h264_metadata: Add option to delete filler data
[libav.git] / libavdevice / timefilter.h
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 Libav.
9 *
10 * Libav 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 * Libav 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 Libav; 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 * feedback2_factor and feedback3_factor are the factors used for the
43 * multiplications that are respectively performed in the second and third
44 * feedback paths of the loop.
45 *
46 * Unless you know what you are doing, you should set these as follow:
47 *
48 * o = 2 * M_PI * bandwidth * period
49 * feedback2_factor = sqrt(2 * o)
50 * feedback3_factor = o * o
51 *
52 * Where bandwidth is up to you to choose. Smaller values will filter out more
53 * of the jitter, but also take a longer time for the loop to settle. A good
54 * starting point is something between 0.3 and 3 Hz.
55 *
56 * @param clock_period period of the hardware clock in seconds
57 * (for example 1.0/44100)
58 *
59 * @return a pointer to a TimeFilter struct, or NULL on error
60 *
61 * For more details about these parameters and background concepts please see:
62 * http://www.kokkinizita.net/papers/usingdll.pdf
63 */
64 TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor);
65
66 /**
67 * Update the filter
68 *
69 * This function must be called in real time, at each process cycle.
70 *
71 * @param period the device cycle duration in clock_periods. For example, at
72 * 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period
73 * was 1.0/44100, or 512/44100 if clock_period was 1.
74 *
75 * system_time, in seconds, should be the value of the system clock time,
76 * at (or as close as possible to) the moment the device hardware interrupt
77 * occurred (or any other event the device clock raises at the beginning of a
78 * cycle).
79 *
80 * @return the filtered time, in seconds
81 */
82 double ff_timefilter_update(TimeFilter *self, double system_time, double period);
83
84 /**
85 * Reset the filter
86 *
87 * This function should mainly be called in case of XRUN.
88 *
89 * Warning: after calling this, the filter is in an undetermined state until
90 * the next call to ff_timefilter_update()
91 */
92 void ff_timefilter_reset(TimeFilter *);
93
94 /**
95 * Free all resources associated with the filter
96 */
97 void ff_timefilter_destroy(TimeFilter *);
98
99 #endif /* AVDEVICE_TIMEFILTER_H */