mp3internals.cpp

完整的RTP RTSP代码库

    }
  }
}

MP3FrameParams::~MP3FrameParams() {
}

void MP3FrameParams::setParamsFromHeader() {
  if (hdr & (1<<20)) {
    isMPEG2 = (hdr & (1<<19)) ? 0x0 : 0x1;
    isMPEG2_5 = 0;
  }
  else {
    isMPEG2 = 1;
    isMPEG2_5 = 1;
  }
  
  layer = 4-((hdr>>17)&3);
  if (layer == 4) layer = 3; // layer==4 is not allowed
  bitrateIndex = ((hdr>>12)&0xf);
  
  if (isMPEG2_5) {
    samplingFreqIndex = 6;
  } else {
    samplingFreqIndex = ((hdr>>10)&0x3) + (isMPEG2*3);
  }
  
  hasCRC = ((hdr>>16)&0x1)^0x1;
  
  padding   = ((hdr>>9)&0x1);
  extension = ((hdr>>8)&0x1);
  mode      = ((hdr>>6)&0x3);
  mode_ext  = ((hdr>>4)&0x3);
  copyright = ((hdr>>3)&0x1);
  original  = ((hdr>>2)&0x1);
  emphasis  = hdr & 0x3;
  
  stereo    = (mode == MPG_MD_MONO) ? 1 : 2;
  
  if (((hdr>>10)&0x3) == 0x3) {
#ifdef DEBUG_ERRORS
    fprintf(stderr,"Stream error - hdr: 0x%08x\n", hdr);
#endif
  }

  bitrate = tabsel_123[isMPEG2][layer-1][bitrateIndex];
  samplingFreq = freqs[samplingFreqIndex];
  isStereo = (stereo > 1);
  isFreeFormat = (bitrateIndex == 0);
  frameSize
    = ComputeFrameSize(bitrate, samplingFreq, padding, isMPEG2, layer);
  sideInfoSize = computeSideInfoSize();
 }

unsigned MP3FrameParams::computeSideInfoSize() {
  unsigned size;
  
  if (isMPEG2) {
    size = isStereo ? 17 : 9;
  } else {
    size = isStereo ? 32 : 17;
  }

  if (hasCRC) {
    size += 2;
  }

  return size;
}

unsigned ComputeFrameSize(unsigned bitrate, unsigned samplingFreq,
			  Boolean usePadding, Boolean isMPEG2,
			  unsigned char layer) {
  unsigned const bitrateMultiplier = (layer == 1) ? 12000*4 : 144000;
  unsigned framesize;

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

  return framesize;
}
#if 0
#define TRUNC_FAIRLY
static unsigned updateSideInfoSizes(MP3SideInfo& sideInfo, Boolean isMPEG2,
				    unsigned char const* mainDataPtr,
				    unsigned allowedNumBits,
				    unsigned& part23Length0a,
				    unsigned& part23Length0aTruncation,
				    unsigned& part23Length0b,
				    unsigned& part23Length0bTruncation,
				    unsigned& part23Length1a,
				    unsigned& part23Length1aTruncation,
				    unsigned& part23Length1b,
				    unsigned& part23Length1bTruncation) {
  unsigned p23L0, p23L1 = 0, p23L0Trunc = 0, p23L1Trunc = 0;

  p23L0 = sideInfo.ch[0].gr[0].part2_3_length;
  p23L1 = isMPEG2 ? 0 : sideInfo.ch[0].gr[1].part2_3_length;
#ifdef TRUNC_ONLY0
  if (p23L0 < allowedNumBits)
    allowedNumBits = p23L0;
#endif
#ifdef TRUNC_ONLY1
  if (p23L1 < allowedNumBits)
    allowedNumBits = p23L1;
#endif
  if (p23L0 + p23L1 > allowedNumBits) {
    /* We need to shorten one or both fields */
    unsigned truncation = p23L0 + p23L1 - allowedNumBits;
#ifdef TRUNC_FAIRLY
    p23L0Trunc = (truncation*p23L0)/(p23L0 + p23L1);
    p23L1Trunc = truncation - p23L0Trunc;
#endif
#if defined(TRUNC_FAVOR0) || defined(TRUNC_ONLY0)
    p23L1Trunc = (truncation>p23L1) ? p23L1 : truncation;
    p23L0Trunc = truncation - p23L1Trunc;
#endif
#if defined(TRUNC_FAVOR1) || defined(TRUNC_ONLY1)
    p23L0Trunc = (truncation>p23L0) ? p23L0 : truncation;
    p23L1Trunc = truncation - p23L0Trunc;
#endif
  }

