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Diffstat (limited to 'ffmpeg/libavdevice/timefilter.c')
| -rw-r--r-- | ffmpeg/libavdevice/timefilter.c | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/ffmpeg/libavdevice/timefilter.c b/ffmpeg/libavdevice/timefilter.c new file mode 100644 index 0000000..ba2e54e --- /dev/null +++ b/ffmpeg/libavdevice/timefilter.c @@ -0,0 +1,160 @@ +/* + * 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; + 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 = 1; + 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); + 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(" [%f %f %9f]", bestpar0, bestpar1, best_error); +#endif + } + printf("\n"); + } + return 0; +} +#endif |