yading@10: /*
yading@10:  * Copyright (c) 2011  Justin Ruggles
yading@10:  *
yading@10:  * This file is part of Libav.
yading@10:  *
yading@10:  * Libav is free software; you can redistribute it and/or
yading@10:  * modify it under the terms of the GNU Lesser General Public
yading@10:  * License as published by the Free Software Foundation; either
yading@10:  * version 2.1 of the License, or (at your option) any later version.
yading@10:  *
yading@10:  * Libav is distributed in the hope that it will be useful,
yading@10:  * but WITHOUT ANY WARRANTY; without even the implied warranty of
yading@10:  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
yading@10:  * Lesser General Public License for more details.
yading@10:  *
yading@10:  * You should have received a copy of the GNU Lesser General Public
yading@10:  * License along with Libav; if not, write to the Free Software
yading@10:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
yading@10:  */
yading@10: 
yading@10: #include "libavutil/common.h"
yading@10: #include "libavutil/intreadwrite.h"
yading@10: #include "libavutil/mathematics.h"
yading@10: #include "adx.h"
yading@10: 
yading@10: void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
yading@10: {
yading@10:     double a, b, c;
yading@10: 
yading@10:     a = M_SQRT2 - cos(2.0 * M_PI * cutoff / sample_rate);
yading@10:     b = M_SQRT2 - 1.0;
yading@10:     c = (a - sqrt((a + b) * (a - b))) / b;
yading@10: 
yading@10:     coeff[0] = lrintf(c * 2.0  * (1 << bits));
yading@10:     coeff[1] = lrintf(-(c * c) * (1 << bits));
yading@10: }
yading@10: 
yading@10: int avpriv_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf,
yading@10:                              int bufsize, int *header_size, int *coeff)
yading@10: {
yading@10:     int offset, cutoff;
yading@10: 
yading@10:     if (bufsize < 24)
yading@10:         return AVERROR_INVALIDDATA;
yading@10: 
yading@10:     if (AV_RB16(buf) != 0x8000)
yading@10:         return AVERROR_INVALIDDATA;
yading@10:     offset = AV_RB16(buf + 2) + 4;
yading@10: 
yading@10:     if (offset < 6) {
yading@10:         av_log(avctx, AV_LOG_ERROR, "offset is prior data\n");
yading@10:         return AVERROR_INVALIDDATA;
yading@10:     }
yading@10: 
yading@10:     /* if copyright string is within the provided data, validate it */
yading@10:     if (bufsize >= offset && memcmp(buf + offset - 6, "(c)CRI", 6))
yading@10:         return AVERROR_INVALIDDATA;
yading@10: 
yading@10:     /* check for encoding=3 block_size=18, sample_size=4 */
yading@10:     if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {
yading@10:         avpriv_request_sample(avctx, "Support for this ADX format");
yading@10:         return AVERROR_PATCHWELCOME;
yading@10:     }
yading@10: 
yading@10:     /* channels */
yading@10:     avctx->channels = buf[7];
yading@10:     if (avctx->channels <= 0 || avctx->channels > 2)
yading@10:         return AVERROR_INVALIDDATA;
yading@10: 
yading@10:     /* sample rate */
yading@10:     avctx->sample_rate = AV_RB32(buf + 8);
yading@10:     if (avctx->sample_rate < 1 ||
yading@10:         avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
yading@10:         return AVERROR_INVALIDDATA;
yading@10: 
yading@10:     /* bit rate */
yading@10:     avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
yading@10: 
yading@10:     /* LPC coefficients */
yading@10:     if (coeff) {
yading@10:         cutoff = AV_RB16(buf + 16);
yading@10:         ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, coeff);
yading@10:     }
yading@10: 
yading@10:     *header_size = offset;
yading@10:     return 0;
yading@10: }