| 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 | * 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 | */ |
| 66 | TimeFilter * 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 | */ |
| 84 | double 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 | */ |
| 93 | double 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 | */ |
| 103 | void ff_timefilter_reset(TimeFilter *); |
| 104 | |
| 105 | /** |
| 106 | * Free all resources associated with the filter |
| 107 | */ |
| 108 | void ff_timefilter_destroy(TimeFilter *); |
| 109 | |
| 110 | #endif /* AVDEVICE_TIMEFILTER_H */ |