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