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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 | * 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_in_seconds | |
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 time_base period of the hardware clock in seconds | |
57 | * (for example 1.0/44100) | |
58 | * @param period expected update interval, in input units | |
59 | * @param brandwidth filtering bandwidth, in Hz | |
60 | * | |
61 | * @return a pointer to a TimeFilter struct, or NULL on error | |
62 | * | |
63 | * For more details about these parameters and background concepts please see: | |
64 | * http://www.kokkinizita.net/papers/usingdll.pdf | |
65 | */ | |
66 | TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor); | |
67 | ||
68 | /** | |
69 | * Update the filter | |
70 | * | |
71 | * This function must be called in real time, at each process cycle. | |
72 | * | |
73 | * @param period the device cycle duration in clock_periods. For example, at | |
74 | * 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period | |
75 | * was 1.0/44100, or 512/44100 if clock_period was 1. | |
76 | * | |
77 | * system_time, in seconds, should be the value of the system clock time, | |
78 | * at (or as close as possible to) the moment the device hardware interrupt | |
79 | * occurred (or any other event the device clock raises at the beginning of a | |
80 | * cycle). | |
81 | * | |
82 | * @return the filtered time, in seconds | |
83 | */ | |
84 | double ff_timefilter_update(TimeFilter *self, double system_time, double period); | |
85 | ||
86 | /** | |
87 | * Evaluate the filter at a specified time | |
88 | * | |
89 | * @param delta difference between the requested time and the current time | |
90 | * (last call to ff_timefilter_update). | |
91 | * @return the filtered time | |
92 | */ | |
93 | double ff_timefilter_eval(TimeFilter *self, double delta); | |
94 | ||
95 | /** | |
96 | * Reset the filter | |
97 | * | |
98 | * This function should mainly be called in case of XRUN. | |
99 | * | |
100 | * Warning: after calling this, the filter is in an undetermined state until | |
101 | * the next call to ff_timefilter_update() | |
102 | */ | |
103 | void ff_timefilter_reset(TimeFilter *); | |
104 | ||
105 | /** | |
106 | * Free all resources associated with the filter | |
107 | */ | |
108 | void ff_timefilter_destroy(TimeFilter *); | |
109 | ||
110 | #endif /* AVDEVICE_TIMEFILTER_H */ |