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1 | /* |
2 | * MPEG Audio decoder | |
3 | * Copyright (c) 2001 Gerard Lantau. | |
4 | * | |
5 | * This program is free software; you can redistribute it and/or modify | |
6 | * it under the terms of the GNU General Public License as published by | |
7 | * the Free Software Foundation; either version 2 of the License, or | |
8 | * (at your option) any later version. | |
9 | * | |
10 | * This program is distributed in the hope that it will be useful, | |
11 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | * GNU General Public License for more details. | |
14 | * | |
15 | * You should have received a copy of the GNU General Public License | |
16 | * along with this program; if not, write to the Free Software | |
17 | * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |
18 | */ | |
19 | #include <stdlib.h> | |
20 | #include <stdio.h> | |
21 | #include <string.h> | |
22 | #include "avcodec.h" | |
23 | #include "mpglib/mpg123.h" | |
24 | ||
25 | /* | |
26 | * TODO: | |
27 | * - add free format | |
28 | * - do not rely anymore on mpglib (first step: implement dct64 and decoding filter) | |
29 | */ | |
30 | ||
31 | #define HEADER_SIZE 4 | |
32 | #define BACKSTEP_SIZE 512 | |
33 | ||
34 | typedef struct MPADecodeContext { | |
35 | struct mpstr mpstr; | |
36 | UINT8 inbuf1[2][MAXFRAMESIZE + BACKSTEP_SIZE]; /* input buffer */ | |
37 | int inbuf_index; | |
38 | UINT8 *inbuf_ptr, *inbuf; | |
39 | int frame_size; | |
40 | int error_protection; | |
41 | int layer; | |
42 | int sample_rate; | |
43 | int bit_rate; | |
44 | int old_frame_size; | |
45 | GetBitContext gb; | |
46 | } MPADecodeContext; | |
47 | ||
48 | /* XXX: suppress that mess */ | |
49 | struct mpstr *gmp; | |
50 | GetBitContext *gmp_gb; | |
51 | static MPADecodeContext *gmp_s; | |
52 | ||
53 | /* XXX: merge constants with encoder */ | |
54 | static const unsigned short mp_bitrate_tab[2][3][15] = { | |
55 | { {0, 32, 64, 96, 128, 160, 192, 224, 256, 288, 320, 352, 384, 416, 448 }, | |
56 | {0, 32, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320, 384 }, | |
57 | {0, 32, 40, 48, 56, 64, 80, 96, 112, 128, 160, 192, 224, 256, 320 } }, | |
58 | { {0, 32, 48, 56, 64, 80, 96, 112, 128, 144, 160, 176, 192, 224, 256}, | |
59 | {0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160}, | |
60 | {0, 8, 16, 24, 32, 40, 48, 56, 64, 80, 96, 112, 128, 144, 160} | |
61 | } | |
62 | }; | |
63 | ||
64 | static unsigned short mp_freq_tab[3] = { 44100, 48000, 32000 }; | |
65 | ||
66 | static int decode_init(AVCodecContext * avctx) | |
67 | { | |
68 | MPADecodeContext *s = avctx->priv_data; | |
69 | struct mpstr *mp = &s->mpstr; | |
70 | static int init; | |
71 | ||
72 | mp->fr.single = -1; | |
73 | mp->synth_bo = 1; | |
74 | ||
75 | if(!init) { | |
76 | init = 1; | |
77 | make_decode_tables(32767); | |
78 | init_layer2(); | |
79 | init_layer3(SBLIMIT); | |
80 | } | |
81 | ||
82 | s->inbuf_index = 0; | |
83 | s->inbuf = &s->inbuf1[s->inbuf_index][BACKSTEP_SIZE]; | |
84 | s->inbuf_ptr = s->inbuf; | |
85 | ||
86 | return 0; | |
87 | } | |
88 | ||
89 | /* fast header check for resync */ | |
90 | static int check_header(UINT32 header) | |
91 | { | |
92 | /* header */ | |
93 | if ((header & 0xffe00000) != 0xffe00000) | |
94 | return -1; | |
