git.sesse.net Git - ffmpeg/blob - libavformat/timefilter.c

   1 /*
   2  * Delay Locked Loop based time filter
   3  * Copyright (c) 2009 Samalyse
   4  * Author: Olivier Guilyardi <olivier samalyse com>
   5  *
   6  * This file is part of FFmpeg.
   7  *
   8  * FFmpeg is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * FFmpeg is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with FFmpeg; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23
  24 #include "config.h"
  25 #include "avformat.h"
  26 #include "timefilter.h"
  27
  28 struct TimeFilter {
  29     /// Delay Locked Loop data. These variables refer to mathematical
  30     /// concepts described in: http://www.kokkinizita.net/papers/usingdll.pdf
  31     double cycle_time;
  32     double feedback2_factor;
  33     double feedback3_factor;
  34     double clock_period;
  35     int count;
  36 };
  37
  38 TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor)
  39 {
  40     TimeFilter *self        = av_mallocz(sizeof(TimeFilter));
  41     self->clock_period      = clock_period;
  42     self->feedback2_factor  = feedback2_factor;
  43     self->feedback3_factor  = feedback3_factor;
  44     return self;
  45 }
  46
  47 void ff_timefilter_destroy(TimeFilter *self)
  48 {
  49     av_freep(&self);
  50 }
  51
  52 void ff_timefilter_reset(TimeFilter *self)
  53 {
  54     self->count      = 0;
  55 }
  56
  57 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
  58 {
  59     self->count++;
  60     if (self->count==1) {
  61         /// init loop
  62         self->cycle_time    = system_time;
  63     } else {
  64         double loop_error;
  65         self->cycle_time   += self->clock_period * period;
  66         /// calculate loop error
  67         loop_error          = system_time - self->cycle_time;
  68
  69         /// update loop
  70         self->cycle_time   += FFMAX(self->feedback2_factor, 1.0/(self->count)) * loop_error;
  71         self->clock_period += self->feedback3_factor * loop_error / period;
  72     }
  73     return self->cycle_time;
  74 }
  75
  76 #ifdef TEST
  77 #undef rand
  78 int main(void)
  79 {
  80     double n0,n1;
  81 #define SAMPLES 1000
  82     double ideal[SAMPLES];
  83     double samples[SAMPLES];
  84     for(n0= 0; n0<40; n0=2*n0+1){
  85         for(n1= 0; n1<10; n1=2*n1+1){
  86             double best_error= 1000000000;
  87             double bestpar0=1;
  88             double bestpar1=0.001;
  89             int better, i;
  90
  91             srandom(123);
  92             for(i=0; i<SAMPLES; i++){
  93                 ideal[i]  = 10 + i + n1*i/(1000);
  94                 samples[i]= ideal[i] + n0*(rand()-RAND_MAX/2)/(RAND_MAX*10LL);
  95             }
  96
  97             do{
  98                 double par0, par1;
  99                 better=0;
 100                 for(par0= bestpar0*0.8; par0<=bestpar0*1.21; par0+=bestpar0*0.05){
 101                     for(par1= bestpar1*0.8; par1<=bestpar1*1.21; par1+=bestpar1*0.05){
 102                         double error=0;
 103                         TimeFilter *tf= ff_timefilter_new(1, par0, par1);
 104                         for(i=0; i<SAMPLES; i++){
 105                             double filtered;
 106                             filtered=  ff_timefilter_update(tf, samples[i], 1);
 107                             error += (filtered - ideal[i]) * (filtered - ideal[i]);
 108                         }
 109                         ff_timefilter_destroy(tf);
 110                         if(error < best_error){
 111                             best_error= error;
 112                             bestpar0= par0;
 113                             bestpar1= par1;
 114                             better=1;
 115                         }
 116                     }
 117                 }
 118             }while(better);
 119             printf(" [%f %f %f]", bestpar0, bestpar1, best_error);
 120         }
 121         printf("\n");
 122     }
 123     return 0;
 124 }
 125 #endif