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 Libav.
7  *
8  * Libav 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  * Libav 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 Libav; 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 
26 
27 typedef struct MpegAudioParseContext {
30  uint32_t header;
33 
34 #define MPA_HEADER_SIZE 4
35 
36 /* header + layer + bitrate + freq + lsf/mpeg25 */
37 #define SAME_HEADER_MASK \
38  (0xffe00000 | (3 << 17) | (3 << 10) | (3 << 19))
39 
41  AVCodecContext *avctx,
42  const uint8_t **poutbuf, int *poutbuf_size,
43  const uint8_t *buf, int buf_size)
44 {
46  ParseContext *pc = &s->pc;
47  uint32_t state= pc->state;
48  int i;
49  int next= END_NOT_FOUND;
50 
51  for(i=0; i<buf_size; ){
52  if(s->frame_size){
53  int inc= FFMIN(buf_size - i, s->frame_size);
54  i += inc;
55  s->frame_size -= inc;
56 
57  if(!s->frame_size){
58  next= i;
59  break;
60  }
61  }else{
62  while(i<buf_size){
63  int ret, sr, channels, bit_rate, frame_size;
64 
65  state= (state<<8) + buf[i++];
66 
67  ret = avpriv_mpa_decode_header(avctx, state, &sr, &channels, &frame_size, &bit_rate);
68  if (ret < 4) {
69  s->header_count= -2;
70  } else {
71  if((state&SAME_HEADER_MASK) != (s->header&SAME_HEADER_MASK) && s->header)
72  s->header_count= -3;
73  s->header= state;
74  s->header_count++;
75  s->frame_size = ret-4;
76 
77  if(s->header_count > 1){
78  avctx->sample_rate= sr;
79  avctx->channels = channels;
80  avctx->frame_size = frame_size;
81  avctx->bit_rate = bit_rate;
82  }
83  break;
84  }
85  }
86  }
87  }
88 
89  pc->state= state;
90  if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
91  *poutbuf = NULL;
92  *poutbuf_size = 0;
93  return buf_size;
94  }
95 
96  *poutbuf = buf;
97  *poutbuf_size = buf_size;
98  return next;
99 }
100 
101 
104  .priv_data_size = sizeof(MpegAudioParseContext),
105  .parser_parse = mpegaudio_parse,
106  .parser_close = ff_parse_close,
107 };