/* * 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 FFmpeg. * * FFmpeg 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. * * FFmpeg 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 FFmpeg; 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_in_seconds * 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 time_base period of the hardware clock in seconds * (for example 1.0/44100) * @param period expected update interval, in input units * @param brandwidth filtering bandwidth, in Hz * * @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); /** * Evaluate the filter at a specified time * * @param delta difference between the requested time and the current time * (last call to ff_timefilter_update). * @return the filtered time */ double ff_timefilter_eval(TimeFilter *self, double delta); /** * 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 */