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  1. /*
  2.  * Copyright (c) 2011  Justin Ruggles
  3.  *
  4.  * This file is part of FFmpeg.
  5.  *
  6.  * FFmpeg is free software; you can redistribute it and/or
  7.  * modify it under the terms of the GNU Lesser General Public
  8.  * License as published by the Free Software Foundation; either
  9.  * version 2.1 of the License, or (at your option) any later version.
  10.  *
  11.  * FFmpeg is distributed in the hope that it will be useful,
  12.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14.  * Lesser General Public License for more details.
  15.  *
  16.  * You should have received a copy of the GNU Lesser General Public
  17.  * License along with FFmpeg; if not, write to the Free Software
  18.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19.  */
  20.  
  21. #include "libavutil/common.h"
  22. #include "libavutil/intreadwrite.h"
  23. #include "libavutil/mathematics.h"
  24. #include "adx.h"
  25.  
  26. void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
  27. {
  28.     double a, b, c;
  29.  
  30.     a = M_SQRT2 - cos(2.0 * M_PI * cutoff / sample_rate);
  31.     b = M_SQRT2 - 1.0;
  32.     c = (a - sqrt((a + b) * (a - b))) / b;
  33.  
  34.     coeff[0] = lrintf(c * 2.0  * (1 << bits));
  35.     coeff[1] = lrintf(-(c * c) * (1 << bits));
  36. }
  37.  
  38. int avpriv_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf,
  39.                              int bufsize, int *header_size, int *coeff)
  40. {
  41.     int offset, cutoff;
  42.  
  43.     if (bufsize < 24)
  44.         return AVERROR_INVALIDDATA;
  45.  
  46.     if (AV_RB16(buf) != 0x8000)
  47.         return AVERROR_INVALIDDATA;
  48.     offset = AV_RB16(buf + 2) + 4;
  49.  
  50.     if (offset < 6) {
  51.         av_log(avctx, AV_LOG_ERROR, "offset is prior data\n");
  52.         return AVERROR_INVALIDDATA;
  53.     }
  54.  
  55.     /* if copyright string is within the provided data, validate it */
  56.     if (bufsize >= offset && memcmp(buf + offset - 6, "(c)CRI", 6))
  57.         return AVERROR_INVALIDDATA;
  58.  
  59.     /* check for encoding=3 block_size=18, sample_size=4 */
  60.     if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {
  61.         avpriv_request_sample(avctx, "Support for this ADX format");
  62.         return AVERROR_PATCHWELCOME;
  63.     }
  64.  
  65.     /* channels */
  66.     avctx->channels = buf[7];
  67.     if (avctx->channels <= 0 || avctx->channels > 2)
  68.         return AVERROR_INVALIDDATA;
  69.  
  70.     /* sample rate */
  71.     avctx->sample_rate = AV_RB32(buf + 8);
  72.     if (avctx->sample_rate < 1 ||
  73.         avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
  74.         return AVERROR_INVALIDDATA;
  75.  
  76.     /* bit rate */
  77.     avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
  78.  
  79.     /* LPC coefficients */
  80.     if (coeff) {
  81.         cutoff = AV_RB16(buf + 16);
  82.         ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, coeff);
  83.     }
  84.  
  85.     *header_size = offset;
  86.     return 0;
  87. }
  88.