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 info. Return -1 if error in
56 header, otherwise the coded frame size in bytes */
57 int ff_mpa_decode_header(uint32_t head, int *sample_rate,
58 int *channels, int *frame_size, int *bitrate, enum AVCodecID *codec_id);
59
60 /* fast header check for resync */
ff_mpa_check_header(uint32_t header)61 static inline int ff_mpa_check_header(uint32_t header){
62 /* header */
63 if ((header & 0xffe00000) != 0xffe00000)
64 return -1;
65 /* version check */
66 if ((header & (3<<19)) == 1<<19)
67 return -1;
68 /* layer check */
69 if ((header & (3<<17)) == 0)
70 return -1;
71 /* bit rate */
72 if ((header & (0xf<<12)) == 0xf<<12)
73 return -1;
74 /* frequency */
75 if ((header & (3<<10)) == 3<<10)
76 return -1;
77 return 0;
78 }
79
80 #endif /* AVCODEC_MPEGAUDIODECHEADER_H */
81