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
|
/*
* Delay Locked Loop based time filter prototypes and declarations
* Copyright (c) 2009 Samalyse
* Author: Olivier Guilyardi <olivier samalyse com>
*
* 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
*/
#ifndef AVFORMAT_TIMEFILTER_H
#define AVFORMAT_TIMEFILTER_H
/**
* Opaque type representing a time filter state
*
* The purpose of this filter is to provide a way to compute accurate time
* stamps that can be compared to wall clock time, especially when dealing
* with two clocks: the system clock and a hardware device clock, such as
* a soundcard.
*/
typedef struct TimeFilter TimeFilter;
/**
* Create a new Delay Locked Loop time filter
*
* feedback2_factor and feedback3_factor are the factors used for the
* multiplications that are respectively performed in the second and third
* feedback paths of the loop.
*
* Unless you know what you are doing, you should set these as follow:
*
* o = 2 * M_PI * bandwidth * period
* feedback2_factor = sqrt(2 * o)
* feedback3_factor = o * o
*
* Where bandwidth is up to you to choose. Smaller values will filter out more
* of the jitter, but also take a longer time for the loop to settle. A good
* starting point is something between 0.3 and 3 Hz.
*
* For more details about these parameters and background concepts please see:
* http://www.kokkinizita.net/papers/usingdll.pdf
*/
TimeFilter * ff_timefilter_new(double feedback2_factor, double feedback3_factor);
/**
* Update the filter
*
* This function must be called in real time, at each process cycle.
*
* period is the device cycle duration in seconds. For example, at
* 44.1Hz and a buffer size of 512 frames, period = 512 / 44100.
*
* system_time, in seconds, should be the value of the system clock time,
* at (or as close as possible to) the moment the device hardware interrupt
* occured (or any other event the device clock raises at the beginning of a
* cycle).
*
* @return the filtered time, in seconds
*/
double ff_timefilter_update(TimeFilter *self, double system_time, double period);
/**
* Reset the filter
*
* This function should mainly be called in case of XRUN.
*
* Warning: after calling this, the filter is in an undetermined state until
* the next call to ff_timefilter_update()
*/
void ff_timefilter_reset(TimeFilter *);
/**
* Free all resources associated with the filter
*/
void ff_timefilter_destroy(TimeFilter *);
#endif /* AVFORMAT_TIMEFILTER_H */
|
