/* * Delay Locked Loop based time filter * Copyright (c) 2009 Samalyse * Copyright (c) 2009 Michael Niedermayer * Author: Olivier Guilyardi <olivier samalyse com> * Michael Niedermayer <michaelni gmx at> * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include "libavutil/common.h" #include "libavutil/mem.h" #include "timefilter.h" struct TimeFilter { // Delay Locked Loop data. These variables refer to mathematical // concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf double cycle_time; double feedback2_factor; double feedback3_factor; double clock_period; int count; }; /* 1 - exp(-x) using a 3-order power series */ static double qexpneg(double x) { return 1 - 1 / (1 + x * (1 + x / 2 * (1 + x / 3))); } TimeFilter *ff_timefilter_new(double time_base, double period, double bandwidth) { TimeFilter *self = av_mallocz(sizeof(TimeFilter)); double o = 2 * M_PI * bandwidth * period * time_base; if (!self) return NULL; self->clock_period = time_base; self->feedback2_factor = qexpneg(M_SQRT2 * o); self->feedback3_factor = qexpneg(o * o) / period; return self; } void ff_timefilter_destroy(TimeFilter *self) { av_freep(&self); } void ff_timefilter_reset(TimeFilter *self) { self->count = 0; } double ff_timefilter_update(TimeFilter *self, double system_time, double period) { self->count++; if (self->count == 1) { self->cycle_time = system_time; } else { double loop_error; self->cycle_time += self->clock_period * period; loop_error = system_time - self->cycle_time; self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error; self->clock_period += self->feedback3_factor * loop_error; } return self->cycle_time; } double ff_timefilter_eval(TimeFilter *self, double delta) { return self->cycle_time + self->clock_period * delta; }