FFmpeg/libavcodec/mpegaudiodecheader.h

/*
 * MPEG Audio header decoder
 * Copyright (c) 2001, 2002 Fabrice Bellard
 *
 * This file is part of Libav.
 *
 * Libav is free software; you can redistribute it and/or
 * 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.
 *
 * Libav is distributed in the hope that it will be useful,
 * 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
 * License along with Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file
 * MPEG Audio header decoder.
 */

#ifndef AVCODEC_MPEGAUDIODECHEADER_H
#define AVCODEC_MPEGAUDIODECHEADER_H

#include "avcodec.h"

#define MP3_MASK 0xFFFE0CCF

#define MPA_DECODE_HEADER \
    int frame_size; \
    int error_protection; \
    int layer; \
    int sample_rate; \
    int sample_rate_index; /* between 0 and 8 */ \
    int bit_rate; \
    int nb_channels; \
    int mode; \
    int mode_ext; \
    int lsf;

typedef struct MPADecodeHeader {
  MPA_DECODE_HEADER
} MPADecodeHeader;

/* header decoding. MUST check the header before because no
   consistency check is done there. Return 1 if free format found and
   that the frame size must be computed externally */
int ff_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header);

/* useful helper to get mpeg audio stream infos. Return -1 if error in
   header, otherwise the coded frame size in bytes */
int ff_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bitrate);

/* fast header check for resync */
static inline int ff_mpa_check_header(uint32_t header){
    /* header */
    if ((header & 0xffe00000) != 0xffe00000)
        return -1;
    /* layer check */
    if ((header & (3<<17)) == 0)
        return -1;
    /* bit rate */
    if ((header & (0xf<<12)) == 0xf<<12)
        return -1;
    /* frequency */
    if ((header & (3<<10)) == 3<<10)
        return -1;
    return 0;
}

#endif /* AVCODEC_MPEGAUDIODECHEADER_H */