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 <math.h>
26 #include <stddef.h>
27
28 #include "libavutil/macros.h"
29 #include "libavutil/mathematics.h"
30 #include "libavutil/mem.h"
31
32 #include "timefilter.h"
33
34 struct TimeFilter {
35 // Delay Locked Loop data. These variables refer to mathematical
36 // concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf
37 double cycle_time;
38 double feedback2_factor;
39 double feedback3_factor;
40 double clock_period;
41 int count;
42 };
43
44 /* 1 - exp(-x) using a 3-order power series */
qexpneg(double x)45 static double qexpneg(double x)
46 {
47 return 1 - 1 / (1 + x * (1 + x / 2 * (1 + x / 3)));
48 }
49
ff_timefilter_new(double time_base, double period, double bandwidth)50 TimeFilter *ff_timefilter_new(double time_base,
51 double period,
52 double bandwidth)
53 {
54 TimeFilter *self = av_mallocz(sizeof(TimeFilter));
55 double o = 2 * M_PI * bandwidth * period * time_base;
56
57 if (!self)
58 return NULL;
59
60 self->clock_period = time_base;
61 self->feedback2_factor = qexpneg(M_SQRT2 * o);
62 self->feedback3_factor = qexpneg(o * o) / period;
63 return self;
64 }
65
ff_timefilter_destroy(TimeFilter *self)66 void ff_timefilter_destroy(TimeFilter *self)
67 {
68 av_freep(&self);
69 }
70
ff_timefilter_reset(TimeFilter *self)71 void ff_timefilter_reset(TimeFilter *self)
72 {
73 self->count = 0;
74 }
75
ff_timefilter_update(TimeFilter *self, double system_time, double period)76 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
77 {
78 self->count++;
79 if (self->count == 1) {
80 self->cycle_time = system_time;
81 } else {
82 double loop_error;
83 self->cycle_time += self->clock_period * period;
84 loop_error = system_time - self->cycle_time;
85
86 self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
87 self->clock_period += self->feedback3_factor * loop_error;
88 }
89 return self->cycle_time;
90 }
91
ff_timefilter_eval(TimeFilter *self, double delta)92 double ff_timefilter_eval(TimeFilter *self, double delta)
93 {
94 return self->cycle_time + self->clock_period * delta;
95 }
96