95 | /* layer check */ | |
96 | if (((header >> 17) & 3) == 0) | |
97 | return -1; | |
98 | /* bit rate : currently no free format supported */ | |
99 | if (((header >> 12) & 0xf) == 0xf || | |
100 | ((header >> 12) & 0xf) == 0x0) | |
101 | return -1; | |
102 | /* frequency */ | |
103 | if (((header >> 10) & 3) == 3) | |
104 | return -1; | |
105 | return 0; | |
106 | } | |
107 | ||
108 | /* header decoding. MUST check the header before because no | |
109 | consistency check is done there */ | |
110 | static void decode_header(MPADecodeContext *s, UINT32 header) | |
111 | { | |
112 | struct frame *fr = &s->mpstr.fr; | |
113 | int sample_rate, frame_size; | |
114 | ||
115 | if (header & (1<<20)) { | |
116 | fr->lsf = (header & (1<<19)) ? 0 : 1; | |
117 | fr->mpeg25 = 0; | |
118 | } else { | |
119 | fr->lsf = 1; | |
120 | fr->mpeg25 = 1; | |
121 | } | |
122 | ||
123 | s->layer = 4 - ((header >> 17) & 3); | |
124 | /* extract frequency */ | |
125 | fr->sampling_frequency = ((header >> 10) & 3); | |
126 | sample_rate = mp_freq_tab[fr->sampling_frequency] >> (fr->lsf + fr->mpeg25); | |
127 | fr->sampling_frequency += 3 * (fr->lsf + fr->mpeg25); | |
128 | ||
129 | s->error_protection = ((header>>16) & 1) ^ 1; | |
130 | ||
131 | fr->bitrate_index = ((header>>12)&0xf); | |
132 | fr->padding = ((header>>9)&0x1); | |
133 | fr->extension = ((header>>8)&0x1); | |
134 | fr->mode = ((header>>6)&0x3); | |
135 | fr->mode_ext = ((header>>4)&0x3); | |
136 | fr->copyright = ((header>>3)&0x1); | |
137 | fr->original = ((header>>2)&0x1); | |
138 | fr->emphasis = header & 0x3; | |
139 | ||
140 | fr->stereo = (fr->mode == MPG_MD_MONO) ? 1 : 2; | |
141 | ||
142 | ||
143 | frame_size = mp_bitrate_tab[fr->lsf][s->layer - 1][fr->bitrate_index]; | |
144 | s->bit_rate = frame_size * 1000; | |
145 | switch(s->layer) { | |
146 | case 1: | |
147 | frame_size = (frame_size * 12000) / sample_rate; | |
148 | frame_size = ((frame_size + fr->padding) << 2); | |
149 | break; | |
150 | case 2: | |
151 | frame_size = (frame_size * 144000) / sample_rate; | |
152 | frame_size += fr->padding; | |
153 | break; | |
154 | case 3: | |
155 | frame_size = (frame_size * 144000) / (sample_rate << fr->lsf); | |
156 | frame_size += fr->padding; | |
157 | break; | |
158 | } | |
159 | s->frame_size = frame_size; | |
160 | s->sample_rate = sample_rate; | |
161 | ||
162 | #if 0 | |
163 | printf("layer%d, %d Hz, %d kbits/s, %s\n", | |
164 | s->layer, s->sample_rate, s->bit_rate, fr->stereo ? "stereo" : "mono"); | |
165 | #endif | |
166 | } | |
167 | ||
168 | static int mp_decode_frame(MPADecodeContext *s, | |
169 | short *samples) | |
170 | { | |
171 | int nb_bytes; | |
172 | ||
173 | init_get_bits(&s->gb, s->inbuf + HEADER_SIZE, s->inbuf_ptr - s->inbuf - HEADER_SIZE); | |
174 | ||
175 | /* skip error protection field */ | |
176 | if (s->error_protection) | |
177 | get_bits(&s->gb, 16); | |
178 | ||
179 | /* XXX: horrible: global! */ | |
180 | gmp = &s->mpstr; | |
181 | gmp_s = s; | |
182 | gmp_gb = &s->gb; | |
183 | ||
184 | nb_bytes = 0; | |
185 | switch(s->layer) { | |
186 | case 1: | |
187 | do_layer1(&s->mpstr.fr,(unsigned char *)samples, &nb_bytes); | |
188 | break; | |
189 | case 2: | |
190 | do_layer2(&s->mpstr.fr,(unsigned char *)samples, &nb_bytes); | |
191 | break; | |
192 | case 3: | |
