1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
|
/*
* 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) {
double range = n0 ? 0.8 : 1.0;
for (par1 = bestpar1 * range; par1 <= bestpar1 * (2.01 - range); 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(" [%11f %11f %9f]", bestpar0, bestpar1, best_error);
#endif
}
printf("\n");
}
return 0;
}
#endif
|