  /* ASSERT: (p23L0Trunc <= p23L0) && (p23l1Trunc <= p23L1) */
  p23L0 -= p23L0Trunc; p23L1 -= p23L1Trunc;
#ifdef DEBUG
  fprintf(stderr, "updateSideInfoSizes (allowed: %d): %d->%d, %d->%d\n", allowedNumBits, p23L0+p23L0Trunc, p23L0, p23L1+p23L1Trunc, p23L1);
#endif

  // The truncations computed above are still estimates.  We need to 
  // adjust them so that the new fields will continue to end on
  // Huffman-encoded sample boundaries:
  updateSideInfoForHuffman(sideInfo, isMPEG2, mainDataPtr,
			   p23L0, p23L1,
			   part23Length0a, part23Length0aTruncation,
			   part23Length0b, part23Length0bTruncation,
			   part23Length1a, part23Length1aTruncation,
			   part23Length1b, part23Length1bTruncation);
  p23L0 = part23Length0a + part23Length0b;
  p23L1 = part23Length1a + part23Length1b;

  sideInfo.ch[0].gr[0].part2_3_length = p23L0;
  sideInfo.ch[0].gr[1].part2_3_length = p23L1;
  part23Length0bTruncation
    += sideInfo.ch[1].gr[0].part2_3_length; /* allow for stereo */
  sideInfo.ch[1].gr[0].part2_3_length = 0; /* output mono */
  sideInfo.ch[1].gr[1].part2_3_length = 0; /* output mono */

  return p23L0 + p23L1;
}

#endif

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

  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;
}


static void getSideInfo1(MP3FrameParams& fr, MP3SideInfo& si,
			 int stereo, int ms_stereo, long sfreq, int single) {
   int ch, gr;
   int powdiff = (single == 3) ? 4 : 0;

   /* initialize all four "part2_3_length" fields to zero: */
   si.ch[0].gr[0].part2_3_length = 0; si.ch[1].gr[0].part2_3_length = 0;
   si.ch[0].gr[1].part2_3_length = 0; si.ch[1].gr[1].part2_3_length = 0;

   si.main_data_begin = fr.getBits(9);
   if (stereo == 1)
     si.private_bits = fr.getBits(5);
   else 
     si.private_bits = fr.getBits(3);

   for (ch=0; ch<stereo; ch++) {
       si.ch[ch].gr[0].scfsi = -1;
       si.ch[ch].gr[1].scfsi = fr.getBits(4);
   }

   for (gr=0; gr<2; gr++) {
     for (ch=0; ch<stereo; ch++) {
       MP3SideInfo::gr_info_s_t& gr_info = si.ch[ch].gr[gr];

       gr_info.part2_3_length = fr.getBits(12);
       gr_info.big_values = fr.getBits(9);
       gr_info.global_gain = fr.getBits(8);
       gr_info.pow2gain = gainpow2+256 - gr_info.global_gain + powdiff;
       if (ms_stereo) gr_info.pow2gain += 2;
       gr_info.scalefac_compress = fr.getBits(4);
/* window-switching flag == 1 for block_Type != 0 .. and block-type == 0 -> win-sw-flag = 0 */
       gr_info.window_switching_flag = fr.get1Bit();
       if (gr_info.window_switching_flag) {
         int i;
         gr_info.block_type = fr.getBits(2);
         gr_info.mixed_block_flag = fr.get1Bit();
         gr_info.table_select[0] = fr.getBits(5);
         gr_info.table_select[1] = fr.getBits(5);
         /*
          * table_select[2] not needed, because there is no region2,
          * but to satisfy some verifications tools we set it either.
          */
         gr_info.table_select[2] = 0;
         for (i=0;i<3;i++) {
	   gr_info.subblock_gain[i] = fr.getBits(3);
           gr_info.full_gain[i]
	     = gr_info.pow2gain + ((gr_info.subblock_gain[i])<<3);
	 }

