1 /*
2 * Copyright (c) 2011 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 #include "webrtc/system_wrappers/interface/timestamp_extrapolator.h"
12
13 #include <algorithm>
14
15 namespace webrtc {
16
TimestampExtrapolator(int64_t start_ms)17 TimestampExtrapolator::TimestampExtrapolator(int64_t start_ms)
18 : _rwLock(RWLockWrapper::CreateRWLock()),
19 _startMs(0),
20 _firstTimestamp(0),
21 _wrapArounds(0),
22 _prevUnwrappedTimestamp(-1),
23 _prevWrapTimestamp(-1),
24 _lambda(1),
25 _firstAfterReset(true),
26 _packetCount(0),
27 _startUpFilterDelayInPackets(2),
28 _detectorAccumulatorPos(0),
29 _detectorAccumulatorNeg(0),
30 _alarmThreshold(60e3),
31 _accDrift(6600), // in timestamp ticks, i.e. 15 ms
32 _accMaxError(7000),
33 _P11(1e10) {
34 Reset(start_ms);
35 }
36
~TimestampExtrapolator()37 TimestampExtrapolator::~TimestampExtrapolator()
38 {
39 delete _rwLock;
40 }
41
Reset(int64_t start_ms)42 void TimestampExtrapolator::Reset(int64_t start_ms)
43 {
44 WriteLockScoped wl(*_rwLock);
45 _startMs = start_ms;
46 _prevMs = _startMs;
47 _firstTimestamp = 0;
48 _w[0] = 90.0;
49 _w[1] = 0;
50 _P[0][0] = 1;
51 _P[1][1] = _P11;
52 _P[0][1] = _P[1][0] = 0;
53 _firstAfterReset = true;
54 _prevUnwrappedTimestamp = -1;
55 _prevWrapTimestamp = -1;
56 _wrapArounds = 0;
57 _packetCount = 0;
58 _detectorAccumulatorPos = 0;
59 _detectorAccumulatorNeg = 0;
60 }
61
62 void
Update(int64_t tMs,uint32_t ts90khz)63 TimestampExtrapolator::Update(int64_t tMs, uint32_t ts90khz)
64 {
65
66 _rwLock->AcquireLockExclusive();
67 if (tMs - _prevMs > 10e3)
68 {
69 // Ten seconds without a complete frame.
70 // Reset the extrapolator
71 _rwLock->ReleaseLockExclusive();
72 Reset(tMs);
73 _rwLock->AcquireLockExclusive();
74 }
75 else
76 {
77 _prevMs = tMs;
78 }
79
80 // Remove offset to prevent badly scaled matrices
81 tMs -= _startMs;
82
83 CheckForWrapArounds(ts90khz);
84
85 int64_t unwrapped_ts90khz = static_cast<int64_t>(ts90khz) +
86 _wrapArounds * ((static_cast<int64_t>(1) << 32) - 1);
87
88 if (_prevUnwrappedTimestamp >= 0 &&
89 unwrapped_ts90khz < _prevUnwrappedTimestamp)
90 {
91 // Drop reordered frames.
92 _rwLock->ReleaseLockExclusive();
93 return;
94 }
95
96 if (_firstAfterReset)
97 {
98 // Make an initial guess of the offset,
99 // should be almost correct since tMs - _startMs
100 // should about zero at this time.
101 _w[1] = -_w[0] * tMs;
102 _firstTimestamp = unwrapped_ts90khz;
103 _firstAfterReset = false;
104 }
105
106 double residual =
107 (static_cast<double>(unwrapped_ts90khz) - _firstTimestamp) -
108 static_cast<double>(tMs) * _w[0] - _w[1];
109 if (DelayChangeDetection(residual) &&
110 _packetCount >= _startUpFilterDelayInPackets)
111 {
112 // A sudden change of average network delay has been detected.
113 // Force the filter to adjust its offset parameter by changing
114 // the offset uncertainty. Don't do this during startup.
