FFmpeg
adx.c
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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 ff_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 copyright string is within the provided data, validate it */
51  if (bufsize >= offset && offset >= 6 && memcmp(buf + offset - 6, "(c)CRI", 6))
52  return AVERROR_INVALIDDATA;
53 
54  /* check for encoding=3 block_size=18, sample_size=4 */
55  if (buf[4] != 3 || buf[5] != 18 || buf[6] != 4) {
56  avpriv_request_sample(avctx, "Support for this ADX format");
57  return AVERROR_PATCHWELCOME;
58  }
59 
60  /* channels */
61  avctx->channels = buf[7];
62  if (avctx->channels <= 0 || avctx->channels > 2)
63  return AVERROR_INVALIDDATA;
64 
65  /* sample rate */
66  avctx->sample_rate = AV_RB32(buf + 8);
67  if (avctx->sample_rate < 1 ||
68  avctx->sample_rate > INT_MAX / (avctx->channels * BLOCK_SIZE * 8))
69  return AVERROR_INVALIDDATA;
70 
71  /* bit rate */
72  avctx->bit_rate = avctx->sample_rate * avctx->channels * BLOCK_SIZE * 8 / BLOCK_SAMPLES;
73 
74  /* LPC coefficients */
75  if (coeff) {
76  cutoff = AV_RB16(buf + 16);
77  ff_adx_calculate_coeffs(cutoff, avctx->sample_rate, COEFF_BITS, coeff);
78  }
79 
80  *header_size = offset;
81  return 0;
82 }
AVCodecContext::sample_rate
int sample_rate
samples per second
Definition: avcodec.h:992
b
#define b
Definition: input.c:40
mathematics.h
sample_rate
sample_rate
Definition: ffmpeg_filter.c:153
intreadwrite.h
BLOCK_SAMPLES
#define BLOCK_SAMPLES
Definition: adx.h:54
bits
uint8_t bits
Definition: vp3data.h:141
AVERROR_PATCHWELCOME
#define AVERROR_PATCHWELCOME
Not yet implemented in FFmpeg, patches welcome.
Definition: error.h:64
AVCodecContext::bit_rate
int64_t bit_rate
the average bitrate
Definition: avcodec.h:433
c
Undefined Behavior In the C some operations are like signed integer dereferencing freed accessing outside allocated Undefined Behavior must not occur in a C it is not safe even if the output of undefined operations is unused The unsafety may seem nit picking but Optimizing compilers have in fact optimized code on the assumption that no undefined Behavior occurs Optimizing code based on wrong assumptions can and has in some cases lead to effects beyond the output of computations The signed integer overflow problem in speed critical code Code which is highly optimized and works with signed integers sometimes has the problem that often the output of the computation does not c
Definition: undefined.txt:32
ff_adx_calculate_coeffs
void ff_adx_calculate_coeffs(int cutoff, int sample_rate, int bits, int *coeff)
Calculate LPC coefficients based on cutoff frequency and sample rate.
Definition: adx.c:26
AV_RB32
uint64_t_TMPL AV_WL64 unsigned int_TMPL AV_WL32 unsigned int_TMPL AV_WL24 unsigned int_TMPL AV_WL16 uint64_t_TMPL AV_WB64 unsigned int_TMPL AV_RB32
Definition: bytestream.h:96
a
The reader does not expect b to be semantically here and if the code is changed by maybe adding a a division or other the signedness will almost certainly be mistaken To avoid this confusion a new type was SUINT is the C unsigned type but it holds a signed int to use the same example SUINT a
Definition: undefined.txt:41
offset
it s the only field you need to keep assuming you have a context There is some magic you don t need to care about around this just let it vf offset
Definition: writing_filters.txt:86
M_PI
#define M_PI
Definition: mathematics.h:52
AVCodecContext::channels
int channels
number of audio channels
Definition: avcodec.h:993
lrintf
#define lrintf(x)
Definition: libm_mips.h:72
common.h
AVCodecContext
main external API structure.
Definition: avcodec.h:383
COEFF_BITS
#define COEFF_BITS
Definition: adx.h:51
adx.h
avpriv_request_sample
#define avpriv_request_sample(...)
Definition: tableprint_vlc.h:37
M_SQRT2
#define M_SQRT2
Definition: mathematics.h:61
coeff
static const double coeff[2][5]
Definition: vf_owdenoise.c:78
AVERROR_INVALIDDATA
#define AVERROR_INVALIDDATA
Invalid data found when processing input.
Definition: error.h:61
BLOCK_SIZE
#define BLOCK_SIZE
Definition: adx.h:53
ff_adx_decode_header
int ff_adx_decode_header(AVCodecContext *avctx, const uint8_t *buf, int bufsize, int *header_size, int *coeff)
Decode ADX stream header.
Definition: adx.c:38
AV_RB16
uint64_t_TMPL AV_WL64 unsigned int_TMPL AV_WL32 unsigned int_TMPL AV_WL24 unsigned int_TMPL AV_WL16 uint64_t_TMPL AV_WB64 unsigned int_TMPL AV_WB32 unsigned int_TMPL AV_WB24 unsigned int_TMPL AV_RB16
Definition: bytestream.h:98
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