2 * Delay Locked Loop based time filter
3 * Copyright (c) 2009 Samalyse
4 * Copyright (c) 2009 Michael Niedermayer
5 * Author: Olivier Guilyardi <olivier samalyse com>
6 * Michael Niedermayer <michaelni gmx at>
8 * This file is part of FFmpeg.
10 * FFmpeg is free software; you can redistribute it and/or
11 * modify it under the terms of the GNU Lesser General Public
12 * License as published by the Free Software Foundation; either
13 * version 2.1 of the License, or (at your option) any later version.
15 * FFmpeg is distributed in the hope that it will be useful,
16 * but WITHOUT ANY WARRANTY; without even the implied warranty of
17 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 * Lesser General Public License for more details.
20 * You should have received a copy of the GNU Lesser General Public
21 * License along with FFmpeg; if not, write to the Free Software
22 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
25 #include "libavutil/common.h"
26 #include "libavutil/mem.h"
28 #include "timefilter.h"
31 // Delay Locked Loop data. These variables refer to mathematical
32 // concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf
34 double feedback2_factor;
35 double feedback3_factor;
40 /* 1 - exp(-x) using a 3-order power series */
41 static double qexpneg(double x)
43 return 1 - 1 / (1 + x * (1 + x / 2 * (1 + x / 3)));
46 TimeFilter *ff_timefilter_new(double time_base,
50 TimeFilter *self = av_mallocz(sizeof(TimeFilter));
51 double o = 2 * M_PI * bandwidth * period * time_base;
52 self->clock_period = time_base;
53 self->feedback2_factor = qexpneg(M_SQRT2 * o);
54 self->feedback3_factor = qexpneg(o * o) / period;
58 void ff_timefilter_destroy(TimeFilter *self)
63 void ff_timefilter_reset(TimeFilter *self)
68 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
71 if (self->count == 1) {
72 self->cycle_time = system_time;
75 self->cycle_time += self->clock_period * period;
76 loop_error = system_time - self->cycle_time;
78 self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
79 self->clock_period += self->feedback3_factor * loop_error;
81 return self->cycle_time;
84 double ff_timefilter_eval(TimeFilter *self, double delta)
86 return self->cycle_time + self->clock_period * delta;
90 #include "libavutil/lfg.h"
91 #define LFG_MAX ((1LL << 32) - 1)
98 double ideal[SAMPLES];
99 double samples[SAMPLES];
100 double samplet[SAMPLES];
101 for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) {
102 for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) {
103 double best_error = 1000000000;
108 av_lfg_init(&prng, 123);
109 for (i = 0; i < SAMPLES; i++) {
110 samplet[i] = 10 + i + (av_lfg_get(&prng) < LFG_MAX/2 ? 0 : 0.999);
111 ideal[i] = samplet[i] + n1 * i / (1000);
112 samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2) / (LFG_MAX * 10LL);
113 if(i && samples[i]<samples[i-1])
114 samples[i]=samples[i-1]+0.001;
120 for (par0 = bestpar0 * 0.8; par0 <= bestpar0 * 1.21; par0 += bestpar0 * 0.05) {
121 for (par1 = bestpar1 * 0.8; par1 <= bestpar1 * 1.21; par1 += bestpar1 * 0.05) {
123 TimeFilter *tf = ff_timefilter_new(1, par0, par1);
124 for (i = 0; i < SAMPLES; i++) {
126 filtered = ff_timefilter_update(tf, samples[i], i ? (samplet[i] - samplet[i-1]) : 1);
127 if(filtered < 0 || filtered > 1000000000)
128 printf("filter is unstable\n");
129 error += (filtered - ideal[i]) * (filtered - ideal[i]);
131 ff_timefilter_destroy(tf);
132 if (error < best_error) {
143 TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1);
144 for (i = 0; i < SAMPLES; i++) {
146 filtered = ff_timefilter_update(tf, samples[i], 1);
147 printf("%f %f %f %f\n", i - samples[i] + 10, filtered - samples[i],
148 samples[FFMAX(i, 1)] - samples[FFMAX(i - 1, 0)], filtered - lastfil);
151 ff_timefilter_destroy(tf);
153 printf(" [%f %f %9f]", bestpar0, bestpar1, best_error);