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