timefilter.c
Go to the documentation of this file.
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 
26 #include "config.h"
27 #include "timefilter.h"
28 #include "libavutil/mem.h"
29 
30 struct TimeFilter {
33  double cycle_time;
36  double clock_period;
37  int count;
38 };
39 
40 TimeFilter * ff_timefilter_new(double clock_period, double feedback2_factor, double feedback3_factor)
41 {
42  TimeFilter *self = av_mallocz(sizeof(TimeFilter));
43  self->clock_period = clock_period;
44  self->feedback2_factor = feedback2_factor;
45  self->feedback3_factor = feedback3_factor;
46  return self;
47 }
48 
50 {
51  av_freep(&self);
52 }
53 
55 {
56  self->count = 0;
57 }
58 
59 double ff_timefilter_update(TimeFilter *self, double system_time, double period)
60 {
61  self->count++;
62  if (self->count==1) {
64  self->cycle_time = system_time;
65  } else {
66  double loop_error;
67  self->cycle_time += self->clock_period * period;
69  loop_error = system_time - self->cycle_time;
70 
72  self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error;
73  self->clock_period += self->feedback3_factor * loop_error / period;
74  }
75  return self->cycle_time;
76 }
77 
78 #ifdef TEST
79 #include "libavutil/lfg.h"
80 #define LFG_MAX ((1LL << 32) - 1)
81 
82 #undef printf
83 
84 int main(void)
85 {
86  AVLFG prng;
87  double n0,n1;
88 #define SAMPLES 1000
89  double ideal[SAMPLES];
90  double samples[SAMPLES];
91 #if 1
92  for(n0= 0; n0<40; n0=2*n0+1){
93  for(n1= 0; n1<10; n1=2*n1+1){
94 #else
95  {{
96  n0=7;
97  n1=1;
98 #endif
99  double best_error= 1000000000;
100  double bestpar0=1;
101  double bestpar1=0.001;
102  int better, i;
103 
104  av_lfg_init(&prng, 123);
105  for(i=0; i<SAMPLES; i++){
106  ideal[i] = 10 + i + n1*i/(1000);
107  samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2)
108  / (LFG_MAX * 10LL);
109  }
110 
111  do{
112  double par0, par1;
113  better=0;
114  for(par0= bestpar0*0.8; par0<=bestpar0*1.21; par0+=bestpar0*0.05){
115  for(par1= bestpar1*0.8; par1<=bestpar1*1.21; par1+=bestpar1*0.05){
116  double error=0;
117  TimeFilter *tf= ff_timefilter_new(1, par0, par1);
118  for(i=0; i<SAMPLES; i++){
119  double filtered;
120  filtered= ff_timefilter_update(tf, samples[i], 1);
121  error += (filtered - ideal[i]) * (filtered - ideal[i]);
122  }
124  if(error < best_error){
125  best_error= error;
126  bestpar0= par0;
127  bestpar1= par1;
128  better=1;
129  }
130  }
131  }
132  }while(better);
133 #if 0
134  double lastfil=9;
135  TimeFilter *tf= ff_timefilter_new(1, bestpar0, bestpar1);
136  for(i=0; i<SAMPLES; i++){
137  double filtered;
138  filtered= ff_timefilter_update(tf, samples[i], 1);
139  printf("%f %f %f %f\n", i - samples[i] + 10, filtered - samples[i], samples[FFMAX(i, 1)] - samples[FFMAX(i-1, 0)], filtered - lastfil);
140  lastfil= filtered;
141  }
143 #else
144  printf(" [%f %f %9f]", bestpar0, bestpar1, best_error);
145 #endif
146  }
147  printf("\n");
148  }
149  return 0;
150 }
151 #endif