00001 /* 00002 * MPEG Audio header decoder 00003 * Copyright (c) 2001, 2002 Fabrice Bellard 00004 * 00005 * This file is part of FFmpeg. 00006 * 00007 * FFmpeg is free software; you can redistribute it and/or 00008 * modify it under the terms of the GNU Lesser General Public 00009 * License as published by the Free Software Foundation; either 00010 * version 2.1 of the License, or (at your option) any later version. 00011 * 00012 * FFmpeg is distributed in the hope that it will be useful, 00013 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00014 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00015 * Lesser General Public License for more details. 00016 * 00017 * You should have received a copy of the GNU Lesser General Public 00018 * License along with FFmpeg; if not, write to the Free Software 00019 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 00020 */ 00021 00027 //#define DEBUG 00028 #include "avcodec.h" 00029 #include "mpegaudio.h" 00030 #include "mpegaudiodata.h" 00031 #include "mpegaudiodecheader.h" 00032 00033 00034 int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header) 00035 { 00036 int sample_rate, frame_size, mpeg25, padding; 00037 int sample_rate_index, bitrate_index; 00038 if (header & (1<<20)) { 00039 s->lsf = (header & (1<<19)) ? 0 : 1; 00040 mpeg25 = 0; 00041 } else { 00042 s->lsf = 1; 00043 mpeg25 = 1; 00044 } 00045 00046 s->layer = 4 - ((header >> 17) & 3); 00047 /* extract frequency */ 00048 sample_rate_index = (header >> 10) & 3; 00049 sample_rate = avpriv_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25); 00050 sample_rate_index += 3 * (s->lsf + mpeg25); 00051 s->sample_rate_index = sample_rate_index; 00052 s->error_protection = ((header >> 16) & 1) ^ 1; 00053 s->sample_rate = sample_rate; 00054 00055 bitrate_index = (header >> 12) & 0xf; 00056 padding = (header >> 9) & 1; 00057 //extension = (header >> 8) & 1; 00058 s->mode = (header >> 6) & 3; 00059 s->mode_ext = (header >> 4) & 3; 00060 //copyright = (header >> 3) & 1; 00061 //original = (header >> 2) & 1; 00062 //emphasis = header & 3; 00063 00064 if (s->mode == MPA_MONO) 00065 s->nb_channels = 1; 00066 else 00067 s->nb_channels = 2; 00068 00069 if (bitrate_index != 0) { 00070 frame_size = avpriv_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index]; 00071 s->bit_rate = frame_size * 1000; 00072 switch(s->layer) { 00073 case 1: 00074 frame_size = (frame_size * 12000) / sample_rate; 00075 frame_size = (frame_size + padding) * 4; 00076 break; 00077 case 2: 00078 frame_size = (frame_size * 144000) / sample_rate; 00079 frame_size += padding; 00080 break; 00081 default: 00082 case 3: 00083 frame_size = (frame_size * 144000) / (sample_rate << s->lsf); 00084 frame_size += padding; 00085 break; 00086 } 00087 s->frame_size = frame_size; 00088 } else { 00089 /* if no frame size computed, signal it */ 00090 return 1; 00091 } 00092 00093 #if defined(DEBUG) 00094 av_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ", 00095 s->layer, s->sample_rate, s->bit_rate); 00096 if (s->nb_channels == 2) { 00097 if (s->layer == 3) { 00098 if (s->mode_ext & MODE_EXT_MS_STEREO) 00099 av_dlog(NULL, "ms-"); 00100 if (s->mode_ext & MODE_EXT_I_STEREO) 00101 av_dlog(NULL, "i-"); 00102 } 00103 av_dlog(NULL, "stereo"); 00104 } else { 00105 av_dlog(NULL, "mono"); 00106 } 00107 av_dlog(NULL, "\n"); 00108 #endif 00109 return 0; 00110 } 00111 00112 int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate) 00113 { 00114 MPADecodeHeader s1, *s = &s1; 00115 00116 if (ff_mpa_check_header(head) != 0) 00117 return -1; 00118 00119 if (avpriv_mpegaudio_decode_header(s, head) != 0) { 00120 return -1; 00121 } 00122 00123 switch(s->layer) { 00124 case 1: 00125 avctx->codec_id = CODEC_ID_MP1; 00126 *frame_size = 384; 00127 break; 00128 case 2: 00129 avctx->codec_id = CODEC_ID_MP2; 00130 *frame_size = 1152; 00131 break; 00132 default: 00133 case 3: 00134 avctx->codec_id = CODEC_ID_MP3; 00135 if (s->lsf) 00136 *frame_size = 576; 00137 else 00138 *frame_size = 1152; 00139 break; 00140 } 00141 00142 *sample_rate = s->sample_rate; 00143 *channels = s->nb_channels; 00144 *bit_rate = s->bit_rate; 00145 avctx->sub_id = s->layer; 00146 return s->frame_size; 00147 }