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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 "avcodec.h"
30 #include "internal.h"
31 #include "mpegaudio.h"
32 #include "mpegaudiodata.h"
33 #include "mpegaudiodecheader.h"
34 
35 
37 {
38  int sample_rate, frame_size, mpeg25, padding;
39  int sample_rate_index, bitrate_index;
40  int ret;
41 
42  ret = ff_mpa_check_header(header);
43  if (ret < 0)
44  return ret;
45 
46  if (header & (1<<20)) {
47  s->lsf = (header & (1<<19)) ? 0 : 1;
48  mpeg25 = 0;
49  } else {
50  s->lsf = 1;
51  mpeg25 = 1;
52  }
53 
54  s->layer = 4 - ((header >> 17) & 3);
55  /* extract frequency */
56  sample_rate_index = (header >> 10) & 3;
57  if (sample_rate_index >= FF_ARRAY_ELEMS(avpriv_mpa_freq_tab))
58  sample_rate_index = 0;
59  sample_rate = avpriv_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25);
60  sample_rate_index += 3 * (s->lsf + mpeg25);
61  s->sample_rate_index = sample_rate_index;
62  s->error_protection = ((header >> 16) & 1) ^ 1;
63  s->sample_rate = sample_rate;
64 
65  bitrate_index = (header >> 12) & 0xf;
66  padding = (header >> 9) & 1;
67  //extension = (header >> 8) & 1;
68  s->mode = (header >> 6) & 3;
69  s->mode_ext = (header >> 4) & 3;
70  //copyright = (header >> 3) & 1;
71  //original = (header >> 2) & 1;
72  //emphasis = header & 3;
73 
74  if (s->mode == MPA_MONO)
75  s->nb_channels = 1;
76  else
77  s->nb_channels = 2;
78 
79  if (bitrate_index != 0) {
80  frame_size = avpriv_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index];
81  s->bit_rate = frame_size * 1000;
82  switch(s->layer) {
83  case 1:
84  frame_size = (frame_size * 12000) / sample_rate;
85  frame_size = (frame_size + padding) * 4;
86  break;
87  case 2:
88  frame_size = (frame_size * 144000) / sample_rate;
89  frame_size += padding;
90  break;
91  default:
92  case 3:
93  frame_size = (frame_size * 144000) / (sample_rate << s->lsf);
94  frame_size += padding;
95  break;
96  }
97  s->frame_size = frame_size;
98  } else {
99  /* if no frame size computed, signal it */
100  return 1;
101  }
102 
103 #if defined(DEBUG)
104  ff_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ",
105  s->layer, s->sample_rate, s->bit_rate);
106  if (s->nb_channels == 2) {
107  if (s->layer == 3) {
108  if (s->mode_ext & MODE_EXT_MS_STEREO)
109  ff_dlog(NULL, "ms-");
110  if (s->mode_ext & MODE_EXT_I_STEREO)
111  ff_dlog(NULL, "i-");
112  }
113  ff_dlog(NULL, "stereo");
114  } else {
115  ff_dlog(NULL, "mono");
116  }
117  ff_dlog(NULL, "\n");
118 #endif
119  return 0;
120 }
121 
122 int ff_mpa_decode_header(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
123 {
124  MPADecodeHeader s1, *s = &s1;
125 
126  if (avpriv_mpegaudio_decode_header(s, head) != 0) {
127  return -1;
128  }
129 
130  switch(s->layer) {
131  case 1:
132  *codec_id = AV_CODEC_ID_MP1;
133  *frame_size = 384;
134  break;
135  case 2:
136  *codec_id = AV_CODEC_ID_MP2;
137  *frame_size = 1152;
138  break;
139  default:
140  case 3:
141  if (*codec_id != AV_CODEC_ID_MP3ADU)
142  *codec_id = AV_CODEC_ID_MP3;
143  if (s->lsf)
144  *frame_size = 576;
145  else
146  *frame_size = 1152;
147  break;
148  }
149 
150  *sample_rate = s->sample_rate;
151  *channels = s->nb_channels;
152  *bit_rate = s->bit_rate;
153  return s->frame_size;
154 }
155 
156 #if LIBAVCODEC_VERSION_MAJOR < 58
157 int avpriv_mpa_decode_header2(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
158 {
159  return ff_mpa_decode_header(head, sample_rate, channels, frame_size, bit_rate, codec_id);
160 }
161 
162 int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
163 {
164  return ff_mpa_decode_header(head, sample_rate, channels, frame_size, bit_rate, &avctx->codec_id);
165 }
166 #endif
#define NULL
Definition: coverity.c:32
const char * s
Definition: avisynth_c.h:631
enum AVCodecID codec_id
Definition: ffmpeg_vaapi.c:149
mpeg audio layer common tables.
const uint16_t avpriv_mpa_freq_tab[3]
Definition: mpegaudiodata.c:40
int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
#define ff_dlog(a,...)
static const uint8_t header[24]
Definition: sdr2.c:67
AVCodecID
Identify the syntax and semantics of the bitstream.
Definition: avcodec.h:189
#define MODE_EXT_MS_STEREO
Definition: mpegaudiodata.h:34
preferred ID for decoding MPEG audio layer 1, 2 or 3
Definition: avcodec.h:515
static int ff_mpa_check_header(uint32_t header)
int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
#define FF_ARRAY_ELEMS(a)
int avpriv_mpa_decode_header2(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
sample_rate
int frame_size
Definition: mxfenc.c:1821
Libavcodec external API header.
enum AVCodecID codec_id
Definition: avcodec.h:1674
main external API structure.
Definition: avcodec.h:1657
#define MODE_EXT_I_STEREO
Definition: mpegaudiodata.h:35
#define MPA_MONO
Definition: mpegaudio.h:48
#define s1
Definition: regdef.h:38
MPEG Audio header decoder.
common internal api header.
common internal and external API header
mpeg audio declarations for both encoder and decoder.
int ff_mpa_decode_header(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
const uint16_t avpriv_mpa_bitrate_tab[2][3][15]
Definition: mpegaudiodata.c:30