[FFmpeg-devel] [PATCH] Lowpass functionality for lavc
Kostya
kostya.shishkov
Fri Aug 15 19:43:15 CEST 2008
On Thu, Aug 14, 2008 at 04:40:27PM +0200, Michael Niedermayer wrote:
[...]
>
> > /**
> > * Initialize filter coefficients.
> > *
> > * @param coeffs filter coefficients
> > * @param freq input frequency (sample rate/2)
> > * @param cutoff cutoff frequency
> > *
> > * @return pointer to filter coefficients structure or NULL if filter cannot be created
> > */
> > void* ff_lowpass_filter_init_coeffs(int order, int freq, int cutoff);
>
> it should have some type not void* (and yes it can be done without putting the
> whole struct in the header see libavutil/*.h)
> you also forget to docuent order not that this is imporatnt i just noticed
Used the scheme after libavutil/tree.h
[...]
> >
> > void ff_lowpass_filter(void *coeffs, void *state, int size, int16_t *src, int sstep, int16_t *dst, int dstep)
> > {
> > int i, j;
> > float in, res;
> > LPFilterCoeffs *c = (LPFilterCoeffs*)coeffs;
> > LPFilterState *s = (LPFilterState*) state;
> >
> > for(i = 0; i < size; i++, src += sstep, dst += dstep){
> > for(j = 0; j < LOWPASS_FILTER_ORDER - 1; j++){
> > s->x[j] = s->x[j+1];
> > s->y[j] = s->y[j+1];
> > }
>
> luckily iam in good mood
> please unroll the loop and remove this
>
> its supposed to look something like
>
> #define FILTER(a,b,c,d, src)
> s->x[a]= *src++ * c->gain;
> s->y[a]= s->x[a] + 123*s->y[a] + 321*s->y[b] + ...
> *dst++= av_clip_int16(s->y[a]);
>
> FILTER(0,1,2,3)
> FILTER(1,2,3,0)
> FILTER(2,3,0,1)
> FILTER(3,0,1,2)
Here it is.
> [...]
> --
> Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
>
> The misfortune of the wise is better than the prosperity of the fool.
> -- 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 coeffs filter coefficients
* @param freq input frequency (sample rate/2)
* @param cutoff cutoff frequency
*
* @return pointer to filter coefficients structure or NULL if filter cannot be created
*/
struct FFLPFilterCoeffs* ff_lowpass_filter_init_coeffs(int order, int freq, int cutoff);
/**
* 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);
/**
* 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);
/**
* 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(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
/**
* filter data for 4th order IIR lowpass Butterworth filter
*
* data format:
* normalized cutoff frequency | inverse filter gain | coefficients
*/
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 },
};
/**
* IIR filter global parameters
*/
typedef struct FFLPFilterCoeffs{
float gain;
float c[LOWPASS_FILTER_ORDER];
}FFLPFilterCoeffs;
/**
* IIR filter state
*/
typedef struct FFLPFilterState{
float x[LOWPASS_FILTER_ORDER];
float y[LOWPASS_FILTER_ORDER];
}FFLPFilterState;
struct FFLPFilterCoeffs* ff_lowpass_filter_init_coeffs(int order, int freq, int cutoff)
{
int i, j, size;
float cutoff_ratio;
FFLPFilterCoeffs *coeffs;
//we can create only order-4 filters with cutoff ratio <= 0.5 for now
if(order != LOWPASS_FILTER_ORDER) return NULL;
size = sizeof(lp_filter_data) / sizeof(lp_filter_data[0]);
cutoff_ratio = (float)cutoff / freq;
if(cutoff_ratio > lp_filter_data[0][0])
return NULL;
for(i = 0; i < size; i++){
if(cutoff_ratio >= lp_filter_data[i][0])
break;
}
coeffs = (FFLPFilterCoeffs*)av_malloc(sizeof(FFLPFilterCoeffs));
if(i == size)
i = size - 1;
coeffs->gain = lp_filter_data[i][1];
memcpy(coeffs->c, lp_filter_data[i]+2, sizeof(coeffs->c[0])*4);
return coeffs;
}
struct FFLPFilterState* ff_lowpass_filter_init_state(int order)
{
if(order != LOWPASS_FILTER_ORDER) return NULL;
return av_mallocz(sizeof(FFLPFilterState));
}
void ff_lowpass_filter_free_coeffs(struct FFLPFilterCoeffs *coeffs)
{
av_free(coeffs);
}
void ff_lowpass_filter_free_state(struct FFLPFilterState *state)
{
av_free(state);
}
#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(res); \
s->x[i0] = in; \
s->y[i0] = res; \
src += sstep; \
dst += dstep; \
void ff_lowpass_filter(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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