2 * Delay Locked Loop based time filter
3 * Copyright (c) 2009 Samalyse
4 * Copyright (c) 2009 Michael Niedermayer
5 * Author: Olivier Guilyardi <olivier samalyse com>
6 * Michael Niedermayer <michaelni gmx at>
8 * This file is part of FFmpeg.
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.
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.
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
25 #include "libavutil/common.h"
26 #include "libavutil/mem.h"
28 #include "timefilter.h"
31 // Delay Locked Loop data. These variables refer to mathematical
32 // concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf
34 double feedback2_factor;
35 double feedback3_factor;
40 /* 1 - exp(-x) using a 3-order power series */
41 static double qexpneg(double x)
43 return 1 - 1 / (1 + x * (1 + x / 2 * (1 + x / 3)));
46 TimeFilter *ff_timefilter_new(double time_base,
50 TimeFilter *self = av_mallocz(sizeof(TimeFilter));
51 double o = 2 * M_PI * bandwidth * period * time_base;
56 self->clock_period = time_base;
57 self->feedback2_factor = qexpneg(M_SQRT2 * o);
58 self->feedback3_factor = qexpneg(o * o) / period;
62 void ff_timefilter_destroy(TimeFilter *self)
67 void ff_timefilter_reset(TimeFilter *self)
72 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
75 if (self->count == 1) {
76 self->cycle_time = system_time;
79 self->cycle_time += self->clock_period * period;
80 loop_error = system_time - self->cycle_time;
82 self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
83 self->clock_period += self->feedback3_factor * loop_error;
85 return self->cycle_time;
88 double ff_timefilter_eval(TimeFilter *self, double delta)
90 return self->cycle_time + self->clock_period * delta;