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/*
* IIR filter
* Copyright (c) 2008 Konstantin Shishkov
*
* 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
*/
/**
* @file iirfilter.h
* IIR filter interface
*/
#ifndef AVCODEC_IIRFILTER_H
#define AVCODEC_IIRFILTER_H
#include "avcodec.h"
struct FFIIRFilterCoeffs;
struct FFIIRFilterState;
enum IIRFilterType{
FF_FILTER_TYPE_BESSEL,
FF_FILTER_TYPE_BUTTERWORTH,
FF_FILTER_TYPE_CHEBYSHEV,
FF_FILTER_TYPE_ELLIPTIC,
};
enum IIRFilterMode{
FF_FILTER_MODE_LOWPASS,
FF_FILTER_MODE_HIGHPASS,
FF_FILTER_MODE_BANDPASS,
FF_FILTER_MODE_BANDSTOP,
};
/**
* Initialize filter coefficients.
*
* @param filt_type filter type (e.g. Butterworth)
* @param filt_mode filter mode (e.g. lowpass)
* @param order filter order
* @param cutoff_ratio cutoff to input frequency ratio
* @param stopband stopband to input frequency ratio (used by bandpass and bandstop filter modes)
* @param ripple ripple factor (used only in Chebyshev filters)
*
* @return pointer to filter coefficients structure or NULL if filter cannot be created
*/
struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
enum IIRFilterMode filt_mode,
int order, float cutoff_ratio,
float stopband, float ripple);
/**
* Create new filter state.
*
* @param order filter order
*
* @return pointer to new filter state or NULL if state creation fails
*/
struct FFIIRFilterState* ff_iir_filter_init_state(int order);
/**
* Free filter coefficients.
*
* @param coeffs pointer allocated with ff_iir_filter_init_coeffs()
*/
void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs);
/**
* Free filter state.
*
* @param state pointer allocated with ff_iir_filter_init_state()
*/
void ff_iir_filter_free_state(struct FFIIRFilterState *state);
/**
* Perform lowpass filtering on input samples.
*
* @param coeffs pointer to filter coefficients
* @param state pointer to filter state
* @param size input length
* @param src source samples
* @param sstep source stride
* @param dst filtered samples (destination may be the same as input)
* @param dstep destination stride
*/
void ff_iir_filter(const struct FFIIRFilterCoeffs *coeffs, struct FFIIRFilterState *state,
int size, const int16_t *src, int sstep, int16_t *dst, int dstep);
#endif /* AVCODEC_IIRFILTER_H */
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