libmpdemux/mp3_hdr.c

   1 #include <stdio.h>
   2
   3 #include "config.h"
   4 #include "../mp_msg.h"
   5
   6 //----------------------- mp3 audio frame header parser -----------------------
   7
   8 static int tabsel_123[2][3][16] = {
   9    { {0,32,64,96,128,160,192,224,256,288,320,352,384,416,448,0},
  10      {0,32,48,56, 64, 80, 96,112,128,160,192,224,256,320,384,0},
  11      {0,32,40,48, 56, 64, 80, 96,112,128,160,192,224,256,320,0} },
  12
  13    { {0,32,48,56,64,80,96,112,128,144,160,176,192,224,256,0},
  14      {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0},
  15      {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0} }
  16 };
  17
  18 static long freqs[9] = { 44100, 48000, 32000,   // MPEG 1.0
  19                          22050, 24000, 16000,   // MPEG 2.0
  20                          11025, 12000,  8000};  // MPEG 2.5
  21
  22 int mp_mp3_get_lsf(unsigned char* hbuf){
  23     unsigned long newhead =
  24       hbuf[0] << 24 |
  25       hbuf[1] << 16 |
  26       hbuf[2] <<  8 |
  27       hbuf[3];
  28     if( newhead & ((long)1<<20) ) {
  29       return (newhead & ((long)1<<19)) ? 0x0 : 0x1;
  30     }
  31     return 1;
  32 }
  33
  34 /*
  35  * return frame size or -1 (bad frame)
  36  */
  37 int mp_get_mp3_header(unsigned char* hbuf,int* chans, int* srate){
  38     int stereo,ssize,lsf,framesize,padding,bitrate_index,sampling_frequency;
  39     unsigned long newhead =
  40       hbuf[0] << 24 |
  41       hbuf[1] << 16 |
  42       hbuf[2] <<  8 |
  43       hbuf[3];
  44
  45 //    printf("head=0x%08X\n",newhead);
  46
  47 #if 1
  48     // head_check:
  49     if( (newhead & 0xffe00000) != 0xffe00000 ){
  50         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"head_check failed\n");
  51         return -1;
  52     }
  53 #endif
  54
  55     if((4-((newhead>>17)&3))!=3){
  56       mp_msg(MSGT_DEMUXER,MSGL_DBG2,"not layer-3\n");
  57       return -1;
  58     }
  59
  60     sampling_frequency = ((newhead>>10)&0x3);  // valid: 0..2
  61     if(sampling_frequency==3){
  62         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"invalid sampling_frequency\n");
  63         return -1;
  64     }
  65
  66     if( newhead & ((long)1<<20) ) {
  67       // MPEG 1.0 (lsf==0) or MPEG 2.0 (lsf==1)
  68       lsf = (newhead & ((long)1<<19)) ? 0x0 : 0x1;
  69       sampling_frequency += (lsf*3);
  70     } else {
  71       // MPEG 2.5
  72       lsf = 1;
  73       sampling_frequency += 6;
  74     }
  75
  76 //    crc = ((newhead>>16)&0x1)^0x1;
  77     bitrate_index = ((newhead>>12)&0xf);  // valid: 1..14
  78     padding   = ((newhead>>9)&0x1);
  79 //    fr->extension = ((newhead>>8)&0x1);
  80 //    fr->mode      = ((newhead>>6)&0x3);
  81 //    fr->mode_ext  = ((newhead>>4)&0x3);
  82 //    fr->copyright = ((newhead>>3)&0x1);
  83 //    fr->original  = ((newhead>>2)&0x1);
  84 //    fr->emphasis  = newhead & 0x3;
  85
  86     stereo    = ( (((newhead>>6)&0x3)) == 3) ? 1 : 2;
  87
  88 // !checked later through tabsel_123[]!
  89 //    if(!bitrate_index || bitrate_index==15){
  90 //      mp_msg(MSGT_DEMUXER,MSGL_DBG2,"Free format not supported.\n");
  91 //      return -1;
  92 //    }
  93
  94     if(lsf)
  95       ssize = (stereo == 1) ? 9 : 17;
  96     else
  97       ssize = (stereo == 1) ? 17 : 32;
  98     if(!((newhead>>16)&0x1)) ssize += 2; // CRC
  99
 100     framesize = tabsel_123[lsf][2][bitrate_index] * 144000;
 101
 102     if(!framesize){
 103         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"invalid framesize/bitrate_index\n");
 104         return -1;
 105     }
 106
 107     framesize /= freqs[sampling_frequency]<<lsf;
 108     framesize += padding;
 109
 110 //    if(framesize<=0 || framesize>MAXFRAMESIZE) return FALSE;
 111     if(srate) *srate = freqs[sampling_frequency];
 112     if(chans) *chans = stereo;
 113
 114     return framesize;
 115 }
 116