mp3dec.c
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1 /*
2  * MP3 demuxer
3  * Copyright (c) 2003 Fabrice Bellard
4  *
5  * This file is part of Libav.
6  *
7  * Libav 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  * Libav 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 Libav; 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 /* mp3 read */
33 
35 {
36  int max_frames, first_frames = 0;
37  int fsize, frames, sample_rate;
38  uint32_t header;
39  uint8_t *buf, *buf0, *buf2, *end;
40  AVCodecContext avctx;
41 
42  buf0 = p->buf;
43  end = p->buf + p->buf_size - sizeof(uint32_t);
44  while(buf0 < end && !*buf0)
45  buf0++;
46 
47  max_frames = 0;
48  buf = buf0;
49 
50  for(; buf < end; buf= buf2+1) {
51  buf2 = buf;
52 
53  for(frames = 0; buf2 < end; frames++) {
54  header = AV_RB32(buf2);
55  fsize = avpriv_mpa_decode_header(&avctx, header, &sample_rate, &sample_rate, &sample_rate, &sample_rate);
56  if(fsize < 0)
57  break;
58  buf2 += fsize;
59  }
60  max_frames = FFMAX(max_frames, frames);
61  if(buf == buf0)
62  first_frames= frames;
63  }
64  // keep this in sync with ac3 probe, both need to avoid
65  // issues with MPEG-files!
66  if (first_frames>=4) return AVPROBE_SCORE_MAX/2+1;
67  else if(max_frames>500)return AVPROBE_SCORE_MAX/2;
68  else if(max_frames>=4) return AVPROBE_SCORE_MAX/4;
69  else if(max_frames>=1) return 1;
70  else return 0;
71 //mpegps_mp3_unrecognized_format.mpg has max_frames=3
72 }
73 
77 static int mp3_parse_vbr_tags(AVFormatContext *s, AVStream *st, int64_t base)
78 {
79  uint32_t v, spf;
80  unsigned frames = 0; /* Total number of frames in file */
81  unsigned size = 0; /* Total number of bytes in the stream */
82  const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
84  int vbrtag_size = 0;
85 
86  v = avio_rb32(s->pb);
87  if(ff_mpa_check_header(v) < 0)
88  return -1;
89 
90  if (avpriv_mpegaudio_decode_header(&c, v) == 0)
91  vbrtag_size = c.frame_size;
92  if(c.layer != 3)
93  return -1;
94 
95  /* Check for Xing / Info tag */
96  avio_skip(s->pb, xing_offtbl[c.lsf == 1][c.nb_channels == 1]);
97  v = avio_rb32(s->pb);
98  if(v == MKBETAG('X', 'i', 'n', 'g') || v == MKBETAG('I', 'n', 'f', 'o')) {
99  v = avio_rb32(s->pb);
100  if(v & 0x1)
101  frames = avio_rb32(s->pb);
102  if(v & 0x2)
103  size = avio_rb32(s->pb);
104  }
105 
106  /* Check for VBRI tag (always 32 bytes after end of mpegaudio header) */
107  avio_seek(s->pb, base + 4 + 32, SEEK_SET);
108  v = avio_rb32(s->pb);
109  if(v == MKBETAG('V', 'B', 'R', 'I')) {
110  /* Check tag version */
111  if(avio_rb16(s->pb) == 1) {
112  /* skip delay and quality */
113  avio_skip(s->pb, 4);
114  frames = avio_rb32(s->pb);
115  size = avio_rb32(s->pb);
116  }
117  }
118 
119  if(!frames && !size)
120  return -1;
121 
122  /* Skip the vbr tag frame */
123  avio_seek(s->pb, base + vbrtag_size, SEEK_SET);
124 
125  spf = c.lsf ? 576 : 1152; /* Samples per frame, layer 3 */
126  if(frames)
127  st->duration = av_rescale_q(frames, (AVRational){spf, c.sample_rate},
128  st->time_base);
129  if(size && frames)
130  st->codec->bit_rate = av_rescale(size, 8 * c.sample_rate, frames * (int64_t)spf);
131 
132  return 0;
133 }
134 
136  AVFormatParameters *ap)
137 {
138  AVStream *st;
139  int64_t off;
140 
141  st = avformat_new_stream(s, NULL);
142  if (!st)
143  return AVERROR(ENOMEM);
144 
146  st->codec->codec_id = CODEC_ID_MP3;
148  st->start_time = 0;
149 
150  // lcm of all mp3 sample rates
151  avpriv_set_pts_info(st, 64, 1, 14112000);
152 
153  off = avio_tell(s->pb);
154 
156  ff_id3v1_read(s);
157 
158  if (mp3_parse_vbr_tags(s, st, off) < 0)
159  avio_seek(s->pb, off, SEEK_SET);
160 
161  /* the parameters will be extracted from the compressed bitstream */
162  return 0;
163 }
164 
165 #define MP3_PACKET_SIZE 1024
166 
168 {
169  int ret, size;
170  // AVStream *st = s->streams[0];
171 
172  size= MP3_PACKET_SIZE;
173 
174  ret= av_get_packet(s->pb, pkt, size);
175 
176  pkt->stream_index = 0;
177  if (ret <= 0) {
178  return AVERROR(EIO);
179  }
180 
181  if (ret > ID3v1_TAG_SIZE &&
182  memcmp(&pkt->data[ret - ID3v1_TAG_SIZE], "TAG", 3) == 0)
183  ret -= ID3v1_TAG_SIZE;
184 
185  /* note: we need to modify the packet size here to handle the last
186  packet */
187  pkt->size = ret;
188  return ret;
189 }
190 
192  .name = "mp3",
193  .long_name = NULL_IF_CONFIG_SMALL("MPEG audio layer 2/3"),
194  .read_probe = mp3_read_probe,
195  .read_header = mp3_read_header,
196  .read_packet = mp3_read_packet,
197  .flags= AVFMT_GENERIC_INDEX,
198  .extensions = "mp2,mp3,m2a", /* XXX: use probe */
199 };