FFmpeg
timefilter.c
Go to the documentation of this file.
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;
40  double clock_period;
41  int count;
42 };
43 
44 /* 1 - exp(-x) using a 3-order power series */
45 static double qexpneg(double x)
46 {
47  return 1 - 1 / (1 + x * (1 + x / 2 * (1 + x / 3)));
48 }
49 
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 
67 {
68  av_freep(&self);
69 }
70 
72 {
73  self->count = 0;
74 }
75 
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 
92 double ff_timefilter_eval(TimeFilter *self, double delta)
93 {
94  return self->cycle_time + self->clock_period * delta;
95 }
TimeFilter
Opaque type representing a time filter state.
Definition: timefilter.c:34
mathematics.h
FFMAX
#define FFMAX(a, b)
Definition: macros.h:47
TimeFilter::cycle_time
double cycle_time
Definition: timefilter.c:37
ff_timefilter_eval
double ff_timefilter_eval(TimeFilter *self, double delta)
Evaluate the filter at a specified time.
Definition: timefilter.c:92
macros.h
ff_timefilter_new
TimeFilter * ff_timefilter_new(double time_base, double period, double bandwidth)
Create a new Delay Locked Loop time filter.
Definition: timefilter.c:50
TimeFilter::count
int count
Definition: timefilter.c:41
TimeFilter::clock_period
double clock_period
Definition: timefilter.c:40
NULL
#define NULL
Definition: coverity.c:32
timefilter.h
period
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
Definition: writing_filters.txt:89
ff_timefilter_reset
void ff_timefilter_reset(TimeFilter *self)
Reset the filter.
Definition: timefilter.c:71
M_PI
#define M_PI
Definition: mathematics.h:52
TimeFilter::feedback3_factor
double feedback3_factor
Definition: timefilter.c:39
ff_timefilter_destroy
void ff_timefilter_destroy(TimeFilter *self)
Free all resources associated with the filter.
Definition: timefilter.c:66
delta
float delta
Definition: vorbis_enc_data.h:430
av_mallocz
void * av_mallocz(size_t size)
Allocate a memory block with alignment suitable for all memory accesses (including vectors if availab...
Definition: mem.c:254
ff_timefilter_update
double ff_timefilter_update(TimeFilter *self, double system_time, double period)
Update the filter.
Definition: timefilter.c:76
qexpneg
static double qexpneg(double x)
Definition: timefilter.c:45
mem.h
M_SQRT2
#define M_SQRT2
Definition: mathematics.h:61
TimeFilter::feedback2_factor
double feedback2_factor
Definition: timefilter.c:38
av_freep
#define av_freep(p)
Definition: tableprint_vlc.h:34