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"
30 #include "mpegaudio.h"
31 #include "mpegaudiodata.h"
32 #include "mpegaudiodecheader.h"
35 int avpriv_mpegaudio_decode_header(MPADecodeHeader *s, uint32_t header)
37 int sample_rate, frame_size, mpeg25, padding;
38 int sample_rate_index, bitrate_index;
39 if (header & (1<<20)) {
40 s->lsf = (header & (1<<19)) ? 0 : 1;
47 s->layer = 4 - ((header >> 17) & 3);
48 /* extract frequency */
49 sample_rate_index = (header >> 10) & 3;
50 if (sample_rate_index >= FF_ARRAY_ELEMS(avpriv_mpa_freq_tab))
51 sample_rate_index = 0;
52 sample_rate = avpriv_mpa_freq_tab[sample_rate_index] >> (s->lsf + mpeg25);
53 sample_rate_index += 3 * (s->lsf + mpeg25);
54 s->sample_rate_index = sample_rate_index;
55 s->error_protection = ((header >> 16) & 1) ^ 1;
56 s->sample_rate = sample_rate;
58 bitrate_index = (header >> 12) & 0xf;
59 padding = (header >> 9) & 1;
60 //extension = (header >> 8) & 1;
61 s->mode = (header >> 6) & 3;
62 s->mode_ext = (header >> 4) & 3;
63 //copyright = (header >> 3) & 1;
64 //original = (header >> 2) & 1;
65 //emphasis = header & 3;
67 if (s->mode == MPA_MONO)
72 if (bitrate_index != 0) {
73 frame_size = avpriv_mpa_bitrate_tab[s->lsf][s->layer - 1][bitrate_index];
74 s->bit_rate = frame_size * 1000;
77 frame_size = (frame_size * 12000) / sample_rate;
78 frame_size = (frame_size + padding) * 4;
81 frame_size = (frame_size * 144000) / sample_rate;
82 frame_size += padding;
86 frame_size = (frame_size * 144000) / (sample_rate << s->lsf);
87 frame_size += padding;
90 s->frame_size = frame_size;
92 /* if no frame size computed, signal it */
97 av_dlog(NULL, "layer%d, %d Hz, %d kbits/s, ",
98 s->layer, s->sample_rate, s->bit_rate);
99 if (s->nb_channels == 2) {
101 if (s->mode_ext & MODE_EXT_MS_STEREO)
102 av_dlog(NULL, "ms-");
103 if (s->mode_ext & MODE_EXT_I_STEREO)
106 av_dlog(NULL, "stereo");
108 av_dlog(NULL, "mono");
115 int avpriv_mpa_decode_header2(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
117 MPADecodeHeader s1, *s = &s1;
119 if (ff_mpa_check_header(head) != 0)
122 if (avpriv_mpegaudio_decode_header(s, head) != 0) {
128 *codec_id = AV_CODEC_ID_MP1;
132 *codec_id = AV_CODEC_ID_MP2;
137 *codec_id = AV_CODEC_ID_MP3;
145 *sample_rate = s->sample_rate;
146 *channels = s->nb_channels;
147 *bit_rate = s->bit_rate;
148 return s->frame_size;
151 int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
153 return avpriv_mpa_decode_header2(head, sample_rate, channels, frame_size, bit_rate, &avctx->codec_id);