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* Copyright (c) 2001 Fabrice Bellard.
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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#include "libac3/ac3.h"
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/* currently, I use libac3 which is Copyright (C) Aaron Holtzman and
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released under the GPL license. I may reimplement it someday... */
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typedef struct AC3DecodeState {
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uint8_t inbuf[4096]; /* input buffer */
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static int ac3_decode_init(AVCodecContext *avctx)
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AC3DecodeState *s = avctx->priv_data;
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s->inbuf_ptr = s->inbuf;
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stream_samples_t samples;
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/**** the following two functions comes from ac3dec */
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static inline int blah (int32_t i)
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else if (i < 0x43bf8000)
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return i - 0x43c00000;
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static inline void float_to_int (float * _f, int16_t * s16, int nchannels)
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int32_t * f = (int32_t *) _f; // XXX assumes IEEE float format
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for (i = 0; i < 256; i++) {
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for (c = 0; c < nchannels; c += 256)
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s16[j++] = blah (f[i + c]);
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static int ac3_decode_frame(AVCodecContext *avctx,
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void *data, int *data_size,
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uint8_t *buf, int buf_size)
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AC3DecodeState *s = avctx->priv_data;
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int sample_rate, bit_rate;
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short *out_samples = data;
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static const int ac3_channels[8] = {
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2, 1, 2, 3, 3, 4, 4, 5
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while (buf_size > 0) {
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len = s->inbuf_ptr - s->inbuf;
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if (s->frame_size == 0) {
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/* no header seen : find one. We need at least 7 bytes to parse it */
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len = HEADER_SIZE - len;
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memcpy(s->inbuf_ptr, buf_ptr, len);
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if ((s->inbuf_ptr - s->inbuf) == HEADER_SIZE) {
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len = ac3_syncinfo (s->inbuf, &s->flags, &sample_rate, &bit_rate);
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/* no sync found : move by one byte (inefficient, but simple!) */
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memcpy(s->inbuf, s->inbuf + 1, HEADER_SIZE - 1);
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/* update codec info */
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avctx->sample_rate = sample_rate;
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s->channels = ac3_channels[s->flags & 7];
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if (s->flags & AC3_LFE)
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if (avctx->channels == 0)
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/* No specific number of channel requested */
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avctx->channels = s->channels;
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else if (s->channels < avctx->channels) {
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fprintf(stderr, "ac3dec: AC3 Source channels are less than specified: output to %d channels.. (frmsize: %d)\n", s->channels, len);
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avctx->channels = s->channels;
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avctx->bit_rate = bit_rate;
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} else if (len < s->frame_size) {
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len = s->frame_size - len;
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memcpy(s->inbuf_ptr, buf_ptr, len);
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if (avctx->channels == 1)
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else if (avctx->channels == 2)
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flags |= AC3_ADJUST_LEVEL;
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if (ac3_frame (&s->state, s->inbuf, &flags, &level, 384)) {
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s->inbuf_ptr = s->inbuf;
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for (i = 0; i < 6; i++) {
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if (ac3_block (&s->state))
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float_to_int (*samples, out_samples + i * 256 * avctx->channels, avctx->channels);
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s->inbuf_ptr = s->inbuf;
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*data_size = 6 * avctx->channels * 256 * sizeof(int16_t);
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return buf_ptr - buf;
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static int ac3_decode_end(AVCodecContext *s)
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AVCodec ac3_decoder = {
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sizeof(AC3DecodeState),