libavdevice/timefilter.c

   1 /*
   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>
   7  *
   8  * This file is part of Libav.
   9  *
  10  * Libav 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  * Libav 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 Libav; if not, write to the Free Software
  22  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  23  */
  24
  25 #include "libavutil/common.h"
  26 #include "libavutil/mem.h"
  27 #include "config.h"
  28 #include "timefilter.h"
  29
  30 struct TimeFilter {
  31     // Delay Locked Loop data. These variables refer to mathematical
  32     // concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf
  33     double cycle_time;
  34     double feedback2_factor;
  35     double feedback3_factor;
  36     double clock_period;
  37     int count;
  38 };
  39
  40 TimeFilter *ff_timefilter_new(double clock_period,
  41                               double feedback2_factor,
  42                               double feedback3_factor)
  43 {
  44     TimeFilter *self       = av_mallocz(sizeof(TimeFilter));
  45     self->clock_period     = clock_period;
  46     self->feedback2_factor = feedback2_factor;
  47     self->feedback3_factor = feedback3_factor;
  48     return self;
  49 }
  50
  51 void ff_timefilter_destroy(TimeFilter *self)
  52 {
  53     av_freep(&self);
  54 }
  55
  56 void ff_timefilter_reset(TimeFilter *self)
  57 {
  58     self->count = 0;
  59 }
  60
  61 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
  62 {
  63     self->count++;
  64     if (self->count == 1) {
  65         self->cycle_time = system_time;
  66     } else {
  67         double loop_error;
  68         self->cycle_time += self->clock_period * period;
  69         loop_error = system_time - self->cycle_time;
  70
  71         self->cycle_time   += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
  72         self->clock_period += self->feedback3_factor * loop_error / period;
  73     }
  74     return self->cycle_time;
  75 }
  76
  77 #ifdef TEST
  78 #include "libavutil/lfg.h"
  79 #define LFG_MAX ((1LL << 32) - 1)
  80
  81 int main(void)
  82 {
  83     AVLFG prng;
  84     double n0, n1;
  85 #define SAMPLES 1000
  86     double ideal[SAMPLES];
  87     double samples[SAMPLES];
  88     for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) {
  89         for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) {
  90             double best_error = 1000000000;
  91             double bestpar0   = 1;
  92             double bestpar1   = 0.001;
  93             int better, i;
  94
  95             av_lfg_init(&prng, 123);
  96             for (i = 0; i < SAMPLES; i++) {
  97                 ideal[i]   = 10 + i + n1 * i / (1000);
  98                 samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2) / (LFG_MAX * 10LL);
  99             }
 100
 101             do {
 102                 double par0, par1;
 103                 better = 0;
 104                 for (par0 = bestpar0 * 0.8; par0 <= bestpar0 * 1.21; par0 += bestpar0 * 0.05) {
 105                     for (par1 = bestpar1 * 0.8; par1 <= bestpar1 * 1.21; par1 += bestpar1 * 0.05) {
 106                         double error   = 0;
 107                         TimeFilter *tf = ff_timefilter_new(1, par0, par1);
 108                         for (i = 0; i < SAMPLES; i++) {
 109                             double filtered;
 110                             filtered = ff_timefilter_update(tf, samples[i], 1);
 111                             error   += (filtered - ideal[i]) * (filtered - ideal[i]);
 112                         }
 113                         ff_timefilter_destroy(tf);
 114                         if (error < best_error) {
 115                             best_error = error;
 116                             bestpar0   = par0;
 117                             bestpar1   = par1;
 118                             better     = 1;
 119                         }
 120                     }
 121                 }
 122             } while (better);
 123 #if 0
 124             double lastfil = 9;
 125             TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1);
 126             for (i = 0; i < SAMPLES; i++) {
 127                 double filtered;
 128                 filtered = ff_timefilter_update(tf, samples[i], 1);
 129                 printf("%f %f %f %f\n", i - samples[i] + 10, filtered - samples[i],
 130                        samples[FFMAX(i, 1)] - samples[FFMAX(i - 1, 0)], filtered - lastfil);
 131                 lastfil = filtered;
 132             }
 133             ff_timefilter_destroy(tf);
 134 #else
 135             printf(" [%f %f %9f]", bestpar0, bestpar1, best_error);
 136 #endif
 137         }
 138         printf("\n");
 139     }
 140     return 0;
 141 }
 142 #endif