1/* 2 * MPEG Audio header decoder 3 * Copyright (c) 2001, 2002 Fabrice Bellard 4 * 5 * This file is part of Libav. 6 * 7 * Libav is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Lesser General Public 9 * License as published by the Free Software Foundation; either 10 * version 2.1 of the License, or (at your option) any later version. 11 * 12 * Libav is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License along with Libav; if not, write to the Free Software 19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 20 */ 21 22/** 23 * @file 24 * MPEG Audio header decoder. 25 */ 26 27#ifndef AVCODEC_MPEGAUDIODECHEADER_H 28#define AVCODEC_MPEGAUDIODECHEADER_H 29 30#include "avcodec.h" 31 32#define MP3_MASK 0xFFFE0CCF 33 34#define MPA_DECODE_HEADER \ 35 int frame_size; \ 36 int error_protection; \ 37 int layer; \ 38 int sample_rate; \ 39 int sample_rate_index; /* between 0 and 8 */ \ 40 int bit_rate; \ 41 int nb_channels; \ 42 int mode; \ 43 int mode_ext; \ 44 int lsf; 45 46typedef struct MPADecodeHeader { 47 MPA_DECODE_HEADER 48} MPADecodeHeader; 49 50/* header decoding. MUST check the header before because no 51 consistency check is done there. Return 1 if free format found and 52 that the frame size must be computed externally */ 53int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header); 54 55/* useful helper to get mpeg audio stream infos. Return -1 if error in 56 header, otherwise the coded frame size in bytes */ 57int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bitrate); 58 59/* fast header check for resync */ 60static inline int ff_mpa_check_header(uint32_t header){ 61 /* header */ 62 if ((header & 0xffe00000) != 0xffe00000) 63 return -1; 64 /* layer check */ 65 if ((header & (3<<17)) == 0) 66 return -1; 67 /* bit rate */ 68 if ((header & (0xf<<12)) == 0xf<<12) 69 return -1; 70 /* frequency */ 71 if ((header & (3<<10)) == 3<<10) 72 return -1; 73 return 0; 74} 75 76#endif /* AVCODEC_MPEGAUDIODECHEADER_H */ 77