www.pudn.com > mediator15src.zip > common.c

/* All modifications to the original file common.c are 
 * Copyright (C) 2001 Arno Hornberger  
 */ 
 
#include "mpg123.h" 
 
static const int tabsel_123[2][3][16] = 
{ 
   { 
     {0,32,64,96,128,160,192,224,256,288,320,352,384,416,448,0}, 
     {0,32,48,56, 64, 80, 96,112,128,160,192,224,256,320,384,0}, 
     {0,32,40,48, 56, 64, 80, 96,112,128,160,192,224,256,320,0} 
   }, 
   { 
     {0,32,48,56,64,80,96,112,128,144,160,176,192,224,256,0}, 
     {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0}, 
     {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0} 
   } 
}; 
 
static const int freqs[9] = 
{ 
  44100, 48000, 32000, 
  22050, 24000, 16000, 
  11025, 12000, 8000 
}; 
 
/* 
 * decode a header and write the information 
 * into the frame structure 
 */ 
int decode_header(struct frame *fr, unsigned long header) 
{ 
  if (header & (1 << 20)) { 
    fr->lsf = (header & (1 << 19)) ? 0x0 : 0x1; 
    fr->mpeg25 = 0; 
  } 
  else { 
    fr->lsf = 1; 
    fr->mpeg25 = 1; 
  } 
 
  fr->lay = 4 - ((header >> 17) & 3); 
 
  if (((header >> 10) & 0x3) == 0x3) 
    return 0;     /* illegal sample rate frequency index */ 
 
  if (fr->mpeg25) 
    fr->sampling_frequency = 6 + ((header >> 10) & 0x3); 
  else 
    fr->sampling_frequency = ((header >> 10) & 0x3) + (fr->lsf * 3); 
 
  fr->sample_rate = freqs[fr->sampling_frequency]; 
  fr->error_protection = ((header >> 16) & 0x1) ^ 0x1; 
 
  fr->bitrate_index = ((header>>12)&0xf); 
  fr->padding   = ((header>>9)&0x1); 
  fr->extension = ((header>>8)&0x1); 
  fr->mode      = ((header>>6)&0x3); 
  fr->mode_ext  = ((header>>4)&0x3); 
  fr->copyright = ((header>>3)&0x1); 
  fr->original  = ((header>>2)&0x1); 
  fr->emphasis  = header & 0x3; 
 
  fr->stereo    = (fr->mode == MPG_MD_MONO) ? 1 : 2; 
 
	/* free format ought to report a 'not supported' */ 
	/* but afaik free format MPEG-audio is not used  */ 
	/* in video streams anyway... (?)                */ 
 
  if (!fr->bitrate_index || (fr->bitrate_index == 15)) 
    return 0;     /* free format not supported or bad format */ 
 
  /* calc size of the audio-frame (including        */ 
  /* an optional 16-bit CRC-sum, excluding header)  */ 
   
  switch (fr->lay) 
  { 
    case 1: 
      fr->framesize  = tabsel_123[fr->lsf][0][fr->bitrate_index] * 12000; 
      fr->framesize /= freqs[fr->sampling_frequency]; 
      fr->framesize  = ((fr->framesize+fr->padding) << 2) - 4; 
      break; 
    case 2: 
      fr->framesize  = tabsel_123[fr->lsf][1][fr->bitrate_index] * 144000; 
      fr->framesize /= freqs[fr->sampling_frequency]; 
      fr->framesize += fr->padding - 4; 
      break; 
    case 3: 
      fr->framesize  = tabsel_123[fr->lsf][2][fr->bitrate_index] * 144000; 
      fr->framesize /= freqs[fr->sampling_frequency] << (fr->lsf); 
      fr->framesize += fr->padding - 4; 
      break;  
    default: 
      return 0;     /* Unknown layer type */ 
  } 
  return fr->framesize; 
}