mpegaudio_parser.c 4.22 KB
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/*
 * MPEG Audio parser
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 * Copyright (c) 2003 Fabrice Bellard
 * Copyright (c) 2003 Michael Niedermayer
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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
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
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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
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * 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
 */

#include "parser.h"
#include "mpegaudio.h"
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#include "mpegaudiodecheader.h"
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typedef struct MpegAudioParseContext {
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    ParseContext pc;
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    int frame_size;
    uint32_t header;
    int header_count;
} MpegAudioParseContext;

#define MPA_HEADER_SIZE 4

/* header + layer + bitrate + freq + lsf/mpeg25 */
#undef SAME_HEADER_MASK /* mpegaudio.h defines different version */
#define SAME_HEADER_MASK \
   (0xffe00000 | (3 << 17) | (3 << 10) | (3 << 19))

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/* useful helper to get mpeg audio stream infos. Return -1 if error in
   header, otherwise the coded frame size in bytes */
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int ff_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
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{
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    MPADecodeHeader s1, *s = &s1;
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    if (ff_mpa_check_header(head) != 0)
        return -1;

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    if (ff_mpegaudio_decode_header(s, head) != 0) {
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        return -1;
    }

    switch(s->layer) {
    case 1:
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        avctx->codec_id = CODEC_ID_MP1;
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        *frame_size = 384;
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        break;
    case 2:
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        avctx->codec_id = CODEC_ID_MP2;
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        *frame_size = 1152;
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        break;
    default:
    case 3:
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        avctx->codec_id = CODEC_ID_MP3;
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        if (s->lsf)
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            *frame_size = 576;
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        else
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            *frame_size = 1152;
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        break;
    }

    *sample_rate = s->sample_rate;
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    *channels = s->nb_channels;
    *bit_rate = s->bit_rate;
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    avctx->sub_id = s->layer;
    return s->frame_size;
}

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static int mpegaudio_parse(AVCodecParserContext *s1,
                           AVCodecContext *avctx,
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                           const uint8_t **poutbuf, int *poutbuf_size,
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                           const uint8_t *buf, int buf_size)
{
    MpegAudioParseContext *s = s1->priv_data;
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    ParseContext *pc = &s->pc;
    uint32_t state= pc->state;
    int i;
    int next= END_NOT_FOUND;

    for(i=0; i<buf_size; ){
        if(s->frame_size){
            int inc= FFMIN(buf_size - i, s->frame_size);
            i += inc;
            s->frame_size -= inc;

            if(!s->frame_size){
                next= i;
                break;
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            }
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        }else{
            while(i<buf_size){
                int ret, sr, channels, bit_rate, frame_size;

                state= (state<<8) + buf[i++];
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                ret = ff_mpa_decode_header(avctx, state, &sr, &channels, &frame_size, &bit_rate);
                if (ret < 4) {
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                    s->header_count= -2;
                } else {
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                    if((state&SAME_HEADER_MASK) != (s->header&SAME_HEADER_MASK) && s->header)
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                        s->header_count= -3;
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                    s->header= state;
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                    s->header_count++;
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                    s->frame_size = ret-4;
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                    if(s->header_count > 1){
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                        avctx->sample_rate= sr;
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                        avctx->channels   = channels;
                        avctx->frame_size = frame_size;
                        avctx->bit_rate   = bit_rate;
                    }
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                    break;
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                }
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            }
        }
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    }
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    pc->state= state;
    if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
        *poutbuf = NULL;
        *poutbuf_size = 0;
        return buf_size;
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    }
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    *poutbuf = buf;
    *poutbuf_size = buf_size;
    return next;
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}


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AVCodecParser ff_mpegaudio_parser = {
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    { CODEC_ID_MP1, CODEC_ID_MP2, CODEC_ID_MP3 },
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    sizeof(MpegAudioParseContext),
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    NULL,
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    mpegaudio_parse,
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    ff_parse_close,
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};