libavformat/timefilter.h

   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 AVFORMAT_TIMEFILTER_H
  26 #define AVFORMAT_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
  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 clock_period period of the hardware clock in seconds
  57  *        (for example 1.0/44100)
  58  *
  59  * For more details about these parameters and background concepts please see:
  60  * http://www.kokkinizita.net/papers/usingdll.pdf
  61  */
  62 TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor);
  63
  64 /**
  65  * Update the filter
  66  *
  67  * This function must be called in real time, at each process cycle.
  68  *
  69  * @param period the device cycle duration in clock_periods. For example, at
  70  * 44.1kHz and a buffer size of 512 frames, period = 512 when clock_period
  71  * was 1.0/44100, or 512/44100 if clock_period was 1.
  72  *
  73  * system_time, in seconds, should be the value of the system clock time,
  74  * at (or as close as possible to) the moment the device hardware interrupt
  75  * occured (or any other event the device clock raises at the beginning of a
  76  * cycle).
  77  *
  78  * @return the filtered time, in seconds
  79  */
  80 double ff_timefilter_update(TimeFilter *self, double system_time, double period);
  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 /* AVFORMAT_TIMEFILTER_H */