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/*
* Delay Locked Loop based time filter
* Copyright (c) 2009 Samalyse
* Copyright (c) 2009 Michael Niedermayer
* Author: Olivier Guilyardi <olivier samalyse com>
* Michael Niedermayer <michaelni gmx at>
*
* 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
*/
#include "libavutil/common.h"
#include "libavutil/mem.h"
#include "timefilter.h"
struct TimeFilter {
// Delay Locked Loop data. These variables refer to mathematical
// concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf
double cycle_time;
double feedback2_factor;
double feedback3_factor;
double clock_period;
int count;
};
/* 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)
{
TimeFilter *self = av_mallocz(sizeof(TimeFilter));
double o = 2 * M_PI * bandwidth * period * time_base;
if (!self)
return NULL;
self->clock_period = time_base;
self->feedback2_factor = qexpneg(M_SQRT2 * o);
self->feedback3_factor = qexpneg(o * o) / period;
return self;
}
void ff_timefilter_destroy(TimeFilter *self)
{
av_freep(&self);
}
void ff_timefilter_reset(TimeFilter *self)
{
self->count = 0;
}
double ff_timefilter_update(TimeFilter *self, double system_time, double period)
{
self->count++;
if (self->count == 1) {
self->cycle_time = system_time;
} else {
double loop_error;
self->cycle_time += self->clock_period * period;
loop_error = system_time - self->cycle_time;
self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
self->clock_period += self->feedback3_factor * loop_error;
}
return self->cycle_time;
}
double ff_timefilter_eval(TimeFilter *self, double delta)
{
return self->cycle_time + self->clock_period * delta;
}
#ifdef TEST
#include "libavutil/lfg.h"
#define LFG_MAX ((1LL << 32) - 1)
int main(void)
{
AVLFG prng;
double n0, n1;
#define SAMPLES 1000
double ideal[SAMPLES];
double samples[SAMPLES];
double samplet[SAMPLES];
for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) {
for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) {
double best_error = 1000000000;
double bestpar0 = n0 ? 1 : 100000;
double bestpar1 = 1;
int better, i;
av_lfg_init(&prng, 123);
for (i = 0; i < SAMPLES; i++) {
samplet[i] = 10 + i + (av_lfg_get(&prng) < LFG_MAX/2 ? 0 : 0.999);
ideal[i] = samplet[i] + n1 * i / (1000);
samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2) / (LFG_MAX * 10LL);
if(i && samples[i]<samples[i-1])
samples[i]=samples[i-1]+0.001;
}
do {
double par0, par1;
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);
if (!tf) {
printf("Could not allocate memory for timefilter.\n");
exit(1);
}
for (i = 0; i < SAMPLES; i++) {
double filtered;
filtered = ff_timefilter_update(tf, samples[i], i ? (samplet[i] - samplet[i-1]) : 1);
if(filtered < 0 || filtered > 1000000000)
printf("filter is unstable\n");
error += (filtered - ideal[i]) * (filtered - ideal[i]);
}
ff_timefilter_destroy(tf);
if (error < best_error) {
best_error = error;
bestpar0 = par0;
bestpar1 = par1;
better = 1;
}
}
}
} while (better);
#if 0
double lastfil = 9;
TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1);
for (i = 0; i < SAMPLES; i++) {
double filtered;
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;
}
ff_timefilter_destroy(tf);
#else
printf(" [%12f %11f %9f]", bestpar0, bestpar1, best_error);
#endif
}
printf("\n");
}
return 0;
}
#endif
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