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  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 "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.  
  46. typedef 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 */
  53. int 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 */
  57. int 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 */
  60. static 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.