path: root/libavcodec/mpegaudiodecheader.c (plain)
blob: ae86b087f3ee21d15d1c42923d1523b9ddeaf5d6

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
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
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
156	#if LIBAVCODEC_VERSION_MAJOR < 58
157	int avpriv_mpa_decode_header2(uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate, enum AVCodecID *codec_id)
158	{
159	return ff_mpa_decode_header(head, sample_rate, channels, frame_size, bit_rate, codec_id);
160	}
161
162	int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
163	{
164	return ff_mpa_decode_header(head, sample_rate, channels, frame_size, bit_rate, &avctx->codec_id);
165	}
166	#endif
167