[FFmpeg-devel] [PATCH] Lowpass functionality for lavc
Michael Niedermayer
michaelni
Fri Aug 15 21:37:07 CEST 2008
On Fri, Aug 15, 2008 at 08:43:15PM +0300, Kostya wrote:
> 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
> /*
> * 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
ok
> * @param coeffs filter coefficients
no such parameter
> * @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);
freq and cutoff are redundant relative to each other, only the ratio should
be needed
>
> /**
> * 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);
ok
>
> /**
> * 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
>
> /**
> * 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 */
>
ok
> /*
> * Lowpass IIR filter
actually, this could do more generic IIR filtering one day ...
> * 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
>
ok
> /**
> * 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 },
> };
an array of FFLPFilterCoeffs makes more sense i think
>
> /**
> * 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;
ok
>
> 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));
> }
ok
>
> 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);
> }
> }
you are mixing float and int, iam not sure if this is ideal, at least
the float->int convertion should use lrintf()
[...]
--
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
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