FFmpeg
timefilter.h
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1 /*
2  * Delay Locked Loop based time filter prototypes and declarations
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 #ifndef AVDEVICE_TIMEFILTER_H
26 #define AVDEVICE_TIMEFILTER_H
27 
28 /**
29  * Opaque type representing a time filter state
30  *
31  * The purpose of this filter is to provide a way to compute accurate time
32  * stamps that can be compared to wall clock time, especially when dealing
33  * with two clocks: the system clock and a hardware device clock, such as
34  * a soundcard.
35  */
36 typedef struct TimeFilter TimeFilter;
37 
38 
39 /**
40  * Create a new Delay Locked Loop time filter
41  *
42  * Where bandwidth is up to you to choose. Smaller values will filter out more
43  * of the jitter, but also take a longer time for the loop to settle. A good
44  * starting point is something between 0.3 and 3 Hz.
45  *
46  * @param time_base period of the hardware clock in seconds
47  * (for example 1.0/44100)
48  * @param period expected update interval, in input units
49  * @param brandwidth filtering bandwidth, in Hz
50  *
51  * @return a pointer to a TimeFilter struct, or NULL on error
52  */
53 TimeFilter * ff_timefilter_new(double time_base, double period, double bandwidth);
54 
55 /**
56  * Update the filter
57  *
58  * This function must be called in real time, at each process cycle.
59  *
60  * @param period the device cycle duration in clock_periods. For example, at
61  * 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period
62  * was 1.0/44100, or 512/44100 if clock_period was 1.
63  *
64  * system_time, in seconds, should be the value of the system clock time,
65  * at (or as close as possible to) the moment the device hardware interrupt
66  * occurred (or any other event the device clock raises at the beginning of a
67  * cycle).
68  *
69  * @return the filtered time, in seconds
70  */
71 double ff_timefilter_update(TimeFilter *self, double system_time, double period);
72 
73 /**
74  * Evaluate the filter at a specified time
75  *
76  * @param delta difference between the requested time and the current time
77  * (last call to ff_timefilter_update).
78  * @return the filtered time
79  */
80 double ff_timefilter_eval(TimeFilter *self, double delta);
81 
82 /**
83  * Reset the filter
84  *
85  * This function should mainly be called in case of XRUN.
86  *
87  * Warning: after calling this, the filter is in an undetermined state until
88  * the next call to ff_timefilter_update()
89  */
91 
92 /**
93  * Free all resources associated with the filter
94  */
96 
97 #endif /* AVDEVICE_TIMEFILTER_H */
TimeFilter
Opaque type representing a time filter state.
Definition: timefilter.c:30
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:46
ff_timefilter_update
double ff_timefilter_update(TimeFilter *self, double system_time, double period)
Update the filter.
Definition: timefilter.c:72
ff_timefilter_eval
double ff_timefilter_eval(TimeFilter *self, double delta)
Evaluate the filter at a specified time.
Definition: timefilter.c:88
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_destroy
void ff_timefilter_destroy(TimeFilter *)
Free all resources associated with the filter.
Definition: timefilter.c:62
delta
float delta
Definition: vorbis_enc_data.h:430
ff_timefilter_reset
void ff_timefilter_reset(TimeFilter *)
Reset the filter.
Definition: timefilter.c:67