blob: cb3d0a788f5a661afd1519c295c4d290586c9901
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 */ |
111 |