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timefilter.c
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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 FFmpeg.
9  *
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.
14  *
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.
19  *
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
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 /* 1 - exp(-x) using a 3-order power series */
41 static double qexpneg(double x)
42 {
43  return 1 - 1 / (1 + x * (1 + x / 2 * (1 + x / 3)));
44 }
45 
46 TimeFilter *ff_timefilter_new(double time_base,
47  double period,
48  double bandwidth)
49 {
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;
55  return self;
56 }
57 
59 {
60  av_freep(&self);
61 }
62 
64 {
65  self->count = 0;
66 }
67 
68 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
69 {
70  self->count++;
71  if (self->count == 1) {
72  self->cycle_time = system_time;
73  } else {
74  double loop_error;
75  self->cycle_time += self->clock_period * period;
76  loop_error = system_time - self->cycle_time;
77 
78  self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
79  self->clock_period += self->feedback3_factor * loop_error;
80  }
81  return self->cycle_time;
82 }
83 
84 double ff_timefilter_eval(TimeFilter *self, double delta)
85 {
86  return self->cycle_time + self->clock_period * delta;
87 }
88 
89 #ifdef TEST
90 #include "libavutil/lfg.h"
91 #define LFG_MAX ((1LL << 32) - 1)
92 
93 int main(void)
94 {
95  AVLFG prng;
96  double n0, n1;
97 #define SAMPLES 1000
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;
104  double bestpar0 = 1;
105  double bestpar1 = 1;
106  int better, i;
107 
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;
115  }
116 
117  do {
118  double par0, par1;
119  better = 0;
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) {
122  double error = 0;
123  TimeFilter *tf = ff_timefilter_new(1, par0, par1);
124  for (i = 0; i < SAMPLES; i++) {
125  double filtered;
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]);
130  }
132  if (error < best_error) {
133  best_error = error;
134  bestpar0 = par0;
135  bestpar1 = par1;
136  better = 1;
137  }
138  }
139  }
140  } while (better);
141 #if 0
142  double lastfil = 9;
143  TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1);
144  for (i = 0; i < SAMPLES; i++) {
145  double filtered;
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);
149  lastfil = filtered;
150  }
152 #else
153  printf(" [%f %f %9f]", bestpar0, bestpar1, best_error);
154 #endif
155  }
156  printf("\n");
157  }
158  return 0;
159 }
160 #endif