libavcodec/iirfilter.h

   1 /*
   2  * IIR filter
   3  * Copyright (c) 2008 Konstantin Shishkov
   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 /**
  23  * @file iirfilter.h
  24  * IIR filter interface
  25  */
  26
  27 #ifndef AVCODEC_IIRFILTER_H
  28 #define AVCODEC_IIRFILTER_H
  29
  30 #include "avcodec.h"
  31
  32 struct FFIIRFilterCoeffs;
  33 struct FFIIRFilterState;
  34
  35 enum IIRFilterType{
  36     FF_FILTER_TYPE_BESSEL,
  37     FF_FILTER_TYPE_BUTTERWORTH,
  38     FF_FILTER_TYPE_CHEBYSHEV,
  39     FF_FILTER_TYPE_ELLIPTIC,
  40 };
  41
  42 enum IIRFilterMode{
  43     FF_FILTER_MODE_LOWPASS,
  44     FF_FILTER_MODE_HIGHPASS,
  45     FF_FILTER_MODE_BANDPASS,
  46     FF_FILTER_MODE_BANDSTOP,
  47 };
  48
  49 /**
  50  * Initialize filter coefficients.
  51  *
  52  * @param filt_type    filter type (e.g. Butterworth)
  53  * @param filt_mode    filter mode (e.g. lowpass)
  54  * @param order        filter order
  55  * @param cutoff_ratio cutoff to input frequency ratio
  56  * @param stopband     stopband to input frequency ratio (used by bandpass and bandstop filter modes)
  57  * @param ripple       ripple factor (used only in Chebyshev filters)
  58  *
  59  * @return pointer to filter coefficients structure or NULL if filter cannot be created
  60  */
  61 struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
  62                                                     enum IIRFilterMode filt_mode,
  63                                                     int order, float cutoff_ratio,
  64                                                     float stopband, float ripple);
  65
  66 /**
  67  * Create new filter state.
  68  *
  69  * @param order filter order
  70  *
  71  * @return pointer to new filter state or NULL if state creation fails
  72  */
  73 struct FFIIRFilterState* ff_iir_filter_init_state(int order);
  74
  75 /**
  76  * Free filter coefficients.
  77  *
  78  * @param coeffs pointer allocated with ff_iir_filter_init_coeffs()
  79  */
  80 void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs);
  81
  82 /**
  83  * Free filter state.
  84  *
  85  * @param state pointer allocated with ff_iir_filter_init_state()
  86  */
  87 void ff_iir_filter_free_state(struct FFIIRFilterState *state);
  88
  89 /**
  90  * Perform lowpass filtering on input samples.
  91  *
  92  * @param coeffs pointer to filter coefficients
  93  * @param state  pointer to filter state
  94  * @param size   input length
  95  * @param src    source samples
  96  * @param sstep  source stride
  97  * @param dst    filtered samples (destination may be the same as input)
  98  * @param dstep  destination stride
  99  */
 100 void ff_iir_filter(const struct FFIIRFilterCoeffs *coeffs, struct FFIIRFilterState *state,
 101                    int size, const int16_t *src, int sstep, int16_t *dst, int dstep);
 102
 103 #endif /* AVCODEC_IIRFILTER_H */