115 _P[1][1] = _P11;
116 }
117 //T = [t(k) 1]';
118 //that = T'*w;
119 //K = P*T/(lambda + T'*P*T);
120 double K[2];
121 K[0] = _P[0][0] * tMs + _P[0][1];
122 K[1] = _P[1][0] * tMs + _P[1][1];
123 double TPT = _lambda + tMs * K[0] + K[1];
124 K[0] /= TPT;
125 K[1] /= TPT;
126 //w = w + K*(ts(k) - that);
127 _w[0] = _w[0] + K[0] * residual;
128 _w[1] = _w[1] + K[1] * residual;
129 //P = 1/lambda*(P - K*T'*P);
130 double p00 = 1 / _lambda * (_P[0][0] - (K[0] * tMs * _P[0][0] + K[0] * _P[1][0]));
131 double p01 = 1 / _lambda * (_P[0][1] - (K[0] * tMs * _P[0][1] + K[0] * _P[1][1]));
132 _P[1][0] = 1 / _lambda * (_P[1][0] - (K[1] * tMs * _P[0][0] + K[1] * _P[1][0]));
133 _P[1][1] = 1 / _lambda * (_P[1][1] - (K[1] * tMs * _P[0][1] + K[1] * _P[1][1]));
134 _P[0][0] = p00;
135 _P[0][1] = p01;
136 _prevUnwrappedTimestamp = unwrapped_ts90khz;
137 if (_packetCount < _startUpFilterDelayInPackets)
138 {
139 _packetCount++;
140 }
141 _rwLock->ReleaseLockExclusive();
142 }
143
144 int64_t
ExtrapolateLocalTime(uint32_t timestamp90khz)145 TimestampExtrapolator::ExtrapolateLocalTime(uint32_t timestamp90khz)
146 {
147 ReadLockScoped rl(*_rwLock);
148 int64_t localTimeMs = 0;
149 CheckForWrapArounds(timestamp90khz);
150 double unwrapped_ts90khz = static_cast<double>(timestamp90khz) +
151 _wrapArounds * ((static_cast<int64_t>(1) << 32) - 1);
152 if (_packetCount == 0)
153 {
154 localTimeMs = -1;
155 }
156 else if (_packetCount < _startUpFilterDelayInPackets)
157 {
158 localTimeMs = _prevMs + static_cast<int64_t>(
159 static_cast<double>(unwrapped_ts90khz - _prevUnwrappedTimestamp) /
160 90.0 + 0.5);
161 }
162 else
163 {
164 if (_w[0] < 1e-3)
165 {
166 localTimeMs = _startMs;
167 }
168 else
169 {
170 double timestampDiff = unwrapped_ts90khz -
171 static_cast<double>(_firstTimestamp);
172 localTimeMs = static_cast<int64_t>(
173 static_cast<double>(_startMs) + (timestampDiff - _w[1]) /
174 _w[0] + 0.5);
175 }
176 }
177 return localTimeMs;
178 }
179
180 // Investigates if the timestamp clock has overflowed since the last timestamp and
181 // keeps track of the number of wrap arounds since reset.
182 void
CheckForWrapArounds(uint32_t ts90khz)183 TimestampExtrapolator::CheckForWrapArounds(uint32_t ts90khz)
184 {
185 if (_prevWrapTimestamp == -1)
186 {
187 _prevWrapTimestamp = ts90khz;
188 return;
189 }
190 if (ts90khz < _prevWrapTimestamp)
191 {
192 // This difference will probably be less than -2^31 if we have had a wrap around
193 // (e.g. timestamp = 1, _previousTimestamp = 2^32 - 1). Since it is casted to a Word32,
194 // it should be positive.
195 if (static_cast<int32_t>(ts90khz - _prevWrapTimestamp) > 0)
196 {
197 // Forward wrap around
198 _wrapArounds++;
199 }
200 }
201 // This difference will probably be less than -2^31 if we have had a backward wrap around.
202 // Since it is casted to a Word32, it should be positive.
203 else if (static_cast<int32_t>(_prevWrapTimestamp - ts90khz) > 0)
204 {
205 // Backward wrap around
206 _wrapArounds--;
207 }
208 _prevWrapTimestamp = ts90khz;
209 }
210
211 bool
DelayChangeDetection(double error)212 TimestampExtrapolator::DelayChangeDetection(double error)
213 {
214 // CUSUM detection of sudden delay changes
215 error = (error > 0) ? std::min(error, _accMaxError) :
216 std::max(error, -_accMaxError);
217 _detectorAccumulatorPos =
218 std::max(_detectorAccumulatorPos + error - _accDrift, (double)0);
219 _detectorAccumulatorNeg =
220 std::min(_detectorAccumulatorNeg + error + _accDrift, (double)0);
221 if (_detectorAccumulatorPos > _alarmThreshold || _detectorAccumulatorNeg < -_alarmThreshold)
222 {
223 // Alarm
224 _detectorAccumulatorPos = _detectorAccumulatorNeg = 0;
225 return true;
226 }
227 return false;
228 }
229
230 }
231