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mp3dec.c
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1 /*
2  * MP3 demuxer
3  * Copyright (c) 2003 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 #include "libavutil/avstring.h"
23 #include "libavutil/intreadwrite.h"
24 #include "libavutil/dict.h"
25 #include "libavutil/mathematics.h"
26 #include "avformat.h"
27 #include "internal.h"
28 #include "id3v2.h"
29 #include "id3v1.h"
31 
32 #define XING_FLAG_FRAMES 0x01
33 #define XING_FLAG_SIZE 0x02
34 #define XING_FLAG_TOC 0x04
35 
36 #define XING_TOC_COUNT 100
37 
38 typedef struct {
39  int64_t filesize;
40  int xing_toc;
41  int start_pad;
42  int end_pad;
43 } MP3Context;
44 
45 /* mp3 read */
46 
48 {
49  int max_frames, first_frames = 0;
50  int fsize, frames, sample_rate;
51  uint32_t header;
52  const uint8_t *buf, *buf0, *buf2, *end;
53  AVCodecContext avctx;
54 
55  buf0 = p->buf;
56  end = p->buf + p->buf_size - sizeof(uint32_t);
57  while(buf0 < end && !*buf0)
58  buf0++;
59 
60  max_frames = 0;
61  buf = buf0;
62 
63  for(; buf < end; buf= buf2+1) {
64  buf2 = buf;
65 
66  for(frames = 0; buf2 < end; frames++) {
67  header = AV_RB32(buf2);
68  fsize = avpriv_mpa_decode_header(&avctx, header, &sample_rate, &sample_rate, &sample_rate, &sample_rate);
69  if(fsize < 0)
70  break;
71  buf2 += fsize;
72  }
73  max_frames = FFMAX(max_frames, frames);
74  if(buf == buf0)
75  first_frames= frames;
76  }
77  // keep this in sync with ac3 probe, both need to avoid
78  // issues with MPEG-files!
79  if (first_frames>=4) return AVPROBE_SCORE_MAX/2+1;
80  else if(max_frames>200)return AVPROBE_SCORE_MAX/2;
81  else if(max_frames>=4) return AVPROBE_SCORE_MAX/4;
82  else if(ff_id3v2_match(buf0, ID3v2_DEFAULT_MAGIC) && 2*ff_id3v2_tag_len(buf0) >= p->buf_size)
83  return AVPROBE_SCORE_MAX/8;
84  else if(max_frames>=1) return 1;
85  else return 0;
86 //mpegps_mp3_unrecognized_format.mpg has max_frames=3
87 }
88 
89 static void read_xing_toc(AVFormatContext *s, int64_t filesize, int64_t duration)
90 {
91  int i;
92  MP3Context *mp3 = s->priv_data;
93 
94  if (!filesize &&
95  !(filesize = avio_size(s->pb))) {
96  av_log(s, AV_LOG_WARNING, "Cannot determine file size, skipping TOC table.\n");
97  return;
98  }
99 
100  for (i = 0; i < XING_TOC_COUNT; i++) {
101  uint8_t b = avio_r8(s->pb);
102 
104  av_rescale(b, filesize, 256),
105  av_rescale(i, duration, XING_TOC_COUNT),
106  0, 0, AVINDEX_KEYFRAME);
107  }
108  mp3->xing_toc = 1;
109 }
110 
111 /**
112  * Try to find Xing/Info/VBRI tags and compute duration from info therein
113  */
114 static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
115 {
116  MP3Context *mp3 = s->priv_data;
117  uint32_t v, spf;
118  unsigned frames = 0; /* Total number of frames in file */
119  unsigned size = 0; /* Total number of bytes in the stream */
120  const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
122  int vbrtag_size = 0;
123  int is_cbr;
124 
125  v = avio_rb32(s->pb);
126  if(ff_mpa_check_header(v) < 0)
127  return -1;
128 
129  if (avpriv_mpegaudio_decode_header(&c, v) == 0)
130  vbrtag_size = c.frame_size;
131  if(c.layer != 3)
132  return -1;
133 
134  spf = c.lsf ? 576 : 1152; /* Samples per frame, layer 3 */
135 
136  /* Check for Xing / Info tag */
137  avio_skip(s->pb, xing_offtbl[c.lsf == 1][c.nb_channels == 1]);
138  v = avio_rb32(s->pb);
139  is_cbr = v == MKBETAG('I', 'n', 'f', 'o');
140  if (v == MKBETAG('X', 'i', 'n', 'g') || is_cbr) {
141  v = avio_rb32(s->pb);
142  if(v & XING_FLAG_FRAMES)
143  frames = avio_rb32(s->pb);
144  if(v & XING_FLAG_SIZE)
145  size = avio_rb32(s->pb);
146  if (v & XING_FLAG_TOC && frames)
147  read_xing_toc(s, size, av_rescale_q(frames, (AVRational){spf, c.sample_rate},
148  st->time_base));
149  if(v & 8)
150  avio_skip(s->pb, 4);
151 
152  v = avio_rb32(s->pb);
153  if(v == MKBETAG('L', 'A', 'M', 'E') || v == MKBETAG('L', 'a', 'v', 'f')) {
154  avio_skip(s->pb, 21-4);
155  v= avio_rb24(s->pb);
156  mp3->start_pad = v>>12;
157  mp3-> end_pad = v&4095;
