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 */ 36 typedef struct TimeFilter TimeFilter; 37 38 39 /** 40 * Create a new Delay Locked Loop time filter 41 * 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. 45 * 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 50 * 51 * @return a pointer to a TimeFilter struct, or NULL on error 52 */ 53 TimeFilter * ff_timefilter_new(double time_base, double period, double bandwidth); 54 55 /** 56 * Update the filter 57 * 58 * This function must be called in real time, at each process cycle. 59 * 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. 63 * 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 67 * cycle). 68 * 69 * @return the filtered time, in seconds 70 */ 71 double ff_timefilter_update(TimeFilter *self, double system_time, double period); 72 73 /** 74 * Evaluate the filter at a specified time 75 * 76 * @param delta difference between the requested time and the current time 77 * (last call to ff_timefilter_update). 78 * @return the filtered time 79 */ 80 double ff_timefilter_eval(TimeFilter *self, double delta); 81 82 /** 83 * Reset the filter 84 * 85 * This function should mainly be called in case of XRUN. 86 * 87 * Warning: after calling this, the filter is in an undetermined state until 88 * the next call to ff_timefilter_update() 89 */ 90 void ff_timefilter_reset(TimeFilter *); 91 92 /** 93 * Free all resources associated with the filter 94 */ 95 void ff_timefilter_destroy(TimeFilter *); 96 97 #endif /* AVDEVICE_TIMEFILTER_H */ 98