193 | do_layer3(&s->mpstr.fr,(unsigned char *)samples, &nb_bytes); | |
194 | s->inbuf_index ^= 1; | |
195 | s->inbuf = &s->inbuf1[s->inbuf_index][BACKSTEP_SIZE]; | |
196 | s->old_frame_size = s->frame_size; | |
197 | break; | |
198 | default: | |
199 | break; | |
200 | } | |
201 | return nb_bytes; | |
202 | } | |
203 | ||
204 | /* | |
205 | * seek back in the stream for backstep bytes (at most 511 bytes, and | |
206 | * at most in last frame). Note that this is slightly incorrect (data | |
207 | * can span more than one block!) | |
208 | */ | |
209 | int set_pointer(long backstep) | |
210 | { | |
211 | UINT8 *ptr; | |
212 | ||
213 | /* compute current position in stream */ | |
214 | ptr = gmp_gb->buf_ptr - (gmp_gb->bit_cnt >> 3); | |
215 | /* copy old data before current one */ | |
216 | ptr -= backstep; | |
217 | memcpy(ptr, gmp_s->inbuf1[gmp_s->inbuf_index ^ 1] + | |
218 | BACKSTEP_SIZE + gmp_s->old_frame_size - backstep, backstep); | |
219 | /* init get bits again */ | |
220 | init_get_bits(gmp_gb, ptr, gmp_s->frame_size + backstep); | |
221 | ||
222 | return 0; | |
223 | } | |
224 | ||
225 | static int decode_frame(AVCodecContext * avctx, | |
226 | void *data, int *data_size, | |
227 | UINT8 * buf, int buf_size) | |
228 | { | |
229 | MPADecodeContext *s = avctx->priv_data; | |
230 | UINT32 header; | |
231 | UINT8 *buf_ptr; | |
232 | int len, out_size; | |
233 | short *out_samples = data; | |
234 | ||
235 | *data_size = 0; | |
236 | buf_ptr = buf; | |
237 | while (buf_size > 0) { | |
238 | len = s->inbuf_ptr - s->inbuf; | |
239 | if (s->frame_size == 0) { | |
240 | /* no header seen : find one. We need at least 7 bytes to parse it */ | |
241 | len = HEADER_SIZE - len; | |
242 | if (len > buf_size) | |
243 | len = buf_size; | |
244 | memcpy(s->inbuf_ptr, buf_ptr, len); | |
245 | buf_ptr += len; | |
246 | s->inbuf_ptr += len; | |
247 | buf_size -= len; | |
248 | if ((s->inbuf_ptr - s->inbuf) == HEADER_SIZE) { | |
249 | header = (s->inbuf[0] << 24) | (s->inbuf[1] << 16) | | |
250 | (s->inbuf[2] << 8) | s->inbuf[3]; | |
251 | if (check_header(header) < 0) { | |
252 | /* no sync found : move by one byte (inefficient, but simple!) */ | |
253 | memcpy(s->inbuf, s->inbuf + 1, HEADER_SIZE - 1); | |
254 | s->inbuf_ptr--; | |
255 | } else { | |
256 | decode_header(s, header); | |
257 | /* update codec info */ | |
258 | avctx->sample_rate = s->sample_rate; | |
259 | avctx->channels = s->mpstr.fr.stereo ? 2 : 1; | |
260 | avctx->bit_rate = s->bit_rate; | |
261 | } | |
262 | } | |
263 | } else if (len < s->frame_size) { | |
264 | len = s->frame_size - len; | |
265 | if (len > buf_size) | |
266 | len = buf_size; | |
267 | ||
268 | memcpy(s->inbuf_ptr, buf_ptr, len); | |
269 | buf_ptr += len; | |
270 | s->inbuf_ptr += len; | |
271 | buf_size -= len; | |
272 | } else { | |
273 | out_size = mp_decode_frame(s, out_samples); | |
274 | s->inbuf_ptr = s->inbuf; | |
275 | s->frame_size = 0; | |
276 | *data_size = out_size; | |
277 | break; | |
278 | } | |
279 | } | |
280 | return buf_ptr - buf; | |
281 | } | |
282 | ||
283 | AVCodec mp3_decoder = | |
284 | { | |
285 | "mpegaudio", | |
286 | CODEC_TYPE_AUDIO, | |
287 | CODEC_ID_MP2, | |
288 | sizeof(MPADecodeContext), | |
289 | decode_init, | |
290 | NULL, | |
291 | NULL, | |
292 | decode_frame, | |
293 | }; |