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143 lines
4.7 KiB
C
143 lines
4.7 KiB
C
/*
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* Delay Locked Loop based time filter
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* 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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*
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* This file is part of Libav.
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*
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* Libav is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* Libav is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with Libav; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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#include "libavutil/common.h"
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#include "libavutil/mem.h"
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#include "config.h"
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#include "timefilter.h"
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struct TimeFilter {
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// Delay Locked Loop data. These variables refer to mathematical
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// concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf
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double cycle_time;
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double feedback2_factor;
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double feedback3_factor;
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double clock_period;
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int count;
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};
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TimeFilter *ff_timefilter_new(double clock_period,
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double feedback2_factor,
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double feedback3_factor)
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{
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TimeFilter *self = av_mallocz(sizeof(TimeFilter));
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self->clock_period = clock_period;
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self->feedback2_factor = feedback2_factor;
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self->feedback3_factor = feedback3_factor;
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return self;
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}
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void ff_timefilter_destroy(TimeFilter *self)
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{
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av_freep(&self);
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}
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void ff_timefilter_reset(TimeFilter *self)
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{
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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) {
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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;
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loop_error = system_time - self->cycle_time;
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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 / period;
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}
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return self->cycle_time;
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}
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#ifdef TEST
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#include "libavutil/lfg.h"
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#define LFG_MAX ((1LL << 32) - 1)
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int main(void)
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{
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AVLFG prng;
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double n0, n1;
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#define SAMPLES 1000
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double ideal[SAMPLES];
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double samples[SAMPLES];
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for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) {
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for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) {
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double best_error = 1000000000;
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double bestpar0 = 1;
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double bestpar1 = 0.001;
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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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ideal[i] = 10 + 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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}
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do {
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double par0, par1;
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better = 0;
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for (par0 = bestpar0 * 0.8; par0 <= bestpar0 * 1.21; par0 += bestpar0 * 0.05) {
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for (par1 = bestpar1 * 0.8; par1 <= bestpar1 * 1.21; par1 += bestpar1 * 0.05) {
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double error = 0;
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TimeFilter *tf = ff_timefilter_new(1, par0, par1);
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for (i = 0; i < SAMPLES; i++) {
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double filtered;
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filtered = ff_timefilter_update(tf, samples[i], 1);
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error += (filtered - ideal[i]) * (filtered - ideal[i]);
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}
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ff_timefilter_destroy(tf);
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if (error < best_error) {
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best_error = error;
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bestpar0 = par0;
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bestpar1 = par1;
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better = 1;
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}
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}
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}
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} while (better);
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#if 0
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double lastfil = 9;
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TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1);
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for (i = 0; i < SAMPLES; i++) {
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double filtered;
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filtered = ff_timefilter_update(tf, samples[i], 1);
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printf("%f %f %f %f\n", i - samples[i] + 10, filtered - samples[i],
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samples[FFMAX(i, 1)] - samples[FFMAX(i - 1, 0)], filtered - lastfil);
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lastfil = filtered;
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}
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ff_timefilter_destroy(tf);
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#else
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printf(" [%f %f %9f]", bestpar0, bestpar1, best_error);
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#endif
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}
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printf("\n");
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}
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return 0;
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}
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#endif
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