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/macros.h"
28
29#include "mpegaudio.h"
30#include "mpegaudiodata.h"
31#include "mpegaudiodecheader.h"
32
33
34int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
35{
36    int sample_rate, frame_size, mpeg25, padding;
37    int sample_rate_index, bitrate_index;
38    int ret;
39
40    ret = ff_mpa_check_header(header);
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(ff_mpa_freq_tab))
56        sample_rate_index = 0;
57    sample_rate = ff_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 = ff_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
120int 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:
130        *codec_id = AV_CODEC_ID_MP1;
131        *frame_size = 384;
132        break;
133    case 2:
134        *codec_id = AV_CODEC_ID_MP2;
135        *frame_size = 1152;
136        break;
137    default:
138    case 3:
139        if (*codec_id != AV_CODEC_ID_MP3ADU)
140            *codec_id = AV_CODEC_ID_MP3;
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}
153