FFmpeg
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 
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 
53  if (!self)
54  return NULL;
55 
56  self->clock_period = time_base;
57  self->feedback2_factor = qexpneg(M_SQRT2 * o);
58  self->feedback3_factor = qexpneg(o * o) / period;
59  return self;
60 }
61 
63 {
64  av_freep(&self);
65 }
66 
68 {
69  self->count = 0;
70 }
71 
72 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
73 {
74  self->count++;
75  if (self->count == 1) {
76  self->cycle_time = system_time;
77  } else {
78  double loop_error;
79  self->cycle_time += self->clock_period * period;
80  loop_error = system_time - self->cycle_time;
81 
82  self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
83  self->clock_period += self->feedback3_factor * loop_error;
84  }
85  return self->cycle_time;
86 }
87 
88 double ff_timefilter_eval(TimeFilter *self, double delta)
89 {
90  return self->cycle_time + self->clock_period * delta;
91 }
#define NULL
Definition: coverity.c:32
void ff_timefilter_destroy(TimeFilter *self)
Free all resources associated with the filter.
Definition: timefilter.c:62
Memory handling functions.
void ff_timefilter_reset(TimeFilter *self)
Reset the filter.
Definition: timefilter.c:67
void * av_mallocz(size_t size)
Allocate a memory block with alignment suitable for all memory accesses (including vectors if availab...
Definition: mem.c:236
double ff_timefilter_eval(TimeFilter *self, double delta)
Evaluate the filter at a specified time.
Definition: timefilter.c:88
double cycle_time
Definition: timefilter.c:33
Opaque type representing a time filter state.
Definition: timefilter.c:30
float delta
double clock_period
Definition: timefilter.c:36
static double qexpneg(double x)
Definition: timefilter.c:41
#define FFMAX(a, b)
Definition: common.h:94
it s the only field you need to keep assuming you have a context There is some magic you don t need to care about around this just let it vf default minimum maximum flags name is the option keep it simple and lowercase description are in without period
double feedback3_factor
Definition: timefilter.c:35
TimeFilter * ff_timefilter_new(double time_base, double period, double bandwidth)
Create a new Delay Locked Loop time filter.
Definition: timefilter.c:46
#define M_SQRT2
Definition: mathematics.h:61
double ff_timefilter_update(TimeFilter *self, double system_time, double period)
Update the filter.
Definition: timefilter.c:72
common internal and external API header
double feedback2_factor
Definition: timefilter.c:34
#define av_freep(p)
#define M_PI
Definition: mathematics.h:52