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 integrator2_state;
  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->integrator2_state = 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->integrator2_state * 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->integrator2_state += self->feedback3_factor * loop_error / period;
  72     }
  73     return self->cycle_time;
  74 }
  75
  76 #ifdef TEST
  77 main(){
  78     double n0,n1;
  79 #define SAMPLES 1000
  80     double ideal[SAMPLES];
  81     double samples[SAMPLES];
  82     for(n0= 0; n0<40; n0=2*n0+1){
  83         for(n1= 0; n1<10; n1=2*n1+1){
  84             double best_error= 1000000000;
  85             double bestpar0=1;
  86             double bestpar1=0.001;
  87             int better, i;
  88
  89             srandom(123);
  90             for(i=0; i<SAMPLES; i++){
  91                 ideal[i]  = 10 + i + n1*i/(1000);
  92                 samples[i]= ideal[i] + n0*(rand()-RAND_MAX/2)/(RAND_MAX*10LL);
  93             }
  94
  95             do{
  96                 double par0, par1;
  97                 better=0;
  98                 for(par0= bestpar0*0.8; par0<=bestpar0*1.21; par0+=bestpar0*0.05){
  99                     for(par1= bestpar1*0.8; par1<=bestpar1*1.21; par1+=bestpar1*0.05){
 100                         double error=0;
 101                         TimeFilter *tf= ff_timefilter_new(1, par0, par1);
 102                         for(i=0; i<SAMPLES; i++){
 103                             double filtered;
 104                             filtered=  ff_timefilter_update(tf, samples[i], 1);
 105                             error += (filtered - ideal[i]) * (filtered - ideal[i]);
 106                         }
 107                         ff_timefilter_destroy(tf);
 108                         if(error < best_error){
 109                             best_error= error;
 110                             bestpar0= par0;
 111                             bestpar1= par1;
 112                             better=1;
 113                         }
 114                     }
 115                 }
 116             }while(better);
 117             printf(" [%f %f %f]", bestpar0, bestpar1, best_error);
 118         }
 119         printf("\n");
 120     }
 121 }
 122 #endif