mpegaudiodecheader.h (2449B)
1 /* 2 * MPEG Audio header decoder 3 * Copyright (c) 2001, 2002 Fabrice Bellard 4 * 5 * This file is part of FFmpeg. 6 * 7 * FFmpeg 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 * FFmpeg 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 FFmpeg; 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 <stdint.h> 31 #include "codec_id.h" 32 33 #define MP3_MASK 0xFFFE0CCF 34 35 #define MPA_DECODE_HEADER \ 36 int frame_size; \ 37 int error_protection; \ 38 int layer; \ 39 int sample_rate; \ 40 int sample_rate_index; /* between 0 and 8 */ \ 41 int bit_rate; \ 42 int nb_channels; \ 43 int mode; \ 44 int mode_ext; \ 45 int lsf; 46 47 typedef struct MPADecodeHeader { 48 MPA_DECODE_HEADER 49 } MPADecodeHeader; 50 51 /* header decoding. MUST check the header before because no 52 consistency check is done there. Return 1 if free format found and 53 that the frame size must be computed externally */ 54 int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header); 55 56 /* useful helper to get MPEG audio stream info. Return -1 if error in 57 header, otherwise the coded frame size in bytes */ 58 int ff_mpa_decode_header(uint32_t head, int *sample_rate, 59 int *channels, int *frame_size, int *bitrate, enum AVCodecID *codec_id); 60 61 /* fast header check for resync */ 62 static inline int ff_mpa_check_header(uint32_t header){ 63 /* header */ 64 if ((header & 0xffe00000) != 0xffe00000) 65 return -1; 66 /* version check */ 67 if ((header & (3<<19)) == 1<<19) 68 return -1; 69 /* layer check */ 70 if ((header & (3<<17)) == 0) 71 return -1; 72 /* bit rate */ 73 if ((header & (0xf<<12)) == 0xf<<12) 74 return -1; 75 /* frequency */ 76 if ((header & (3<<10)) == 3<<10) 77 return -1; 78 return 0; 79 } 80 81 #endif /* AVCODEC_MPEGAUDIODECHEADER_H */