2 * Delay Locked Loop based time filter prototypes and declarations
3 * Copyright (c) 2009 Samalyse
4 * Author: Olivier Guilyardi <olivier samalyse com>
6 * This file is part of FFmpeg.
8 * FFmpeg is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
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15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with FFmpeg; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
23 #ifndef AVFORMAT_TIMEFILTER_H
24 #define AVFORMAT_TIMEFILTER_H
27 * Opaque type representing a time filter state
29 * The purpose of this filter is to provide a way to compute accurate time
30 * stamps that can be compared to wall clock time, especially when dealing
31 * with two clocks: the system clock and a hardware device clock, such as
34 typedef struct TimeFilter TimeFilter;
38 * Create a new Delay Locked Loop time filter
40 * feedback2_factor and feedback3_factor are the factors used for the
41 * multiplications that are respectively performed in the second and third
42 * feedback paths of the loop.
44 * Unless you know what you are doing, you should set these as follow:
46 * o = 2 * M_PI * bandwidth * period
47 * feedback2_factor = sqrt(2 * o)
48 * feedback3_factor = o * o
50 * Where bandwidth is up to you to choose. Smaller values will filter out more
51 * of the jitter, but also take a longer time for the loop to settle. A good
52 * starting point is something between 0.3 and 3 Hz.
54 * @param clock_period period of the hardware clock in seconds
55 * (for example 1.0/44100)
57 * For more details about these parameters and background concepts please see:
58 * http://www.kokkinizita.net/papers/usingdll.pdf
60 TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor);
65 * This function must be called in real time, at each process cycle.
67 * @param period the device cycle duration in clock_periods. For example, at
68 * 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period
69 * was 1.0/44100, or 512/44100 if clock_period was 1.
71 * system_time, in seconds, should be the value of the system clock time,
72 * at (or as close as possible to) the moment the device hardware interrupt
73 * occured (or any other event the device clock raises at the beginning of a
76 * @return the filtered time, in seconds
78 double ff_timefilter_update(TimeFilter *self, double system_time, double period);
83 * This function should mainly be called in case of XRUN.
85 * Warning: after calling this, the filter is in an undetermined state until
86 * the next call to ff_timefilter_update()
88 void ff_timefilter_reset(TimeFilter *);
91 * Free all resources associated with the filter
93 void ff_timefilter_destroy(TimeFilter *);
95 #endif /* AVFORMAT_TIMEFILTER_H */