Libav
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 #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 
59  if(!s->frame_size){
60  next= i;
61  break;
62  }
63  }else{
64  while(i<buf_size){
65  int ret, sr, channels, bit_rate, frame_size;
66 
67  state= (state<<8) + buf[i++];
68 
69  ret = avpriv_mpa_decode_header(avctx, state, &sr, &channels, &frame_size, &bit_rate);
70  if (ret < 4) {
71  if (i > 4)
72  s->header_count = -2;
73  } else {
74  if((state&SAME_HEADER_MASK) != (s->header&SAME_HEADER_MASK) && s->header)
75  s->header_count= -3;
76  s->header= state;
77  s->header_count++;
78  s->frame_size = ret-4;
79 
80  if (s->header_count > 0) {
81  avctx->sample_rate= sr;
82  avctx->channels = channels;
83  s1->duration = frame_size;
84  if (s->no_bitrate || !avctx->bit_rate) {
85  s->no_bitrate = 1;
86  avctx->bit_rate += (bit_rate - avctx->bit_rate) / s->header_count;
87  }
88  }
89  break;
90  }
91  }
92  }
93  }
94 
95  pc->state= state;
96  if (ff_combine_frame(pc, next, &buf, &buf_size) < 0) {
97  *poutbuf = NULL;
98  *poutbuf_size = 0;
99  return buf_size;
100  }
101 
102  *poutbuf = buf;
103  *poutbuf_size = buf_size;
104  return next;
105 }
106 
107 
110  .priv_data_size = sizeof(MpegAudioParseContext),
111  .parser_parse = mpegaudio_parse,
112  .parser_close = ff_parse_close,
113 };
#define SAME_HEADER_MASK
int codec_ids[5]
Definition: avcodec.h:3838
int duration
Duration of the current frame.
Definition: avcodec.h:3814
uint8_t
static int mpegaudio_parse(AVCodecParserContext *s1, AVCodecContext *avctx, const uint8_t **poutbuf, int *poutbuf_size, const uint8_t *buf, int buf_size)
int ff_combine_frame(ParseContext *pc, int next, const uint8_t **buf, int *buf_size)
Combine the (truncated) bitstream to a complete frame.
Definition: parser.c:217
preferred ID for decoding MPEG audio layer 1, 2 or 3
Definition: avcodec.h:379
int avpriv_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
void ff_parse_close(AVCodecParserContext *s)
Definition: parser.c:287
int bit_rate
the average bitrate
Definition: avcodec.h:1114
#define FFMIN(a, b)
Definition: common.h:57
NULL
Definition: eval.c:55
int sample_rate
samples per second
Definition: avcodec.h:1807
main external API structure.
Definition: avcodec.h:1050
uint32_t state
contains the last few bytes in MSB order
Definition: parser.h:33
AVCodecParser ff_mpegaudio_parser
#define END_NOT_FOUND
Definition: parser.h:40
static uint32_t state
Definition: trasher.c:27
MPEG Audio header decoder.
common internal and external API header
int channels
number of audio channels
Definition: avcodec.h:1808