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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 FFmpeg. | |
9 | * | |
10 | * FFmpeg 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 | * FFmpeg 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 FFmpeg; 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 | /* 1 - exp(-x) using a 3-order power series */ | |
41 | static double qexpneg(double x) | |
42 | { | |
43 | return 1 - 1 / (1 + x * (1 + x / 2 * (1 + x / 3))); | |
44 | } | |
45 | ||
46 | TimeFilter *ff_timefilter_new(double time_base, | |
47 | double period, | |
48 | double bandwidth) | |
49 | { | |
50 | TimeFilter *self = av_mallocz(sizeof(TimeFilter)); | |
51 | double o = 2 * M_PI * bandwidth * period * time_base; | |
52 | ||
53 | if (!self) | |
54 | return NULL; | |
55 | ||
56 | self->clock_period = time_base; | |
57 | self->feedback2_factor = qexpneg(M_SQRT2 * o); | |
58 | self->feedback3_factor = qexpneg(o * o) / period; | |
59 | return self; | |
60 | } | |
61 | ||
62 | void ff_timefilter_destroy(TimeFilter *self) | |
63 | { | |
64 | av_freep(&self); | |
65 | } | |
66 | ||
67 | void ff_timefilter_reset(TimeFilter *self) | |
68 | { | |
69 | self->count = 0; | |
70 | } | |
71 | ||
72 | double ff_timefilter_update(TimeFilter *self, double system_time, double period) | |
73 | { | |
74 | self->count++; | |
75 | if (self->count == 1) { | |
76 | self->cycle_time = system_time; | |
77 | } else { | |
78 | double loop_error; | |
79 | self->cycle_time += self->clock_period * period; | |
80 | loop_error = system_time - self->cycle_time; | |
81 | ||
82 | self->cycle_time += FFMAX(self->feedback2_factor, 1.0 / self->count) * loop_error; | |
83 | self->clock_period += self->feedback3_factor * loop_error; | |
84 | } | |
85 | return self->cycle_time; | |
86 | } | |
87 | ||
88 | double ff_timefilter_eval(TimeFilter *self, double delta) | |
89 | { | |
90 | return self->cycle_time + self->clock_period * delta; | |
91 | } | |
92 | ||
93 | #ifdef TEST | |
94 | #include "libavutil/lfg.h" | |
95 | #define LFG_MAX ((1LL << 32) - 1) | |
96 | ||
97 | int main(void) | |
98 | { | |
99 | AVLFG prng; | |
100 | double n0, n1; | |
101 | #define SAMPLES 1000 | |
102 | double ideal[SAMPLES]; | |
103 | double samples[SAMPLES]; | |
104 | double samplet[SAMPLES]; | |
105 | for (n0 = 0; n0 < 40; n0 = 2 * n0 + 1) { | |
106 | for (n1 = 0; n1 < 10; n1 = 2 * n1 + 1) { | |
107 | double best_error = 1000000000; | |
108 | double bestpar0 = n0 ? 1 : 100000; | |
109 | double bestpar1 = 1; | |
110 | int better, i; | |
111 | ||
112 | av_lfg_init(&prng, 123); | |
113 | for (i = 0; i < SAMPLES; i++) { | |
114 | samplet[i] = 10 + i + (av_lfg_get(&prng) < LFG_MAX/2 ? 0 : 0.999); | |
115 | ideal[i] = samplet[i] + n1 * i / (1000); | |
116 | samples[i] = ideal[i] + n0 * (av_lfg_get(&prng) - LFG_MAX / 2) / (LFG_MAX * 10LL); | |
117 | if(i && samples[i]<samples[i-1]) | |
118 | samples[i]=samples[i-1]+0.001; | |
119 | } | |
120 | ||
121 | do { | |
122 | double par0, par1; | |
123 | better = 0; | |
124 | for (par0 = bestpar0 * 0.8; par0 <= bestpar0 * 1.21; par0 += bestpar0 * 0.05) { | |
125 | for (par1 = bestpar1 * 0.8; par1 <= bestpar1 * 1.21; par1 += bestpar1 * 0.05) { | |
126 | double error = 0; | |
127 | TimeFilter *tf = ff_timefilter_new(1, par0, par1); | |
128 | if (!tf) { | |
129 | printf("Could not allocate memory for timefilter.\n"); | |
130 | exit(1); | |
131 | } | |
132 | for (i = 0; i < SAMPLES; i++) { | |
133 | double filtered; | |
134 | filtered = ff_timefilter_update(tf, samples[i], i ? (samplet[i] - samplet[i-1]) : 1); | |
135 | if(filtered < 0 || filtered > 1000000000) | |
136 | printf("filter is unstable\n"); | |
137 | error += (filtered - ideal[i]) * (filtered - ideal[i]); | |
138 | } | |
139 | ff_timefilter_destroy(tf); | |
140 | if (error < best_error) { | |
141 | best_error = error; | |
142 | bestpar0 = par0; | |
143 | bestpar1 = par1; | |
144 | better = 1; | |
145 | } | |
146 | } | |
147 | } | |
148 | } while (better); | |
149 | #if 0 | |
150 | double lastfil = 9; | |
151 | TimeFilter *tf = ff_timefilter_new(1, bestpar0, bestpar1); | |
152 | for (i = 0; i < SAMPLES; i++) { | |
153 | double filtered; | |
154 | filtered = ff_timefilter_update(tf, samples[i], 1); | |
155 | printf("%f %f %f %f\n", i - samples[i] + 10, filtered - samples[i], | |
156 | samples[FFMAX(i, 1)] - samples[FFMAX(i - 1, 0)], filtered - lastfil); | |
157 | lastfil = filtered; | |
158 | } | |
159 | ff_timefilter_destroy(tf); | |
160 | #else | |
161 | printf(" [%12f %11f %9f]", bestpar0, bestpar1, best_error); | |
162 | #endif | |
163 | } | |
164 | printf("\n"); | |
165 | } | |
166 | return 0; | |
167 | } | |
168 | #endif |