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/*
* Opus encoder
* Copyright (c) 2017 Rostislav Pehlivanov <atomnuker@gmail.com>
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef AVCODEC_OPUSENC_UTILS_H
#define AVCODEC_OPUSENC_UTILS_H
#include "opus.h"
typedef struct FFBesselFilter {
float a[3];
float b[2];
float x[3];
float y[3];
} FFBesselFilter;
/* Fills the coefficients, returns 1 if filter will be unstable */
static inline int bessel_reinit(FFBesselFilter *s, float n, float f0, float fs,
int highpass)
{
int unstable;
float c, cfreq, w0, k1, k2;
if (!highpass) {
c = (1.0f/sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f))/sqrtf(3.0f);
cfreq = c*f0/fs;
unstable = (cfreq <= 0.0f || cfreq >= 1.0f/4.0f);
} else {
c = sqrtf(3.0f)*sqrtf(sqrtf(pow(2.0f, 1.0f/n) - 3.0f/4.0f) - 0.5f);
cfreq = 0.5f - c*f0/fs;
unstable = (cfreq <= 3.0f/8.0f || cfreq >= 1.0f/2.0f);
}
w0 = tanf(M_PI*cfreq);
k1 = 3.0f * w0;
k2 = 3.0f * w0;
s->a[0] = k2/(1.0f + k1 + k2);
s->a[1] = 2.0f * s->a[0];
s->a[2] = s->a[0];
s->b[0] = 2.0f * s->a[0] * (1.0f/k2 - 1.0f);
s->b[1] = 1.0f - (s->a[0] + s->a[1] + s->a[2] + s->b[0]);
if (highpass) {
s->a[1] *= -1;
s->b[0] *= -1;
}
return unstable;
}
static inline int bessel_init(FFBesselFilter *s, float n, float f0, float fs,
int highpass)
{
memset(s, 0, sizeof(FFBesselFilter));
return bessel_reinit(s, n, f0, fs, highpass);
}
static inline float bessel_filter(FFBesselFilter *s, float x)
{
s->x[2] = s->x[1];
s->x[1] = s->x[0];
s->x[0] = x;
s->y[2] = s->y[1];
s->y[1] = s->y[0];
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];
return s->y[0];
}
#endif /* AVCODEC_OPUSENC_UTILS_H */
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