2 * MPEG Audio header decoder
3 * Copyright (c) 2001, 2002 Fabrice Bellard
5 * This file is part of FFmpeg.
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.
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.
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
24 * MPEG Audio header decoder.
27 #include "libavutil/common.h"
31 #include "mpegaudio.h"
32 #include "mpegaudiodata.h"
33 #include "mpegaudiodecheader.h"
36 int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
38 int sample_rate, frame_size, mpeg25, padding;
39 int sample_rate_index, bitrate_index;
40 if (header & (1<<20)) {
41 s->lsf = (header & (1<<19)) ? 0 : 1;
48 s->layer = 4 - ((header >> 17) & 3);
49 /* extract frequency */
50 sample_rate_index = (header >> 10) & 3;
51 if (sample_rate_index >= FF_ARRAY_ELEMS(avpriv_mpa_freq_tab))
52 sample_rate_index = 0;
53 sample_rate = avpriv_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25);
54 sample_rate_index += 3 * (s->lsf + mpeg25);
55 s->sample_rate_index = sample_rate_index;
56 s->error_protection = ((header >> 16) & 1) ^ 1;
57 s->sample_rate = sample_rate;
59 bitrate_index = (header >> 12) & 0xf;
60 padding = (header >> 9) & 1;
61 //extension = (header >> 8) & 1;
62 s->mode = (header >> 6) & 3;
63 s->mode_ext = (header >> 4) & 3;
64 //copyright = (header >> 3) & 1;
65 //original = (header >> 2) & 1;
66 //emphasis = header & 3;
68 if (s->mode == MPA_MONO)
73 if (bitrate_index != 0) {
74 frame_size = avpriv_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index];
75 s->bit_rate = frame_size * 1000;
78 frame_size = (frame_size * 12000) / sample_rate;
79 frame_size = (frame_size + padding) * 4;
82 frame_size = (frame_size * 144000) / sample_rate;
83 frame_size += padding;
87 frame_size = (frame_size * 144000) / (sample_rate << s->lsf);
88 frame_size += padding;
91 s->frame_size = frame_size;
93 /* if no frame size computed, signal it */
98 ff_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ",
99 s->layer, s->sample_rate, s->bit_rate);
100 if (s->nb_channels == 2) {
102 if (s->mode_ext & MODE_EXT_MS_STEREO)
103 ff_dlog(NULL, "ms-");
104 if (s->mode_ext & MODE_EXT_I_STEREO)
107 ff_dlog(NULL, "stereo");
109 ff_dlog(NULL, "mono");
116 int avpriv_mpa_decode_header2(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
118 MPADecodeHeader s1, *s = &s1;
120 if (ff_mpa_check_header(head) != 0)
123 if (avpriv_mpegaudio_decode_header(s, head) != 0) {
129 *codec_id = AV_CODEC_ID_MP1;
133 *codec_id = AV_CODEC_ID_MP2;
138 if (*codec_id != AV_CODEC_ID_MP3ADU)
139 *codec_id = AV_CODEC_ID_MP3;
147 *sample_rate = s->sample_rate;
148 *channels = s->nb_channels;
149 *bit_rate = s->bit_rate;
150 return s->frame_size;
153 int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
155 return avpriv_mpa_decode_header2(head, sample_rate, channels, frame_size, bit_rate, &avctx->codec_id);