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/*
* AC3 decoder
* Copyright (c) 2001 Gerard Lantau.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#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 inbuf[4096]; /* input buffer */
UINT8 *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 * 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 *buf, int buf_size)
{
AC3DecodeState *s = avctx->priv_data;
UINT8 *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
};
*data_size = 0;
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) {
fprintf(stderr, "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);
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,
};
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