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/*
* Delay Locked Loop based time filter prototypes and declarations
* Copyright (c) 2009 Samalyse
* Copyright (c) 2009 Michael Niedermayer
* Author: Olivier Guilyardi <olivier samalyse com>
* Michael Niedermayer <michaelni gmx at>
*
* This file is part of Libav.
*
* Libav is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* Libav is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with Libav; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef AVDEVICE_TIMEFILTER_H
#define AVDEVICE_TIMEFILTER_H
/**
* Opaque type representing a time filter state
*
* The purpose of this filter is to provide a way to compute accurate time
* stamps that can be compared to wall clock time, especially when dealing
* with two clocks: the system clock and a hardware device clock, such as
* a soundcard.
*/
typedef struct TimeFilter TimeFilter;
/**
* Create a new Delay Locked Loop time filter
*
* feedback2_factor and feedback3_factor are the factors used for the
* multiplications that are respectively performed in the second and third
* feedback paths of the loop.
*
* Unless you know what you are doing, you should set these as follow:
*
* o = 2 * M_PI * bandwidth * period
* feedback2_factor = sqrt(2 * o)
* feedback3_factor = o * o
*
* Where bandwidth is up to you to choose. Smaller values will filter out more
* of the jitter, but also take a longer time for the loop to settle. A good
* starting point is something between 0.3 and 3 Hz.
*
* @param clock_period period of the hardware clock in seconds
* (for example 1.0/44100)
*
* @return a pointer to a TimeFilter struct, or NULL on error
*
* For more details about these parameters and background concepts please see:
* http://www.kokkinizita.net/papers/usingdll.pdf
*/
TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor);
/**
* Update the filter
*
* This function must be called in real time, at each process cycle.
*
* @param period the device cycle duration in clock_periods. For example, at
* 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period
* was 1.0/44100, or 512/44100 if clock_period was 1.
*
* system_time, in seconds, should be the value of the system clock time,
* at (or as close as possible to) the moment the device hardware interrupt
* occurred (or any other event the device clock raises at the beginning of a
* cycle).
*
* @return the filtered time, in seconds
*/
double ff_timefilter_update(TimeFilter *self, double system_time, double period);
/**
* Reset the filter
*
* This function should mainly be called in case of XRUN.
*
* Warning: after calling this, the filter is in an undetermined state until
* the next call to ff_timefilter_update()
*/
void ff_timefilter_reset(TimeFilter *);
/**
* Free all resources associated with the filter
*/
void ff_timefilter_destroy(TimeFilter *);
#endif /* AVDEVICE_TIMEFILTER_H */
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