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ffmpeg / libavcodec / mpegaudiodecheader.c @ 2912e87a

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/*
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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 Libav.
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 *
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 * Libav 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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 * Libav 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 Libav; 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
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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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#include "mpegaudiodecheader.h"
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int ff_mpegaudio_decode_header(MPADecodeHeader *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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    av_dlog(NULL, "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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                av_dlog(NULL, "ms-");
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            if (s->mode_ext & MODE_EXT_I_STEREO)
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                av_dlog(NULL, "i-");
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        }
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        av_dlog(NULL, "stereo");
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    } else {
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        av_dlog(NULL, "mono");
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    }
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    av_dlog(NULL, "\n");
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#endif
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    return 0;
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}