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