Libav
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 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 
41  double feedback2_factor,
42  double feedback3_factor)
43 {
44  TimeFilter *self = av_mallocz(sizeof(TimeFilter));
45 
46  if (!self)
47  return NULL;
48 
49  self->clock_period = clock_period;
50  self->feedback2_factor = feedback2_factor;
51  self->feedback3_factor = feedback3_factor;
52  return self;
53 }
54 
56 {
57  av_freep(&self);
58 }
59 
61 {
62  self->count = 0;
63 }
64 
65 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
66 {
67  self->count++;
68  if (self->count == 1) {
69  self->cycle_time = system_time;
70  } else {
71  double loop_error;
72  self->cycle_time += self->clock_period * period;
73  loop_error = system_time - self->cycle_time;
74 
75  self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
76  self->clock_period += self->feedback3_factor * loop_error / period;
77  }
78  return self->cycle_time;
79 }
80 
81 #ifdef TEST
82 #include "libavutil/lfg.h"
83 #define LFG_MAX ((1LL << 32) - 1)
84 
85 int main(void)
86 {
87  AVLFG prng;
88  double n0, n1;
89 #define SAMPLES 1000
90  double ideal[SAMPLES];
91  double samples[SAMPLES];
92  for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) {
93  for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) {
94  double best_error = 1000000000;
95  double bestpar0 = 1;
96  double bestpar1 = 0.001;
97  int better, i;
98 
99  av_lfg_init(&prng, 123);
100  for (i = 0; i < SAMPLES; i++) {
101  ideal[i] = 10 + i + n1 * i / (1000);
102  samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2) / (LFG_MAX * 10LL);
103  }
104 
105  do {
106  double par0, par1;
107  better = 0;
108  for (par0 = bestpar0 * 0.8; par0 <= bestpar0 * 1.21; par0 += bestpar0 * 0.05) {
109  for (par1 = bestpar1 * 0.8; par1 <= bestpar1 * 1.21; par1 += bestpar1 * 0.05) {
110  double error = 0;
111  TimeFilter *tf = ff_timefilter_new(1, par0, par1);
112  if (!tf) {
113  printf("Could not allocate memory for timefilter.\n");
114  exit(1);
115  }
116  for (i = 0; i < SAMPLES; i++) {
117  double filtered;
118  filtered = ff_timefilter_update(tf, samples[i], 1);
119  error += (filtered - ideal[i]) * (filtered - ideal[i]);
120  }
122  if (error < best_error) {
123  best_error = error;
124  bestpar0 = par0;
125  bestpar1 = par1;
126  better = 1;
127  }
128  }
129  }
130  } while (better);
131 #if 0
132  double lastfil = 9;
133  TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1);
134  for (i = 0; i < SAMPLES; i++) {
135  double filtered;
136  filtered = ff_timefilter_update(tf, samples[i], 1);
137  printf("%f %f %f %f\n", i - samples[i] + 10, filtered - samples[i],
138  samples[FFMAX(i, 1)] - samples[FFMAX(i - 1, 0)], filtered - lastfil);
139  lastfil = filtered;
140  }
142 #else
143  printf(" [%f %f %9f]", bestpar0, bestpar1, best_error);
144 #endif
145  }
146  printf("\n");
147  }
148  return 0;
149 }
150 #endif
Definition: lfg.h:25
void ff_timefilter_destroy(TimeFilter *self)
Free all resources associated with the filter.
Definition: timefilter.c:55
memory handling functions
void ff_timefilter_reset(TimeFilter *self)
Reset the filter.
Definition: timefilter.c:60
double cycle_time
Definition: timefilter.c:33
void av_freep(void *arg)
Free a memory block which has been allocated with av_malloc(z)() or av_realloc() and set the pointer ...
Definition: mem.c:198
Opaque type representing a time filter state.
Definition: timefilter.c:30
double clock_period
Definition: timefilter.c:36
int main(int argc, char **argv)
Definition: avconv.c:2609
#define FFMAX(a, b)
Definition: common.h:55
double feedback3_factor
Definition: timefilter.c:35
NULL
Definition: eval.c:55
static unsigned int av_lfg_get(AVLFG *c)
Get the next random unsigned 32-bit number using an ALFG.
Definition: lfg.h:38
TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor)
Create a new Delay Locked Loop time filter.
Definition: timefilter.c:40
av_cold void av_lfg_init(AVLFG *c, unsigned int seed)
Definition: lfg.c:30
double ff_timefilter_update(TimeFilter *self, double system_time, double period)
Update the filter.
Definition: timefilter.c:65
common internal and external API header
double feedback2_factor
Definition: timefilter.c:34
void * av_mallocz(size_t size)
Allocate a block of size bytes with alignment suitable for all memory accesses (including vectors if ...
Definition: mem.c:205