/* * 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 "config.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