[FFmpeg-devel] [PATCH] Lowpass functionality for lavc
Kostya
kostya.shishkov
Sat Aug 16 12:12:36 CEST 2008
On Fri, Aug 15, 2008 at 09:37:07PM +0200, Michael Niedermayer wrote:
[...]
> >
> > /**
> > * Free filter coefficients.
> > *
> > * @param coeffs pointer allocated with ff_lowpass_filter_init_coeffs()
> > */
> > void ff_lowpass_filter_free_coeffs(struct FFLPFilterCoeffs *coeffs);
> >
> > /**
> > * Free filter state.
> > *
> > * @param state pointer allocated with ff_lowpass_filter_init_state()
> > */
> > void ff_lowpass_filter_free_state(struct FFLPFilterState *state);
>
> we do not need wrapers around av_free()
> this is not public API where it would be hard to replace later
So I made FFLPFilterState const for now and #if 0'd free funcs.
Better implementation will allocate arrays for states depending on order,
so more complicated free function will be needed.
[...]
> > /*
> > * Lowpass IIR filter
>
> actually, this could do more generic IIR filtering one day ...
*sigh* indeed. After I deal with AAC and RV I will read filter theory
and do that. Too bad I didn't have time to do it earlier.
[...]
> > static const float lp_filter_data[][LOWPASS_FILTER_ORDER+2] = {
> > { 0.5000000000, 9.398085e-01, -0.0176648009, 0.0000000000, -0.4860288221, 0.0000000000 },
> > { 0.4535147392, 6.816645e-01, -0.4646665999, -2.2127207402, -3.9912017501, -3.2380429984 },
> > { 0.4166666667, 4.998150e-01, -0.2498216698, -1.3392807613, -2.7693097862, -2.6386277439 },
> > { 0.3628117914, 3.103469e-01, -0.0965076902, -0.5977763360, -1.4972580903, -1.7740085241 },
> > { 0.3333333333, 2.346995e-01, -0.0557639007, -0.3623690447, -1.0304538354, -1.3066051440 },
> > { 0.2916666667, 1.528432e-01, -0.0261686639, -0.1473794606, -0.6204721225, -0.6514716536 },
> > { 0.2267573696, 6.917529e-02, -0.0202414073, 0.0780167640, -0.5277442247, 0.3631641670 },
> > { 0.2187500000, 6.178391e-02, -0.0223681543, 0.1069446609, -0.5615167033, 0.4883976841 },
> > { 0.2083333333, 5.298685e-02, -0.0261686639, 0.1473794606, -0.6204721225, 0.6514716536 },
> > { 0.1587301587, 2.229030e-02, -0.0647354087, 0.4172275190, -1.1412129810, 1.4320761385 },
> > { 0.1458333333, 1.693903e-02, -0.0823177861, 0.5192354923, -1.3444768251, 1.6365345642 },
> > { 0.1133786848, 7.374053e-03, -0.1481421788, 0.8650973862, -1.9894244796, 2.1544844308 },
> > { 0.1041666667, 5.541768e-03, -0.1742301048, 0.9921936565, -2.2090801108, 2.3024482658 },
> > };
>
> an array of FFLPFilterCoeffs makes more sense i think
Indeed, and init_coeffs() return a pointer in it now (hence the const qualifier).
[...]
> you are mixing float and int, iam not sure if this is ideal, at least
> the float->int convertion should use lrintf()
I'm not sure that fixed-point filter is a good idea and only output is
converted from float (with lrintf() now).
> [...]
> --
> Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> I have never wished to cater to the crowd; for what I know they do not
> approve, and what they approve I do not know. -- Epicurus
-------------- next part --------------
/*
* Lowpass 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 lowpass.h
* lowpass filter interface
*/
#ifndef FFMPEG_LOWPASS_H
#define FFMPEG_LOWPASS_H
#include "avcodec.h"
struct FFLPFilterCoeffs;
struct FFLPFilterState;
/**
* Initialize filter coefficients.
*
* @param order filter order
* @param cutoff_ratio cutoff to input frequency ratio
*
* @return pointer to filter coefficients structure or NULL if filter cannot be created
*/
const struct FFLPFilterCoeffs* ff_lowpass_filter_init_coeffs(int order, float cutoff_ratio);
/**
* Create new filter state.
*
* @param order filter order
*
* @return pointer to new filter state or NULL if state creation fails
*/
struct FFLPFilterState* ff_lowpass_filter_init_state(int order);
#if 0 //enable with arbitrary order filter implementation, use av_free() for filter state only for now
/**
* Free filter coefficients.
*
* @param coeffs pointer allocated with ff_lowpass_filter_init_coeffs()
*/
void ff_lowpass_filter_free_coeffs(struct FFLPFilterCoeffs *coeffs);
/**
* Free filter state.
