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