1/* 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> 7 * 8 * This file is part of FFmpeg. 9 * 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. 14 * 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. 19 * 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 23 */ 24 25#ifndef AVDEVICE_TIMEFILTER_H 26#define AVDEVICE_TIMEFILTER_H 27 28/** 29 * Opaque type representing a time filter state 30 * 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 34 * a soundcard. 35 */ 36typedef struct TimeFilter TimeFilter; 37 38 39/** 40 * Create a new Delay Locked Loop time filter 41 * 42 * feedback2_factor and feedback3_factor are the factors used for the 43 * multiplications that are respectively performed in the second and third 44 * feedback paths of the loop. 45 * 46 * Unless you know what you are doing, you should set these as follow: 47 * 48 * o = 2 * M_PI * bandwidth * period_in_seconds 49 * feedback2_factor = sqrt(2) * o 50 * feedback3_factor = o * o 51 * 52 * Where bandwidth is up to you to choose. Smaller values will filter out more 53 * of the jitter, but also take a longer time for the loop to settle. A good 54 * starting point is something between 0.3 and 3 Hz. 55 * 56 * @param time_base period of the hardware clock in seconds 57 * (for example 1.0/44100) 58 * @param period expected update interval, in input units 59 * @param brandwidth filtering bandwidth, in Hz 60 * 61 * @return a pointer to a TimeFilter struct, or NULL on error 62 * 63 * For more details about these parameters and background concepts please see: 64 * http://www.kokkinizita.net/papers/usingdll.pdf 65 */ 66TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor); 67 68/** 69 * Update the filter 70 * 71 * This function must be called in real time, at each process cycle. 72 * 73 * @param period the device cycle duration in clock_periods. For example, at 74 * 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period 75 * was 1.0/44100, or 512/44100 if clock_period was 1. 76 * 77 * system_time, in seconds, should be the value of the system clock time, 78 * at (or as close as possible to) the moment the device hardware interrupt 79 * occurred (or any other event the device clock raises at the beginning of a 80 * cycle). 81 * 82 * @return the filtered time, in seconds 83 */ 84double ff_timefilter_update(TimeFilter *self, double system_time, double period); 85 86/** 87 * Evaluate the filter at a specified time 88 * 89 * @param delta difference between the requested time and the current time 90 * (last call to ff_timefilter_update). 91 * @return the filtered time 92 */ 93double ff_timefilter_eval(TimeFilter *self, double delta); 94 95/** 96 * Reset the filter 97 * 98 * This function should mainly be called in case of XRUN. 99 * 100 * Warning: after calling this, the filter is in an undetermined state until 101 * the next call to ff_timefilter_update() 102 */ 103void ff_timefilter_reset(TimeFilter *); 104 105/** 106 * Free all resources associated with the filter 107 */ 108void ff_timefilter_destroy(TimeFilter *); 109 110#endif /* AVDEVICE_TIMEFILTER_H */ 111