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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 <math.h>
#include <stddef.h>
#include "libavutil/macros.h"
#include "libavutil/mathematics.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;
}
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