1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
|
/*
* AC3 decoder
* Copyright (c) 2001 Fabrice Bellard.
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/**
* @file ac3dec.c
* AC3 decoder.
*/
//#define DEBUG
#include "avcodec.h"
#include "libac3/ac3.h"
/* currently, I use libac3 which is Copyright (C) Aaron Holtzman and
released under the GPL license. I may reimplement it someday... */
typedef struct AC3DecodeState {
uint8_t inbuf[4096]; /* input buffer */
uint8_t *inbuf_ptr;
int frame_size;
int flags;
int channels;
ac3_state_t state;
} AC3DecodeState;
static int ac3_decode_init(AVCodecContext *avctx)
{
AC3DecodeState *s = avctx->priv_data;
ac3_init ();
s->inbuf_ptr = s->inbuf;
s->frame_size = 0;
return 0;
}
stream_samples_t samples;
/**** the following two functions comes from ac3dec */
static inline int blah (int32_t i)
{
if (i > 0x43c07fff)
return 32767;
else if (i < 0x43bf8000)
return -32768;
else
return i - 0x43c00000;
}
static inline void float_to_int (float * _f, int16_t * s16, int nchannels)
{
int i, j, c;
int32_t * f = (int32_t *) _f; // XXX assumes IEEE float format
j = 0;
nchannels *= 256;
for (i = 0; i < 256; i++) {
for (c = 0; c < nchannels; c += 256)
s16[j++] = blah (f[i + c]);
}
}
/**** end */
#define HEADER_SIZE 7
static int ac3_decode_frame(AVCodecContext *avctx,
void *data, int *data_size,
uint8_t *buf, int buf_size)
{
AC3DecodeState *s = avctx->priv_data;
uint8_t *buf_ptr;
int flags, i, len;
int sample_rate, bit_rate;
short *out_samples = data;
float level;
static const int ac3_channels[8] = {
2, 1, 2, 3, 3, 4, 4, 5
};
buf_ptr = buf;
while (buf_size > 0) {
len = s->inbuf_ptr - s->inbuf;
if (s->frame_size == 0) {
/* no header seen : find one. We need at least 7 bytes to parse it */
len = HEADER_SIZE - len;
if (len > buf_size)
len = buf_size;
memcpy(s->inbuf_ptr, buf_ptr, len);
buf_ptr += len;
s->inbuf_ptr += len;
buf_size -= len;
if ((s->inbuf_ptr - s->inbuf) == HEADER_SIZE) {
len = ac3_syncinfo (s->inbuf, &s->flags, &sample_rate, &bit_rate);
if (len == 0) {
/* no sync found : move by one byte (inefficient, but simple!) */
memcpy(s->inbuf, s->inbuf + 1, HEADER_SIZE - 1);
s->inbuf_ptr--;
} else {
s->frame_size = len;
/* update codec info */
avctx->sample_rate = sample_rate;
s->channels = ac3_channels[s->flags & 7];
if (s->flags & AC3_LFE)
s->channels++;
if (avctx->channels == 0)
/* No specific number of channel requested */
avctx->channels = s->channels;
else if (s->channels < avctx->channels) {
av_log( avctx, AV_LOG_INFO, "ac3dec: AC3 Source channels are less than specified: output to %d channels.. (frmsize: %d)\n", s->channels, len);
avctx->channels = s->channels;
}
avctx->bit_rate = bit_rate;
}
}
} else if (len < s->frame_size) {
len = s->frame_size - len;
if (len > buf_size)
len = buf_size;
memcpy(s->inbuf_ptr, buf_ptr, len);
buf_ptr += len;
s->inbuf_ptr += len;
buf_size -= len;
} else {
flags = s->flags;
if (avctx->channels == 1)
flags = AC3_MONO;
else if (avctx->channels == 2)
flags = AC3_STEREO;
else
flags |= AC3_ADJUST_LEVEL;
level = 1;
if (ac3_frame (&s->state, s->inbuf, &flags, &level, 384)) {
fail:
s->inbuf_ptr = s->inbuf;
s->frame_size = 0;
continue;
}
for (i = 0; i < 6; i++) {
if (ac3_block (&s->state))
goto fail;
float_to_int (*samples, out_samples + i * 256 * avctx->channels, avctx->channels);
}
s->inbuf_ptr = s->inbuf;
s->frame_size = 0;
*data_size = 6 * avctx->channels * 256 * sizeof(int16_t);
break;
}
}
return buf_ptr - buf;
}
static int ac3_decode_end(AVCodecContext *s)
{
return 0;
}
AVCodec ac3_decoder = {
"ac3",
CODEC_TYPE_AUDIO,
CODEC_ID_AC3,
sizeof(AC3DecodeState),
ac3_decode_init,
NULL,
ac3_decode_end,
ac3_decode_frame,
};
|
