libavcodec/opusenc_utils.h

   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];
  32 } FFBesselFilter;
  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 */