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mpegaudio_parser.c
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1 /*
2  * MPEG Audio parser
3  * Copyright (c) 2003 Fabrice Bellard
4  * Copyright (c) 2003 Michael Niedermayer
5  *
6  * This file is part of FFmpeg.
7  *
8  * FFmpeg is free software; you can redistribute it and/or
9  * modify it under the terms of the GNU Lesser General Public
10  * License as published by the Free Software Foundation; either
11  * version 2.1 of the License, or (at your option) any later version.
12  *
13  * FFmpeg is distributed in the hope that it will be useful,
14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16  * Lesser General Public License for more details.
17  *
18  * You should have received a copy of the GNU Lesser General Public
19  * License along with FFmpeg; if not, write to the Free Software
20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21  */
22 
23 #include "parser.h"
24 #include "mpegaudiodecheader.h"
25 #include "libavutil/common.h"
26 
27 
28 typedef struct MpegAudioParseContext {
31  uint32_t header;
35 
36 #define MPA_HEADER_SIZE 4
37 
38 /* header + layer + bitrate + freq + lsf/mpeg25 */
39 #define SAME_HEADER_MASK \
40  (0xffe00000 | (3 << 17) | (3 << 10) | (3 << 19))
41 
43  AVCodecContext *avctx,
44  const uint8_t **poutbuf, int *poutbuf_size,
45  const uint8_t *buf, int buf_size)
46 {
48  ParseContext *pc = &s->pc;
49  uint32_t state= pc->state;
50  int i;
51  int next= END_NOT_FOUND;
52 
53  for(i=0; i<buf_size; ){
54  if(s->frame_size){
55  int inc= FFMIN(buf_size - i, s->frame_size);
56  i += inc;
57  s->frame_size -= inc;
58  state = 0;
59 
60  if(!s->frame_size){
61  next= i;
62  break;
63  }
64  }else{
65  while(i<buf_size){
66  int ret, sr, channels, bit_rate, frame_size;
67  enum AVCodecID codec_id;
68 
69  state= (state<<8) + buf[i++];
70 
71  ret = avpriv_mpa_decode_header2(state, &sr, &channels, &frame_size, &bit_rate, &codec_id);
72  if (ret < 4) {
73  if (i > 4)
74  s->header_count = -2;
75  } else {
76  int header_threshold = avctx->codec_id != AV_CODEC_ID_NONE && avctx->codec_id != codec_id;
77  if((state&SAME_HEADER_MASK) != (s->header&SAME_HEADER_MASK) && s->header)
78  s->header_count= -3;
79  s->header= state;
80  s->header_count++;
81  s->frame_size = ret-4;
82 
83  if (s->header_count > header_threshold) {
84  avctx->sample_rate= sr;
85  avctx->channels = channels;
86  s1->duration = frame_size;
87  avctx->codec_id = codec_id;
88  if (s->no_bitrate || !avctx->bit_rate) {
89  s->no_bitrate = 1;
90  avctx->bit_rate += (bit_rate - avctx->bit_rate) / (s->header_count - header_threshold);
91  }
92  }
93  break;
94  }
95  }
96  }
97  }
98 
99  pc->state= state;
100  if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
101  *poutbuf = NULL;
102  *poutbuf_size = 0;
103  return buf_size;
104  }
105 
106  *poutbuf = buf;
107  *poutbuf_size = buf_size;
108  return next;
109 }
110 
111 
114  .priv_data_size = sizeof(MpegAudioParseContext),
115  .parser_parse = mpegaudio_parse,
116  .parser_close = ff_parse_close,
117 };