*
* @param state pointer allocated with ff_lowpass_filter_init_state()
*/
void ff_lowpass_filter_free_state(struct FFLPFilterState *state);
#endif
/**
* 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_lowpass_filter(const struct FFLPFilterCoeffs *coeffs, struct FFLPFilterState *state, int size, int16_t *src, int sstep, int16_t *dst, int dstep);
#endif /* FFMPEG_LOWPASS_H */
-------------- next part --------------
/*
* Lowpass 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 lowpass.c
* lowpass filter implementation
*/
#include "lowpass.h"
/**********************
* TODO:
* support filters with order != 4
* calculate coefficients for filter instead of taking approximate ones from the table
*********************/
/** filter order */
#define LOWPASS_FILTER_ORDER 4
/**
* IIR filter global parameters
*/
typedef struct FFLPFilterCoeffs{
float gain;
float c[LOWPASS_FILTER_ORDER];
}FFLPFilterCoeffs;
/**
* filter data for 4th order IIR lowpass Butterworth filter
*/
static const FFLPFilterCoeffs lp_filter_coeffs[] = {
{ 9.398085e-01, { -0.0176648009, 0.0000000000, -0.4860288221, 0.0000000000 } },
{ 6.816645e-01, { -0.4646665999, -2.2127207402, -3.9912017501, -3.2380429984 } },
{ 4.998150e-01, { -0.2498216698, -1.3392807613, -2.7693097862, -2.6386277439 } },
{ 3.103469e-01, { -0.0965076902, -0.5977763360, -1.4972580903, -1.7740085241 } },
{ 2.346995e-01, { -0.0557639007, -0.3623690447, -1.0304538354, -1.3066051440 } },
{ 1.528432e-01, { -0.0261686639, -0.1473794606, -0.6204721225, -0.6514716536 } },
{ 6.917529e-02, { -0.0202414073, 0.0780167640, -0.5277442247, 0.3631641670 } },
{ 6.178391e-02, { -0.0223681543, 0.1069446609, -0.5615167033, 0.4883976841 } },
{ 5.298685e-02, { -0.0261686639, 0.1473794606, -0.6204721225, 0.6514716536 } },
{ 2.229030e-02, { -0.0647354087, 0.4172275190, -1.1412129810, 1.4320761385 } },
{ 1.693903e-02, { -0.0823177861, 0.5192354923, -1.3444768251, 1.6365345642 } },
{ 7.374053e-03, { -0.1481421788, 0.8650973862, -1.9894244796, 2.1544844308 } },
{ 5.541768e-03, { -0.1742301048, 0.9921936565, -2.2090801108, 2.3024482658 } },
};
/** cutoff ratios for lp_filter_data[] */
static const float lp_cutoff_ratios[] = {
0.5000000000, 0.4535147392, 0.4166666667, 0.3628117914,
0.3333333333, 0.2916666667, 0.2267573696, 0.2187500000,
0.2083333333, 0.1587301587, 0.1458333333, 0.1133786848,
0.1041666667,
};
/**
* IIR filter state
*/
typedef struct FFLPFilterState{
float x[LOWPASS_FILTER_ORDER];
float y[LOWPASS_FILTER_ORDER];
}FFLPFilterState;
const struct FFLPFilterCoeffs* ff_lowpass_filter_init_coeffs(int order, float cutoff_ratio)
{
int i, j, size;
//we can create only order-4 filters with cutoff ratio <= 0.5 for now
if(order != LOWPASS_FILTER_ORDER) return NULL;
size = sizeof(lp_cutoff_ratios) / sizeof(lp_cutoff_ratios[0]);
if(cutoff_ratio > lp_cutoff_ratios[0])
return NULL;
for(i = 0; i < size; i++){
if(cutoff_ratio >= lp_cutoff_ratios[i])
break;
}
if(i == size)
i = size - 1;
return &lp_filter_coeffs[i];
}
struct FFLPFilterState* ff_lowpass_filter_init_state(int order)
{
if(order != LOWPASS_FILTER_ORDER) return NULL;
return av_mallocz(sizeof(FFLPFilterState));
}
#define FILTER(i0, i1, i2, i3) \
in = *src * c->gain; \
res = (s->x[i0] + in )*1 \
+ (s->x[i1] + s->x[i3])*4 \
+ s->x[i2] *6 \
+ c->c[0]*s->y[i0] + c->c[1]*s->y[i1] \
+ c->c[2]*s->y[i2] + c->c[3]*s->y[i3]; \
*dst = av_clip_int16(lrintf(res)); \
s->x[i0] = in; \
s->y[i0] = res; \
src += sstep; \
dst += dstep; \
void ff_lowpass_filter(const struct FFLPFilterCoeffs *c, struct FFLPFilterState *s, int size, int16_t *src, int sstep, int16_t *dst, int dstep)
{
int i, j;
float in, res;
for(i = 0; i < size; i += 4){
FILTER(0, 1, 2, 3);
FILTER(1, 2, 3, 0);
FILTER(2, 3, 0, 1);
FILTER(3, 0, 1, 2);
}
}
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