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/*
* Copyright (c) 2011 Justin Ruggles
*
* This file is part of Libav.
*
* Libav 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.
*
* Libav 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 Libav; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include "libavutil/intreadwrite.h"
#include "libavutil/mathematics.h"
#include "adx.h"
void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
{
double a, b, c;
a = M_SQRT2 - cos(2.0 * M_PI * cutoff / sample_rate);
b = M_SQRT2 - 1.0;
c = (a - sqrt((a + b) * (a - b))) / b;
coeff[0] = lrintf(c * 2.0 * (1 << bits));
coeff[1] = lrintf(-(c * c) * (1 << bits));
}
int avpriv_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf,
int bufsize, int *header_size, int *coeff)
{
int offset, cutoff;
if (bufsize < 24)
return AVERROR_INVALIDDATA;
if (AV_RB16(buf) != 0x8000)
return AVERROR_INVALIDDATA;
offset = AV_RB16(buf + 2) + 4;
/* if copyright string is within the provided data, validate it */
if (bufsize >= offset && memcmp(buf + offset - 6, "(c)CRI", 6))
return AVERROR_INVALIDDATA;
/* check for encoding=3 block_size=18, sample_size=4 */
if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {
av_log_ask_for_sample(avctx, "unsupported ADX format\n");
return AVERROR_PATCHWELCOME;
}
/* channels */
avctx->channels = buf[7];
if (avctx->channels > 2)
return AVERROR_INVALIDDATA;
/* sample rate */
avctx->sample_rate = AV_RB32(buf + 8);
if (avctx->sample_rate < 1 ||
avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
return AVERROR_INVALIDDATA;
/* bit rate */
avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
/* LPC coefficients */
if (coeff) {
cutoff = AV_RB16(buf + 16);
ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, coeff);
}
*header_size = offset;
return 0;
}
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