtr[3];
  fr.setParamsFromHeader();
  fr.setBytePointer(framePtr + 4, totFrameSize - 4); // skip hdr

  if (totFrameSize < 4 + fr.sideInfoSize) return False; // not enough data

  MP3SideInfo si;
  fr.getSideInfo(si);

  si.main_data_begin = newBackpointer; /* backpointer */
  /* set all four "part2_3_length" and "big_values" fields to zero: */
  si.ch[0].gr[0].part2_3_length = si.ch[0].gr[0].big_values = 0;
  si.ch[1].gr[0].part2_3_length = si.ch[1].gr[0].big_values = 0;
  si.ch[0].gr[1].part2_3_length = si.ch[0].gr[1].big_values = 0;
  si.ch[1].gr[1].part2_3_length = si.ch[1].gr[1].big_values = 0;

  PutMP3SideInfoIntoFrame(si, fr, framePtr + 4);

  return True;
}

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