adx.c
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1 /*
2  * Copyright (c) 2011 Justin Ruggles
3  *
4  * This file is part of Libav.
5  *
6  * Libav 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  * Libav 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 Libav; 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/intreadwrite.h"
22 #include "libavutil/mathematics.h"
23 #include "adx.h"
24 
25 void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
26 {
27  double a, b, c;
28 
29  a = M_SQRT2 - cos(2.0 * M_PI * cutoff / sample_rate);
30  b = M_SQRT2 - 1.0;
31  c = (a - sqrt((a + b) * (a - b))) / b;
32 
33  coeff[0] = lrintf(c * 2.0 * (1 << bits));
34  coeff[1] = lrintf(-(c * c) * (1 << bits));
35 }
36 
37 int avpriv_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf,
38  int bufsize, int *header_size, int *coeff)
39 {
40  int offset, cutoff;
41 
42  if (bufsize < 24)
43  return AVERROR_INVALIDDATA;
44 
45  if (AV_RB16(buf) != 0x8000)
46  return AVERROR_INVALIDDATA;
47  offset = AV_RB16(buf + 2) + 4;
48 
49  /* if copyright string is within the provided data, validate it */
50  if (bufsize >= offset && offset >= 6 && memcmp(buf + offset - 6, "(c)CRI", 6))
51  return AVERROR_INVALIDDATA;
52 
53  /* check for encoding=3 block_size=18, sample_size=4 */
54  if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {
55  av_log_ask_for_sample(avctx, "unsupported ADX format\n");
56  return AVERROR_PATCHWELCOME;
57  }
58 
59  /* channels */
60  avctx->channels = buf[7];
61  if (avctx->channels <= 0 || avctx->channels > 2)
62  return AVERROR_INVALIDDATA;
63 
64  /* sample rate */
65  avctx->sample_rate = AV_RB32(buf + 8);
66  if (avctx->sample_rate < 1 ||
67  avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
68  return AVERROR_INVALIDDATA;
69 
70  /* bit rate */
71  avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
72 
73  /* LPC coefficients */
74  if (coeff) {
75  cutoff = AV_RB16(buf + 16);
76  ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, coeff);
77  }
78 
79  *header_size = offset;
80  return 0;
81 }