FFmpeg
mpegaudiodecheader.c
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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 #include "libavutil/common.h"
28 
29 #include "mpegaudio.h"
30 #include "mpegaudiodata.h"
31 #include "mpegaudiodecheader.h"
32 
33 
35 {
36  int sample_rate, frame_size, mpeg25, padding;
37  int sample_rate_index, bitrate_index;
38  int ret;
39 
41  if (ret < 0)
42  return ret;
43 
44  if (header & (1<<20)) {
45  s->lsf = (header & (1<<19)) ? 0 : 1;
46  mpeg25 = 0;
47  } else {
48  s->lsf = 1;
49  mpeg25 = 1;
50  }
51 
52  s->layer = 4 - ((header >> 17) & 3);
53  /* extract frequency */
54  sample_rate_index = (header >> 10) & 3;
55  if (sample_rate_index >= FF_ARRAY_ELEMS(avpriv_mpa_freq_tab))
56  sample_rate_index = 0;
57  sample_rate = avpriv_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25);
58  sample_rate_index += 3 * (s->lsf + mpeg25);
59  s->sample_rate_index = sample_rate_index;
60  s->error_protection = ((header >> 16) & 1) ^ 1;
61  s->sample_rate = sample_rate;
62 
63  bitrate_index = (header >> 12) & 0xf;
64  padding = (header >> 9) & 1;
65  //extension = (header >> 8) & 1;
66  s->mode = (header >> 6) & 3;
67  s->mode_ext = (header >> 4) & 3;
68  //copyright = (header >> 3) & 1;
69  //original = (header >> 2) & 1;
70  //emphasis = header & 3;
71 
72  if (s->mode == MPA_MONO)
73  s->nb_channels = 1;
74  else
75  s->nb_channels = 2;
76 
77  if (bitrate_index != 0) {
78  frame_size = avpriv_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index];
79  s->bit_rate = frame_size * 1000;
80  switch(s->layer) {
81  case 1:
82  frame_size = (frame_size * 12000) / sample_rate;
83  frame_size = (frame_size + padding) * 4;
84  break;
85  case 2:
86  frame_size = (frame_size * 144000) / sample_rate;
87  frame_size += padding;
88  break;
89  default:
90  case 3:
91  frame_size = (frame_size * 144000) / (sample_rate << s->lsf);
92  frame_size += padding;
93  break;
94  }
95  s->frame_size = frame_size;
96  } else {
97  /* if no frame size computed, signal it */
98  return 1;
99  }
100 
101 #if defined(DEBUG)
102  ff_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ",
103  s->layer, s->sample_rate, s->bit_rate);
104  if (s->nb_channels == 2) {
105  if (s->layer == 3) {
106  if (s->mode_ext & MODE_EXT_MS_STEREO)
107  ff_dlog(NULL, "ms-");
108  if (s->mode_ext & MODE_EXT_I_STEREO)
109  ff_dlog(NULL, "i-");
110  }
111  ff_dlog(NULL, "stereo");
112  } else {
113  ff_dlog(NULL, "mono");
114  }
115  ff_dlog(NULL, "\n");
116 #endif
117  return 0;
118 }
119 
120 int ff_mpa_decode_header(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
121 {
122  MPADecodeHeader s1, *s = &s1;
123 
124  if (avpriv_mpegaudio_decode_header(s, head) != 0) {
125  return -1;
126  }
127 
128  switch(s->layer) {
129  case 1:
131  *frame_size = 384;
132  break;
133  case 2:
135  *frame_size = 1152;
136  break;
137  default:
138  case 3:
141  if (s->lsf)
142  *frame_size = 576;
143  else
144  *frame_size = 1152;
145  break;
146  }
147 
148  *sample_rate = s->sample_rate;
149  *channels = s->nb_channels;
150  *bit_rate = s->bit_rate;
151  return s->frame_size;
152 }
MPA_MONO
#define MPA_MONO
Definition: mpegaudio.h:49
avpriv_mpa_freq_tab
const uint16_t avpriv_mpa_freq_tab[3]
Definition: mpegaudiodata.c:40
avpriv_mpa_bitrate_tab
const uint16_t avpriv_mpa_bitrate_tab[2][3][15]
Definition: mpegaudiodata.c:30
mpegaudiodecheader.h
MPADecodeHeader
Definition: mpegaudiodecheader.h:47
sample_rate
sample_rate
Definition: ffmpeg_filter.c:156
AV_CODEC_ID_MP3ADU
@ AV_CODEC_ID_MP3ADU
Definition: codec_id.h:435
ff_mpa_decode_header
int ff_mpa_decode_header(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
Definition: mpegaudiodecheader.c:120
AV_CODEC_ID_MP3
@ AV_CODEC_ID_MP3
preferred ID for decoding MPEG audio layer 1, 2 or 3
Definition: codec_id.h:423
avpriv_mpegaudio_decode_header
int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
Definition: mpegaudiodecheader.c:34
FF_ARRAY_ELEMS
#define FF_ARRAY_ELEMS(a)
Definition: sinewin_tablegen.c:29
MODE_EXT_MS_STEREO
#define MODE_EXT_MS_STEREO
Definition: mpegaudiodata.h:37
s
#define s(width, name)
Definition: cbs_vp9.c:257
frame_size
int frame_size
Definition: mxfenc.c:2206
AV_CODEC_ID_MP2
@ AV_CODEC_ID_MP2
Definition: codec_id.h:422
s1
#define s1
Definition: regdef.h:38
channels
channels
Definition: aptx.h:33
codec_id
enum AVCodecID codec_id
Definition: vaapi_decode.c:369
NULL
#define NULL
Definition: coverity.c:32
AVCodecID
AVCodecID
Identify the syntax and semantics of the bitstream.
Definition: codec_id.h:47
ff_dlog
#define ff_dlog(a,...)
Definition: tableprint_vlc.h:29
ff_mpa_check_header
static int ff_mpa_check_header(uint32_t header)
Definition: mpegaudiodecheader.h:62
header
static const uint8_t header[24]
Definition: sdr2.c:67
common.h
xf
#define xf(width, name, var, range_min, range_max, subs,...)
Definition: cbs_av1.c:664
mpegaudio.h
ret
ret
Definition: filter_design.txt:187
MODE_EXT_I_STEREO
#define MODE_EXT_I_STEREO
Definition: mpegaudiodata.h:38
mpegaudiodata.h
AV_CODEC_ID_MP1
@ AV_CODEC_ID_MP1
Definition: codec_id.h:464