PeerStreamer

/*

 * 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

 * 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 avc          a pointer to an arbitrary struct of which the first

 *                     field is a pointer to an AVClass struct

 * @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(void *avc,

                                                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 IIR filtering on signed 16-bit 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);

/**

 * Perform IIR filtering on floating-point 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_flt(const struct FFIIRFilterCoeffs *coeffs,

                       struct FFIIRFilterState *state, int size,

                       const float *src, int sstep, void *dst, int dstep);

#endif /* AVCODEC_IIRFILTER_H */