yading@10: /*
yading@10:  * MPEG Audio header decoder
yading@10:  * Copyright (c) 2001, 2002 Fabrice Bellard
yading@10:  *
yading@10:  * This file is part of FFmpeg.
yading@10:  *
yading@10:  * FFmpeg is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * FFmpeg is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with FFmpeg; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: /**
yading@10:  * @file
yading@10:  * MPEG Audio header decoder.
yading@10:  */
yading@10: 
yading@10: //#define DEBUG
yading@10: #include "avcodec.h"
yading@10: #include "mpegaudio.h"
yading@10: #include "mpegaudiodata.h"
yading@10: #include "mpegaudiodecheader.h"
yading@10: 
yading@10: 
yading@10: int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
yading@10: {
yading@10:     int sample_rate, frame_size, mpeg25, padding;
yading@10:     int sample_rate_index, bitrate_index;
yading@10:     if (header & (1<<20)) {
yading@10:         s->lsf = (header & (1<<19)) ? 0 : 1;
yading@10:         mpeg25 = 0;
yading@10:     } else {
yading@10:         s->lsf = 1;
yading@10:         mpeg25 = 1;
yading@10:     }
yading@10: 
yading@10:     s->layer = 4 - ((header >> 17) & 3);
yading@10:     /* extract frequency */
yading@10:     sample_rate_index = (header >> 10) & 3;
yading@10:     sample_rate = avpriv_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25);
yading@10:     sample_rate_index += 3 * (s->lsf + mpeg25);
yading@10:     s->sample_rate_index = sample_rate_index;
yading@10:     s->error_protection = ((header >> 16) & 1) ^ 1;
yading@10:     s->sample_rate = sample_rate;
yading@10: 
yading@10:     bitrate_index = (header >> 12) & 0xf;
yading@10:     padding = (header >> 9) & 1;
yading@10:     //extension = (header >> 8) & 1;
yading@10:     s->mode = (header >> 6) & 3;
yading@10:     s->mode_ext = (header >> 4) & 3;
yading@10:     //copyright = (header >> 3) & 1;
yading@10:     //original = (header >> 2) & 1;
yading@10:     //emphasis = header & 3;
yading@10: 
yading@10:     if (s->mode == MPA_MONO)
yading@10:         s->nb_channels = 1;
yading@10:     else
yading@10:         s->nb_channels = 2;
yading@10: 
yading@10:     if (bitrate_index != 0) {
yading@10:         frame_size = avpriv_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index];
yading@10:         s->bit_rate = frame_size * 1000;
yading@10:         switch(s->layer) {
yading@10:         case 1:
yading@10:             frame_size = (frame_size * 12000) / sample_rate;
yading@10:             frame_size = (frame_size + padding) * 4;
yading@10:             break;
yading@10:         case 2:
yading@10:             frame_size = (frame_size * 144000) / sample_rate;
yading@10:             frame_size += padding;
yading@10:             break;
yading@10:         default:
yading@10:         case 3:
yading@10:             frame_size = (frame_size * 144000) / (sample_rate << s->lsf);
yading@10:             frame_size += padding;
yading@10:             break;
yading@10:         }
yading@10:         s->frame_size = frame_size;
yading@10:     } else {
yading@10:         /* if no frame size computed, signal it */
yading@10:         return 1;
yading@10:     }
yading@10: 
yading@10: #if defined(DEBUG)
yading@10:     av_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ",
yading@10:            s->layer, s->sample_rate, s->bit_rate);
yading@10:     if (s->nb_channels == 2) {
yading@10:         if (s->layer == 3) {
yading@10:             if (s->mode_ext & MODE_EXT_MS_STEREO)
yading@10:                 av_dlog(NULL, "ms-");
yading@10:             if (s->mode_ext & MODE_EXT_I_STEREO)
yading@10:                 av_dlog(NULL, "i-");
yading@10:         }
yading@10:         av_dlog(NULL, "stereo");
yading@10:     } else {
yading@10:         av_dlog(NULL, "mono");
yading@10:     }
yading@10:     av_dlog(NULL, "\n");
yading@10: #endif
yading@10:     return 0;
yading@10: }
yading@10: 
yading@10: int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
yading@10: {
yading@10:     MPADecodeHeader s1, *s = &s1;
yading@10: 
yading@10:     if (ff_mpa_check_header(head) != 0)
yading@10:         return -1;
yading@10: 
yading@10:     if (avpriv_mpegaudio_decode_header(s, head) != 0) {
yading@10:         return -1;
yading@10:     }
yading@10: 
yading@10:     switch(s->layer) {
yading@10:     case 1:
yading@10:         avctx->codec_id = AV_CODEC_ID_MP1;
yading@10:         *frame_size = 384;
yading@10:         break;
yading@10:     case 2:
yading@10:         avctx->codec_id = AV_CODEC_ID_MP2;
yading@10:         *frame_size = 1152;
yading@10:         break;
yading@10:     default:
yading@10:     case 3:
yading@10:         avctx->codec_id = AV_CODEC_ID_MP3;
yading@10:         if (s->lsf)
yading@10:             *frame_size = 576;
yading@10:         else
yading@10:             *frame_size = 1152;
yading@10:         break;
yading@10:     }
yading@10: 
yading@10:     *sample_rate = s->sample_rate;
yading@10:     *channels = s->nb_channels;
yading@10:     *bit_rate = s->bit_rate;
yading@10:     return s->frame_size;
yading@10: }