FFmpeg  4.0
opusenc_utils.h
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1 /*
2  * Opus encoder
3  * Copyright (c) 2017 Rostislav Pehlivanov <atomnuker@gmail.com>
4  *
5  * This file is part of FFmpeg.
6  *
7  * FFmpeg is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU Lesser General Public
9  * License as published by the Free Software Foundation; either
10  * version 2.1 of the License, or (at your option) any later version.
11  *
12  * FFmpeg is distributed in the hope that it will be useful,
13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15  * Lesser General Public License for more details.
16  *
17  * You should have received a copy of the GNU Lesser General Public
18  * License along with FFmpeg; if not, write to the Free Software
19  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
20  */
21 
22 #ifndef AVCODEC_OPUSENC_UTILS_H
23 #define AVCODEC_OPUSENC_UTILS_H
24 
25 #include "opus.h"
26 
27 typedef struct FFBesselFilter {
28  float a[3];
29  float b[2];
30  float x[3];
31  float y[3];
33 
34 /* Fills the coefficients, returns 1 if filter will be unstable */
35 static inline int bessel_reinit(FFBesselFilter *s, float n, float f0, float fs,
36  int highpass)
37 {
38  int unstable;
39  float c, cfreq, w0, k1, k2;
40 
41  if (!highpass) {
42  c = (1.0f/sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f))/sqrtf(3.0f);
43  cfreq = c*f0/fs;
44  unstable = (cfreq <= 0.0f || cfreq >= 1.0f/4.0f);
45  } else {
46  c = sqrtf(3.0f)*sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f);
47  cfreq = 0.5f - c*f0/fs;
48  unstable = (cfreq <= 3.0f/8.0f || cfreq >= 1.0f/2.0f);
49  }
50 
51  w0 = tanf(M_PI*cfreq);
52  k1 = 3.0f * w0;
53  k2 = 3.0f * w0;
54 
55  s->a[0] = k2/(1.0f + k1 + k2);
56  s->a[1] = 2.0f * s->a[0];
57  s->a[2] = s->a[0];
58  s->b[0] = 2.0f * s->a[0] * (1.0f/k2 - 1.0f);
59  s->b[1] = 1.0f - (s->a[0] + s->a[1] + s->a[2] + s->b[0]);
60 
61  if (highpass) {
62  s->a[1] *= -1;
63  s->b[0] *= -1;
64  }
65 
66  return unstable;
67 }
68 
69 static inline int bessel_init(FFBesselFilter *s, float n, float f0, float fs,
70  int highpass)
71 {
72  memset(s, 0, sizeof(FFBesselFilter));
73  return bessel_reinit(s, n, f0, fs, highpass);
74 }
75 
76 static inline float bessel_filter(FFBesselFilter *s, float x)
77 {
78  s->x[2] = s->x[1];
79  s->x[1] = s->x[0];
80  s->x[0] = x;
81  s->y[2] = s->y[1];
82  s->y[1] = s->y[0];
83  s->y[0] = s->a[0]*s->x[0] + s->a[1]*s->x[1] + s->a[2]*s->x[2] + s->b[0]*s->y[1] + s->b[1]*s->y[2];
84  return s->y[0];
85 }
86 
87 #endif /* AVCODEC_OPUSENC_UTILS_H */
const char * s
Definition: avisynth_c.h:768
static int bessel_reinit(FFBesselFilter *s, float n, float f0, float fs, int highpass)
Definition: opusenc_utils.h:35
static float bessel_filter(FFBesselFilter *s, float x)
Definition: opusenc_utils.h:76
int n
Definition: avisynth_c.h:684
static int bessel_init(FFBesselFilter *s, float n, float f0, float fs, int highpass)
Definition: opusenc_utils.h:69
static double c[64]
#define M_PI
Definition: mathematics.h:52