libmpdemux/mp3_hdr.c

   1 #include <stdio.h>
   2
   3 #include "config.h"
   4 #include "mp3_hdr.h"
   5 #include "mp_msg.h"
   6
   7 //----------------------- mp3 audio frame header parser -----------------------
   8
   9 static int tabsel_123[2][3][16] = {
  10    { {0,32,64,96,128,160,192,224,256,288,320,352,384,416,448,0},
  11      {0,32,48,56, 64, 80, 96,112,128,160,192,224,256,320,384,0},
  12      {0,32,40,48, 56, 64, 80, 96,112,128,160,192,224,256,320,0} },
  13
  14    { {0,32,48,56,64,80,96,112,128,144,160,176,192,224,256,0},
  15      {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0},
  16      {0,8,16,24,32,40,48,56,64,80,96,112,128,144,160,0} }
  17 };
  18
  19 static long freqs[9] = { 44100, 48000, 32000,   // MPEG 1.0
  20                          22050, 24000, 16000,   // MPEG 2.0
  21                          11025, 12000,  8000};  // MPEG 2.5
  22
  23 static int mp_mp3_get_lsf(unsigned char* hbuf){
  24     unsigned long newhead =
  25       hbuf[0] << 24 |
  26       hbuf[1] << 16 |
  27       hbuf[2] <<  8 |
  28       hbuf[3];
  29     if( newhead & ((long)1<<20) ) {
  30       return (newhead & ((long)1<<19)) ? 0x0 : 0x1;
  31     }
  32     return 1;
  33 }
  34
  35 /*
  36  * return frame size or -1 (bad frame)
  37  */
  38 int mp_get_mp3_header(unsigned char* hbuf,int* chans, int* srate, int* spf, int* mpa_layer, int* br){
  39     int stereo,ssize,lsf,framesize,padding,bitrate_index,sampling_frequency, divisor;
  40     int bitrate;
  41     int layer, mult[3] = { 12000, 144000, 144000 };
  42     unsigned long newhead =
  43       hbuf[0] << 24 |
  44       hbuf[1] << 16 |
  45       hbuf[2] <<  8 |
  46       hbuf[3];
  47
  48 //    printf("head=0x%08X\n",newhead);
  49
  50 #if 1
  51     // head_check:
  52     if( (newhead & 0xffe00000) != 0xffe00000 ){
  53         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"head_check failed\n");
  54         return -1;
  55     }
  56 #endif
  57
  58     layer = 4-((newhead>>17)&3);
  59     if(layer==4){
  60       mp_msg(MSGT_DEMUXER,MSGL_DBG2,"not layer-1/2/3\n");
  61       return -1;
  62     }
  63
  64     sampling_frequency = ((newhead>>10)&0x3);  // valid: 0..2
  65     if(sampling_frequency==3){
  66         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"invalid sampling_frequency\n");
  67         return -1;
  68     }
  69
  70     if( newhead & ((long)1<<20) ) {
  71       // MPEG 1.0 (lsf==0) or MPEG 2.0 (lsf==1)
  72       lsf = (newhead & ((long)1<<19)) ? 0x0 : 0x1;
  73       sampling_frequency += (lsf*3);
  74     } else {
  75       // MPEG 2.5
  76       lsf = 1;
  77       sampling_frequency += 6;
  78     }
  79
  80 //    crc = ((newhead>>16)&0x1)^0x1;
  81     bitrate_index = ((newhead>>12)&0xf);  // valid: 1..14
  82     padding   = ((newhead>>9)&0x1);
  83 //    fr->extension = ((newhead>>8)&0x1);
  84 //    fr->mode      = ((newhead>>6)&0x3);
  85 //    fr->mode_ext  = ((newhead>>4)&0x3);
  86 //    fr->copyright = ((newhead>>3)&0x1);
  87 //    fr->original  = ((newhead>>2)&0x1);
  88 //    fr->emphasis  = newhead & 0x3;
  89
  90     stereo    = ( (((newhead>>6)&0x3)) == 3) ? 1 : 2;
  91
  92 // !checked later through tabsel_123[]!
  93 //    if(!bitrate_index || bitrate_index==15){
  94 //      mp_msg(MSGT_DEMUXER,MSGL_DBG2,"Free format not supported.\n");
  95 //      return -1;
  96 //    }
  97
  98     if(lsf)
  99       ssize = (stereo == 1) ? 9 : 17;
 100     else
 101       ssize = (stereo == 1) ? 17 : 32;
 102     if(!((newhead>>16)&0x1)) ssize += 2; // CRC
 103
 104     bitrate = tabsel_123[lsf][layer-1][bitrate_index];
 105     framesize = bitrate * mult[layer-1];
 106
 107     mp_msg(MSGT_DEMUXER,MSGL_DBG2,"FRAMESIZE: %d, layer: %d, bitrate: %d, mult: %d\n",
 108         framesize, layer, tabsel_123[lsf][layer-1][bitrate_index], mult[layer-1]);
 109     if(!framesize){
 110         mp_msg(MSGT_DEMUXER,MSGL_DBG2,"invalid framesize/bitrate_index\n");
 111         return -1;
 112     }
 113
 114     divisor = (layer == 3 ? (freqs[sampling_frequency] << lsf) : freqs[sampling_frequency]);
 115     framesize /= divisor;
 116     if(layer==1)
 117       framesize = (framesize+padding)*4;
 118     else
 119       framesize += padding;
 120
 121 //    if(framesize<=0 || framesize>MAXFRAMESIZE) return FALSE;
 122     if(srate) {
 123       *srate = freqs[sampling_frequency];
 124       if(spf) {
 125         if(layer == 1)
 126           *spf = 384;
 127         else if(layer == 2)
 128           *spf = 1152;
 129         else if(*srate < 32000)
 130           *spf = 576;
 131         else
 132           *spf = 1152;
 133       }
 134     }
 135     if(mpa_layer) *mpa_layer = layer;
 136     if(chans) *chans = stereo;
 137     if(br) *br = bitrate;
 138
 139     return framesize;
 140 }
 141