#ifdef DEBUG_ERRORS
         if (gr_info.block_type == 0) {
           fprintf(stderr,"Blocktype == 0 and window-switching == 1 not allowed.\n");
         }
#endif
         /* region_count/start parameters are implicit in this case. */       
         gr_info.region1start = 36>>1;
         gr_info.region2start = 576>>1;
       }
       else 
       {
         int i,r0c,r1c;
         for (i=0; i<3; i++) {
	   gr_info.table_select[i] = fr.getBits(5);
	 }
         r0c = gr_info.region0_count = fr.getBits(4);
         r1c = gr_info.region1_count = fr.getBits(3);
         gr_info.region1start = bandInfo[sfreq].longIdx[r0c+1] >> 1 ;
         gr_info.region2start = bandInfo[sfreq].longIdx[r0c+1+r1c+1] >> 1;
         gr_info.block_type = 0;
         gr_info.mixed_block_flag = 0;
       }
       gr_info.preflag = fr.get1Bit();
       gr_info.scalefac_scale = fr.get1Bit();
       gr_info.count1table_select = fr.get1Bit();
     }
   }
}

static void getSideInfo2(MP3FrameParams& fr, MP3SideInfo& si,
			 int stereo, int ms_stereo, long sfreq, int single) {
   int ch;
   int powdiff = (single == 3) ? 4 : 0;

   /* initialize all four "part2_3_length" fields to zero: */
   si.ch[0].gr[0].part2_3_length = 0; si.ch[1].gr[0].part2_3_length = 0;
   si.ch[0].gr[1].part2_3_length = 0; si.ch[1].gr[1].part2_3_length = 0;

   si.main_data_begin = fr.getBits(8);
   if (stereo == 1)
     si.private_bits = fr.get1Bit();
   else 
     si.private_bits = fr.getBits(2);

   for (ch=0; ch<stereo; ch++) {
       MP3SideInfo::gr_info_s_t& gr_info = si.ch[ch].gr[0];

       gr_info.part2_3_length = fr.getBits(12);
       si.ch[ch].gr[1].part2_3_length = 0; /* to ensure granule 1 unused */

       gr_info.big_values = fr.getBits(9);
       gr_info.global_gain = fr.getBits(8);
       gr_info.pow2gain = gainpow2+256 - gr_info.global_gain + powdiff;
       if (ms_stereo) gr_info.pow2gain += 2;
       gr_info.scalefac_compress = fr.getBits(9);
/* window-switching flag == 1 for block_Type != 0 .. and block-type == 0 -> win-sw-flag = 0 */
       gr_info.window_switching_flag = fr.get1Bit();
       if (gr_info.window_switching_flag) {
         int i;
         gr_info.block_type = fr.getBits(2);
         gr_info.mixed_block_flag = fr.get1Bit();
         gr_info.table_select[0] = fr.getBits(5);
         gr_info.table_select[1] = fr.getBits(5);
         /*
          * table_select[2] not needed, because there is no region2,
          * but to satisfy some verifications tools we set it either.
          */
         gr_info.table_select[2] = 0;
         for (i=0;i<3;i++) {
	   gr_info.subblock_gain[i] = fr.getBits(3);
           gr_info.full_gain[i]
	     = gr_info.pow2gain + ((gr_info.subblock_gain[i])<<3);
	 }

#ifdef DEBUG_ERRORS
         if (gr_info.block_type == 0) {
           fprintf(stderr,"Blocktype == 0 and window-switching == 1 not allowed.\n");
         }
#endif
         /* region_count/start parameters are implicit in this case. */       
/* check this again! */
         if (gr_info.block_type == 2)
           gr_info.region1start = 36>>1;
         else {
           gr_info.region1start = 54>>1;
         }