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
avpriv_mpegaudio_decode_header(MPADecodeHeader * s,uint32_t header)36 int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
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
ff_mpa_decode_header(uint32_t head,int * sample_rate,int * channels,int * frame_size,int * bit_rate,enum AVCodecID * codec_id)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