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
28
32
33
35 {
37 int sample_rate_index, bitrate_index;
39
43
45 s->lsf = (
header & (1<<19)) ? 0 : 1;
46 mpeg25 = 0;
47 } else {
49 mpeg25 = 1;
50 }
51
52 s->layer = 4 - ((
header >> 17) & 3);
53 /* extract frequency */
54 sample_rate_index = (
header >> 10) & 3;
56 sample_rate_index = 0;
58 sample_rate_index += 3 * (
s->lsf + mpeg25);
59 s->sample_rate_index = sample_rate_index;
60 s->error_protection = ((
header >> 16) & 1) ^ 1;
62
63 bitrate_index = (
header >> 12) & 0
xf;
64 padding = (
header >> 9) & 1;
65 //extension = (header >> 8) & 1;
67 s->mode_ext = (
header >> 4) & 3;
68 //copyright = (header >> 3) & 1;
69 //original = (header >> 2) & 1;
70 //emphasis = header & 3;
71
74 else
76
77 if (bitrate_index != 0) {
81 case 1:
84 break;
85 case 2:
88 break;
89 default:
90 case 3:
93 break;
94 }
96 } else {
97 /* if no frame size computed, signal it */
98 return 1;
99 }
100
101 #if defined(DEBUG)
103 s->layer,
s->sample_rate,
s->bit_rate);
104 if (
s->nb_channels == 2) {
110 }
112 } else {
114 }
116 #endif
117 return 0;
118 }
119
121 {
123
125 return -1;
126 }
127
129 case 1:
132 break;
133 case 2:
136 break;
137 default:
138 case 3:
143 else
145 break;
146 }
147
150 *bit_rate =
s->bit_rate;
151 return s->frame_size;
152 }