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, int* spf, int* mpa_layer, int* br){
  38     int stereo,ssize,lsf,framesize,padding,bitrate_index,sampling_frequency, divisor;
  39     int bitrate;
  40     int layer, mult[3] = { 12000, 144000, 144000 };
  41     unsigned long newhead =
  42       hbuf[0] << 24 |
  43       hbuf[1] << 16 |
  44       hbuf[2] <<  8 |
  45       hbuf[3];
  46
  47 //    printf("head=0x%08X\n",newhead);
  48
  49 #if 1
  50     // head_check:
  51     if( (newhead & 0xffe00000) != 0xffe00000 ){
  52         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"head_check failed\n");
  53         return -1;
  54     }
  55 #endif
  56
  57     layer = 4-((newhead>>17)&3);
  58     if(layer==4){
  59       mp_msg(MSGT_DEMUXER,MSGL_DBG2,"not layer-1/2/3\n");
  60       return -1;
  61     }
  62
  63     sampling_frequency = ((newhead>>10)&0x3);  // valid: 0..2
  64     if(sampling_frequency==3){
  65         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"invalid sampling_frequency\n");
  66         return -1;
  67     }
  68
  69     if( newhead & ((long)1<<20) ) {
  70       // MPEG 1.0 (lsf==0) or MPEG 2.0 (lsf==1)
  71       lsf = (newhead & ((long)1<<19)) ? 0x0 : 0x1;
  72       sampling_frequency += (lsf*3);
  73     } else {
  74       // MPEG 2.5
  75       lsf = 1;
  76       sampling_frequency += 6;
  77     }
  78
  79 //    crc = ((newhead>>16)&0x1)^0x1;
  80     bitrate_index = ((newhead>>12)&0xf);  // valid: 1..14
  81     padding   = ((newhead>>9)&0x1);
  82 //    fr->extension = ((newhead>>8)&0x1);
  83 //    fr->mode      = ((newhead>>6)&0x3);
  84 //    fr->mode_ext  = ((newhead>>4)&0x3);
  85 //    fr->copyright = ((newhead>>3)&0x1);
  86 //    fr->original  = ((newhead>>2)&0x1);
  87 //    fr->emphasis  = newhead & 0x3;
  88
  89     stereo    = ( (((newhead>>6)&0x3)) == 3) ? 1 : 2;
  90
  91 // !checked later through tabsel_123[]!
  92 //    if(!bitrate_index || bitrate_index==15){
  93 //      mp_msg(MSGT_DEMUXER,MSGL_DBG2,"Free format not supported.\n");
  94 //      return -1;
  95 //    }
  96
  97     if(lsf)
  98       ssize = (stereo == 1) ? 9 : 17;
  99     else
 100       ssize = (stereo == 1) ? 17 : 32;
 101     if(!((newhead>>16)&0x1)) ssize += 2; // CRC
 102
 103     bitrate = tabsel_123[lsf][layer-1][bitrate_index];
 104     framesize = bitrate * mult[layer-1];
 105
 106     mp_msg(MSGT_DEMUXER,MSGL_DBG2,"FRAMESIZE: %d, layer: %d, bitrate: %d, mult: %d\n",
 107         framesize, layer, tabsel_123[lsf][layer-1][bitrate_index], mult[layer-1]);
 108     if(!framesize){
 109         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"invalid framesize/bitrate_index\n");
 110         return -1;
 111     }
 112
 113     divisor = (layer == 3 ? (freqs[sampling_frequency] << lsf) : freqs[sampling_frequency]);
 114     framesize /= divisor;
 115     if(layer==1)
 116       framesize = (framesize+padding)*4;
 117     else
 118       framesize += padding;
 119
 120 //    if(framesize<=0 || framesize>MAXFRAMESIZE) return FALSE;
 121     if(srate) {
 122       *srate = freqs[sampling_frequency];
 123       if(spf) {
 124         if(layer == 1)
 125           *spf = 384;
 126         else if(layer == 2)
 127           *spf = 1152;
 128         else if(*srate < 32000)
 129           *spf = 576;
 130         else
 131           *spf = 1152;
 132       }
 133     }
 134     if(mpa_layer) *mpa_layer = layer;
 135     if(chans) *chans = stereo;
 136     if(br) *br = bitrate;
 137
 138     return framesize;
 139 }
 140