158  st->skip_samples = mp3->start_pad + 528 + 1;
159  av_log(s, AV_LOG_DEBUG, "pad %d %d\n", mp3->start_pad, mp3-> end_pad);
160  }
161  }
162 
163  /* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */
164  avio_seek(s->pb, base + 4 + 32, SEEK_SET);
165  v = avio_rb32(s->pb);
166  if(v == MKBETAG('V', 'B', 'R', 'I')) {
167  /* Check tag version */
168  if(avio_rb16(s->pb) == 1) {
169  /* skip delay and quality */
170  avio_skip(s->pb, 4);
171  size = avio_rb32(s->pb);
172  frames = avio_rb32(s->pb);
173  }
174  }
175 
176  if(!frames && !size)
177  return -1;
178 
179  /* Skip the vbr tag frame */
180  avio_seek(s->pb, base + vbrtag_size, SEEK_SET);
181 
182  if(frames)
183  st->duration = av_rescale_q(frames, (AVRational){spf, c.sample_rate},
184  st->time_base);
185  if (size && frames && !is_cbr)
186  st->codec->bit_rate = av_rescale(size, 8 * c.sample_rate, frames * (int64_t)spf);
187 
188  return 0;
189 }
190 
192 {
193  MP3Context *mp3 = s->priv_data;
194  AVStream *st;
195  int64_t off;
196 
197  st = avformat_new_stream(s, NULL);
198  if (!st)
199  return AVERROR(ENOMEM);
200 
204  st->start_time = 0;
205 
206  // lcm of all mp3 sample rates
207  avpriv_set_pts_info(st, 64, 1, 14112000);
208 
209  s->pb->maxsize = -1;
210  off = avio_tell(s->pb);
211 
213  ff_id3v1_read(s);
214 
215  if(s->pb->seekable)
216  mp3->filesize = avio_size(s->pb);
217 
218  if (mp3_parse_vbr_tags(s, st, off) < 0)
219  avio_seek(s->pb, off, SEEK_SET);
220 
221  /* the parameters will be extracted from the compressed bitstream */
222  return 0;
223 }
224 
225 #define MP3_PACKET_SIZE 1024
226 
228 {
229  MP3Context *mp3 = s->priv_data;
230  int ret, size;
231  int64_t pos;
232 
233  size= MP3_PACKET_SIZE;
234  pos = avio_tell(s->pb);
235  if(mp3->filesize > ID3v1_TAG_SIZE && pos < mp3->filesize)
236  size= FFMIN(size, mp3->filesize - pos);
237 
238  ret= av_get_packet(s->pb, pkt, size);
239  if (ret <= 0) {
240  if(ret<0)
241  return ret;
242  return AVERROR_EOF;
243  }
244 
245  pkt->flags &= ~AV_PKT_FLAG_CORRUPT;
246  pkt->stream_index = 0;
247 
248  if (ret >= ID3v1_TAG_SIZE &&
249  memcmp(&pkt->data[ret - ID3v1_TAG_SIZE], "TAG", 3) == 0)
250  ret -= ID3v1_TAG_SIZE;
251 
252  /* note: we need to modify the packet size here to handle the last
253  packet */
254  pkt->size = ret;
255  return ret;
256 }
257 
258 static int check(AVFormatContext *s, int64_t pos)
259 {
260  int64_t ret = avio_seek(s->pb, pos, SEEK_SET);
261  unsigned header;
262  MPADecodeHeader sd;
263  if (ret < 0)
264  return ret;
265  header = avio_rb32(s->pb);
266  if (ff_mpa_check_header(header) < 0)
267  return -1;
268  if (avpriv_mpegaudio_decode_header(&sd, header) == 1)
269  return -1;
270  return sd.frame_size;
271 }
272 
273 static int mp3_seek(AVFormatContext *s, int stream_index, int64_t timestamp,
274  int flags)
275 {
276  MP3Context *mp3 = s->priv_data;
277  AVIndexEntry *ie;
278  AVStream *st = s->streams[0];
279  int64_t ret = av_index_search_timestamp(st, timestamp, flags);
280  int i, j;
281 
282  if (!mp3->xing_toc) {
283  st->skip_samples = timestamp <= 0 ? mp3->start_pad + 528 + 1 : 0;
284 
285  return -1;
286  }
287 
288  if (ret < 0)
289  return ret;
290 
291  ie = &st->index_entries[ret];
292  ret = avio_seek(s->pb, ie->pos, SEEK_SET);
293  if (ret < 0)
294  return ret;
295 
296 #define MIN_VALID 3
297  for(i=0; i<4096; i++) {
298  int64_t pos = ie->pos + i;
299  for(j=0; j<MIN_VALID; j++) {
300  ret = check(s, pos);
301  if(ret < 0)
302  break;
303  pos += ret;
304  }
305  if(j==MIN_VALID)
306  break;
307  }
308  if(j!=MIN_VALID)
309  i=0;
310 
311  ret = avio_seek(s->pb, ie->pos + i, SEEK_SET);
312  if (ret < 0)
313  return ret;
314  ff_update_cur_dts(s, st, ie->timestamp);
315  st->skip_samples = ie->timestamp <= 0 ? mp3->start_pad + 528 + 1 : 0;
316  return 0;
317 }
318 
320  .name = "mp3",
321  .long_name = NULL_IF_CONFIG_SMALL("MP2/3 (MPEG audio layer 2/3)"),
322  .priv_data_size = sizeof(MP3Context),
326  .read_seek = mp3_seek,
328  .extensions = "mp2,mp3,m2a", /* XXX: use probe */
329 };