timefilter.c
Go to the documentation of this file.
1 /*
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>
7  *
8  * This file is part of Libav.
9  *
10  * Libav 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.
14  *
15  * Libav 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.
19  *
20  * You should have received a copy of the GNU Lesser General Public
21  * License along with Libav; if not, write to the Free Software
22  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
23  */
24 
25 #include "libavutil/common.h"
26 #include "libavutil/mem.h"
27 #include "config.h"
28 #include "timefilter.h"
29 
30 struct TimeFilter {
31  // Delay Locked Loop data. These variables refer to mathematical
32  // concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf
33  double cycle_time;
36  double clock_period;
37  int count;
38 };
39 
40 TimeFilter *ff_timefilter_new(double clock_period,
41  double feedback2_factor,
42  double feedback3_factor)
43 {
44  TimeFilter *self = av_mallocz(sizeof(TimeFilter));
45  self->clock_period = clock_period;
46  self->feedback2_factor = feedback2_factor;
47  self->feedback3_factor = feedback3_factor;
48  return self;
49 }
50 
52 {
53  av_freep(&self);
54 }
55 
57 {
58  self->count = 0;
59 }
60 
61 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
62 {
63  self->count++;
64  if (self->count == 1) {
65  self->cycle_time = system_time;
66  } else {
67  double loop_error;
68  self->cycle_time += self->clock_period * period;
69  loop_error = system_time - self->cycle_time;
70 
71  self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
72  self->clock_period += self->feedback3_factor * loop_error / period;
73  }
74  return self->cycle_time;
75 }
76 
77 #ifdef TEST
78 #include "libavutil/lfg.h"
79 #define LFG_MAX ((1LL << 32) - 1)
80 
81 int main(void)
82 {
83  AVLFG prng;
84  double n0, n1;
85 #define SAMPLES 1000
86  double ideal[SAMPLES];
87  double samples[SAMPLES];
88  for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) {
89  for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) {
90  double best_error = 1000000000;
91  double bestpar0 = 1;
92  double bestpar1 = 0.001;
93  int better, i;
94 
95  av_lfg_init(&prng, 123);
96  for (i = 0; i < SAMPLES; i++) {
97  ideal[i] = 10 + i + n1 * i / (1000);
98  samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2) / (LFG_MAX * 10LL);
99  }
100 
101  do {
102  double par0, par1;
103  better = 0;
104  for (par0 = bestpar0 * 0.8; par0 <= bestpar0 * 1.21; par0 += bestpar0 * 0.05) {
105  for (par1 = bestpar1 * 0.8; par1 <= bestpar1 * 1.21; par1 += bestpar1 * 0.05) {
106  double error = 0;
107  TimeFilter *tf = ff_timefilter_new(1, par0, par1);
108  for (i = 0; i < SAMPLES; i++) {
109  double filtered;
110  filtered = ff_timefilter_update(tf, samples[i], 1);
111  error += (filtered - ideal[i]) * (filtered - ideal[i]);
112  }
114  if (error < best_error) {
115  best_error = error;
116  bestpar0 = par0;
117  bestpar1 = par1;
118  better = 1;
119  }
120  }
121  }
122  } while (better);
123 #if 0
124  double lastfil = 9;
125  TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1);
126  for (i = 0; i < SAMPLES; i++) {
127  double filtered;
128  filtered = ff_timefilter_update(tf, samples[i], 1);
129  printf("%f %f %f %f\n", i - samples[i] + 10, filtered - samples[i],
130  samples[FFMAX(i, 1)] - samples[FFMAX(i - 1, 0)], filtered - lastfil);
131  lastfil = filtered;
132  }
134 #else
135  printf(" [%f %f %9f]", bestpar0, bestpar1, best_error);
136 #endif
137  }
138  printf("\n");
139  }
140  return 0;
141 }
142 #endif