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>
8 * This file is part of FFmpeg.
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.
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.
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
25 #ifndef AVDEVICE_TIMEFILTER_H
26 #define AVDEVICE_TIMEFILTER_H
29 * Opaque type representing a time filter state
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
36 typedef struct TimeFilter TimeFilter;
40 * Create a new Delay Locked Loop time filter
42 * Where bandwidth is up to you to choose. Smaller values will filter out more
43 * of the jitter, but also take a longer time for the loop to settle. A good
44 * starting point is something between 0.3 and 3 Hz.
46 * @param time_base period of the hardware clock in seconds
47 * (for example 1.0/44100)
48 * @param period expected update interval, in input units
49 * @param brandwidth filtering bandwidth, in Hz
51 * @return a pointer to a TimeFilter struct, or NULL on error
53 TimeFilter * ff_timefilter_new(double time_base, double period, double bandwidth);
58 * This function must be called in real time, at each process cycle.
60 * @param period the device cycle duration in clock_periods. For example, at
61 * 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period
62 * was 1.0/44100, or 512/44100 if clock_period was 1.
64 * system_time, in seconds, should be the value of the system clock time,
65 * at (or as close as possible to) the moment the device hardware interrupt
66 * occurred (or any other event the device clock raises at the beginning of a
69 * @return the filtered time, in seconds
71 double ff_timefilter_update(TimeFilter *self, double system_time, double period);
74 * Evaluate the filter at a specified time
76 * @param delta difference between the requested time and the current time
77 * (last call to ff_timefilter_update).
78 * @return the filtered time
80 double ff_timefilter_eval(TimeFilter *self, double delta);
85 * This function should mainly be called in case of XRUN.
87 * Warning: after calling this, the filter is in an undetermined state until
88 * the next call to ff_timefilter_update()
90 void ff_timefilter_reset(TimeFilter *);
93 * Free all resources associated with the filter
95 void ff_timefilter_destroy(TimeFilter *);
97 #endif /* AVDEVICE_TIMEFILTER_H */