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/*
* Delay Locked Loop based time filter
* Copyright (c) 2009 Samalyse |
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* Copyright (c) 2009 Michael Niedermayer |
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* Author: Olivier Guilyardi <olivier samalyse com> |
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* Michael Niedermayer <michaelni gmx at> |
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*
* 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
*/
|
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#include "libavutil/common.h" |
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#include "libavutil/mem.h" |
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#include "config.h"
#include "timefilter.h"
struct TimeFilter { |
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// Delay Locked Loop data. These variables refer to mathematical
// concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf |
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double cycle_time;
double feedback2_factor;
double feedback3_factor; |
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double clock_period; |
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int count; |
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};
|
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/* 1 - exp(-x) using a 3-order power series */
static double qexpneg(double x)
{
return 1 - 1 / (1 + x * (1 + x / 2 * (1 + x / 3)));
}
TimeFilter *ff_timefilter_new(double time_base,
double period,
double bandwidth) |
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{ |
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TimeFilter *self = av_mallocz(sizeof(TimeFilter)); |
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double o = 2 * M_PI * bandwidth * period * time_base;
self->clock_period = time_base;
self->feedback2_factor = qexpneg(M_SQRT2 * o); |
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self->feedback3_factor = qexpneg(o * o) / period; |
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return self;
}
void ff_timefilter_destroy(TimeFilter *self)
{
av_freep(&self);
}
void ff_timefilter_reset(TimeFilter *self)
{ |
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self->count = 0; |
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}
|
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double ff_timefilter_update(TimeFilter *self, double system_time, double period) |
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{ |
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self->count++; |
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if (self->count == 1) {
self->cycle_time = system_time; |
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} else { |
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double loop_error; |
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self->cycle_time += self->clock_period * period;
loop_error = system_time - self->cycle_time; |
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|
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self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error; |
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self->clock_period += self->feedback3_factor * loop_error; |
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}
return self->cycle_time;
} |
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|
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double ff_timefilter_eval(TimeFilter *self, double delta)
{
return self->cycle_time + self->clock_period * delta;
}
|
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#ifdef TEST |
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#include "libavutil/lfg.h"
#define LFG_MAX ((1LL << 32) - 1)
|
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int main(void)
{ |
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AVLFG prng; |
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double n0, n1; |
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#define SAMPLES 1000
double ideal[SAMPLES];
double samples[SAMPLES]; |
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double samplet[SAMPLES]; |
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for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) {
for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) {
double best_error = 1000000000;
double bestpar0 = 1; |
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double bestpar1 = 1; |
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int better, i;
|
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av_lfg_init(&prng, 123); |
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for (i = 0; i < SAMPLES; i++) { |
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samplet[i] = 10 + i + (av_lfg_get(&prng) < LFG_MAX/2 ? 0 : 0.999);
ideal[i] = samplet[i] + n1 * i / (1000); |
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samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2) / (LFG_MAX * 10LL); |
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if(i && samples[i]<samples[i-1])
samples[i]=samples[i-1]+0.001; |
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}
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do { |
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double par0, par1; |
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better = 0;
for (par0 = bestpar0 * 0.8; par0 <= bestpar0 * 1.21; par0 += bestpar0 * 0.05) {
for (par1 = bestpar1 * 0.8; par1 <= bestpar1 * 1.21; par1 += bestpar1 * 0.05) {
double error = 0;
TimeFilter *tf = ff_timefilter_new(1, par0, par1);
for (i = 0; i < SAMPLES; i++) { |
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double filtered; |
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filtered = ff_timefilter_update(tf, samples[i], i ? (samplet[i] - samplet[i-1]) : 1);
if(filtered < 0 || filtered > 1000000000)
printf("filter is unstable\n"); |
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error += (filtered - ideal[i]) * (filtered - ideal[i]); |
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}
ff_timefilter_destroy(tf); |
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if (error < best_error) {
best_error = error;
bestpar0 = par0;
bestpar1 = par1;
better = 1; |
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}
}
} |
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} while (better); |
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#if 0 |
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double lastfil = 9;
TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1);
for (i = 0; i < SAMPLES; i++) { |
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double filtered; |
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filtered = ff_timefilter_update(tf, samples[i], 1);
printf("%f %f %f %f\n", i - samples[i] + 10, filtered - samples[i],
samples[FFMAX(i, 1)] - samples[FFMAX(i - 1, 0)], filtered - lastfil);
lastfil = filtered; |
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}
ff_timefilter_destroy(tf);
#else |
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printf(" [%f %f %9f]", bestpar0, bestpar1, best_error); |
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#endif |
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}
printf("\n");
} |
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return 0; |
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}
#endif |