mirror of https://github.com/FFmpeg/FFmpeg.git
Originally committed as revision 7923 to svn://svn.ffmpeg.org/ffmpeg/trunkpull/126/head
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/*
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* AC3 decoder |
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* Copyright (c) 2001 Fabrice Bellard. |
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* |
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* This file is part of FFmpeg. |
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* |
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* FFmpeg 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 2.1 of the License, or (at your option) any later version. |
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* |
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* FFmpeg 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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* |
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* You should have received a copy of the GNU Lesser General Public |
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* License along with FFmpeg; if not, write to the Free Software |
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
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*/ |
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/**
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* @file ac3dec.c |
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* AC3 decoder. |
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*/ |
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//#define DEBUG
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#include "avcodec.h" |
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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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uint8_t *inbuf_ptr; |
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int frame_size; |
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int flags; |
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int channels; |
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ac3_state_t state; |
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} AC3DecodeState; |
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static int ac3_decode_init(AVCodecContext *avctx) |
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{ |
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AC3DecodeState *s = avctx->priv_data; |
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ac3_init (); |
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s->inbuf_ptr = s->inbuf; |
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s->frame_size = 0; |
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return 0; |
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} |
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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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{ |
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if (i > 0x43c07fff) |
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return 32767; |
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else if (i < 0x43bf8000) |
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return -32768; |
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else |
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return i - 0x43c00000; |
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} |
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static inline void float_to_int (float * _f, int16_t * s16, int nchannels) |
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{ |
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int i, j, c; |
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int32_t * f = (int32_t *) _f; // XXX assumes IEEE float format
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j = 0; |
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nchannels *= 256; |
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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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} |
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} |
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/**** end */ |
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#define HEADER_SIZE 7 |
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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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{ |
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AC3DecodeState *s = avctx->priv_data; |
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uint8_t *buf_ptr; |
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int flags, i, len; |
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int sample_rate, bit_rate; |
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short *out_samples = data; |
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float level; |
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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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}; |
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buf_ptr = buf; |
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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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if (len > buf_size) |
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len = buf_size; |
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memcpy(s->inbuf_ptr, buf_ptr, len); |
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buf_ptr += len; |
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s->inbuf_ptr += len; |
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buf_size -= 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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if (len == 0) { |
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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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s->inbuf_ptr--; |
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} else { |
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s->frame_size = len; |
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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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s->channels++; |
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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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av_log( avctx, AV_LOG_INFO, "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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} |
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avctx->bit_rate = bit_rate; |
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} |
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} |
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} else if (len < s->frame_size) { |
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len = s->frame_size - len; |
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if (len > buf_size) |
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len = buf_size; |
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memcpy(s->inbuf_ptr, buf_ptr, len); |
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buf_ptr += len; |
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s->inbuf_ptr += len; |
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buf_size -= len; |
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} else { |
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flags = s->flags; |
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if (avctx->channels == 1) |
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flags = AC3_MONO; |
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else if (avctx->channels == 2) |
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flags = AC3_STEREO; |
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else |
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flags |= AC3_ADJUST_LEVEL; |
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level = 1; |
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if (ac3_frame (&s->state, s->inbuf, &flags, &level, 384)) { |
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fail: |
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s->inbuf_ptr = s->inbuf; |
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s->frame_size = 0; |
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continue; |
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} |
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for (i = 0; i < 6; i++) { |
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if (ac3_block (&s->state)) |
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goto fail; |
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float_to_int (*samples, out_samples + i * 256 * avctx->channels, avctx->channels); |
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} |
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s->inbuf_ptr = s->inbuf; |
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s->frame_size = 0; |
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*data_size = 6 * avctx->channels * 256 * sizeof(int16_t); |
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break; |
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} |
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} |
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return buf_ptr - buf; |
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} |
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static int ac3_decode_end(AVCodecContext *s) |
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{ |
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return 0; |
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} |
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AVCodec ac3_decoder = { |
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"ac3", |
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CODEC_TYPE_AUDIO, |
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CODEC_ID_AC3, |
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sizeof(AC3DecodeState), |
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ac3_decode_init, |
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NULL, |
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ac3_decode_end, |
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ac3_decode_frame, |
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}; |
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