| OLD | NEW |
|---|
| (Empty) |
| 1 /* | |
| 2 * Copyright 2016 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 <math.h> | |
| 12 | |
| 13 #include <algorithm> | |
| 14 #include <limits> | |
| 15 | |
| 16 #include "webrtc/base/gunit.h" | |
| 17 #include "webrtc/base/random.h" | |
| 18 #include "webrtc/base/timestampaligner.h" | |
| 19 | |
| 20 namespace rtc { | |
| 21 | |
| 22 namespace { | |
| 23 // Computes the difference x_k - mean(x), when x_k is the linear sequence x_k = | |
| 24 // k, and the "mean" is plain mean for the first |window_size| samples, followed | |
| 25 // by exponential averaging with weight 1 / |window_size| for each new sample. | |
| 26 // This is needed to predict the effect of camera clock drift on the timestamp | |
| 27 // translation. See the comment on TimestampAligner::UpdateOffset for more | |
| 28 // context. | |
| 29 double MeanTimeDifference(int nsamples, int window_size) { | |
| 30 if (nsamples <= window_size) { | |
| 31 // Plain averaging. | |
| 32 return nsamples / 2.0; | |
| 33 } else { | |
| 34 // Exponential convergence towards | |
| 35 // interval_error * (window_size - 1) | |
| 36 double alpha = 1.0 - 1.0 / window_size; | |
| 37 | |
| 38 return ((window_size - 1) - | |
| 39 (window_size / 2.0 - 1) * pow(alpha, nsamples - window_size)); | |
| 40 } | |
| 41 } | |
| 42 | |
| 43 class TimestampAlignerForTest : public TimestampAligner { | |
| 44 // Make internal methods accessible to testing. | |
| 45 public: | |
| 46 using TimestampAligner::UpdateOffset; | |
| 47 using TimestampAligner::ClipTimestamp; | |
| 48 }; | |
| 49 | |
| 50 void TestTimestampFilter(double rel_freq_error) { | |
| 51 TimestampAlignerForTest timestamp_aligner_for_test; | |
| 52 TimestampAligner timestamp_aligner; | |
| 53 const int64_t kEpoch = 10000; | |
| 54 const int64_t kJitterUs = 5000; | |
| 55 const int64_t kIntervalUs = 33333; // 30 FPS | |
| 56 const int kWindowSize = 100; | |
| 57 const int kNumFrames = 3 * kWindowSize; | |
| 58 | |
| 59 int64_t interval_error_us = kIntervalUs * rel_freq_error; | |
| 60 int64_t system_start_us = rtc::TimeMicros(); | |
| 61 webrtc::Random random(17); | |
| 62 | |
| 63 int64_t prev_translated_time_us = system_start_us; | |
| 64 | |
| 65 for (int i = 0; i < kNumFrames; i++) { | |
| 66 // Camera time subject to drift. | |
| 67 int64_t camera_time_us = kEpoch + i * (kIntervalUs + interval_error_us); | |
| 68 int64_t system_time_us = system_start_us + i * kIntervalUs; | |
| 69 // And system time readings are subject to jitter. | |
| 70 int64_t system_measured_us = system_time_us + random.Rand(kJitterUs); | |
| 71 | |
| 72 int64_t offset_us = timestamp_aligner_for_test.UpdateOffset( | |
| 73 camera_time_us, system_measured_us); | |
| 74 | |
| 75 int64_t filtered_time_us = camera_time_us + offset_us; | |
| 76 int64_t translated_time_us = timestamp_aligner_for_test.ClipTimestamp( | |
| 77 filtered_time_us, system_measured_us); | |
| 78 | |
| 79 // Check that we get identical result from the all-in-one helper method. | |
| 80 ASSERT_EQ(translated_time_us, timestamp_aligner.TranslateTimestamp( | |
| 81 camera_time_us, system_measured_us)); | |
| 82 | |
| 83 EXPECT_LE(translated_time_us, system_measured_us); | |
| 84 EXPECT_GE(translated_time_us, | |
| 85 prev_translated_time_us + rtc::kNumMicrosecsPerMillisec); | |
| 86 | |
| 87 // The relative frequency error contributes to the expected error | |
| 88 // by a factor which is the difference between the current time | |
| 89 // and the average of earlier sample times. | |
| 90 int64_t expected_error_us = | |
| 91 kJitterUs / 2 + | |
| 92 rel_freq_error * kIntervalUs * MeanTimeDifference(i, kWindowSize); | |
| 93 | |
| 94 int64_t bias_us = filtered_time_us - translated_time_us; | |
| 95 EXPECT_GE(bias_us, 0); | |
| 96 | |
| 97 if (i == 0) { | |
| 98 EXPECT_EQ(translated_time_us, system_measured_us); | |
| 99 } else { | |
| 100 EXPECT_NEAR(filtered_time_us, system_time_us + expected_error_us, | |
| 101 2.0 * kJitterUs / sqrt(std::max(i, kWindowSize))); | |
| 102 } | |
| 103 // If the camera clock runs too fast (rel_freq_error > 0.0), The | |
| 104 // bias is expected to roughly cancel the expected error from the | |
| 105 // clock drift, as this grows. Otherwise, it reflects the | |
| 106 // measurement noise. The tolerances here were selected after some | |
| 107 // trial and error. | |
| 108 if (i < 10 || rel_freq_error <= 0.0) { | |
| 109 EXPECT_LE(bias_us, 3000); | |
| 110 } else { | |
| 111 EXPECT_NEAR(bias_us, expected_error_us, 1500); | |
| 112 } | |
| 113 prev_translated_time_us = translated_time_us; | |
| 114 } | |
| 115 } | |
| 116 | |
| 117 } // Anonymous namespace | |
| 118 | |
| 119 TEST(TimestampAlignerTest, AttenuateTimestampJitterNoDrift) { | |
| 120 TestTimestampFilter(0.0); | |
| 121 } | |
| 122 | |
| 123 // 100 ppm is a worst case for a reasonable crystal. | |
| 124 TEST(TimestampAlignerTest, AttenuateTimestampJitterSmallPosDrift) { | |
| 125 TestTimestampFilter(0.0001); | |
| 126 } | |
| 127 | |
| 128 TEST(TimestampAlignerTest, AttenuateTimestampJitterSmallNegDrift) { | |
| 129 TestTimestampFilter(-0.0001); | |
| 130 } | |
| 131 | |
| 132 // 3000 ppm, 3 ms / s, is the worst observed drift, see | |
| 133 // https://bugs.chromium.org/p/webrtc/issues/detail?id=5456 | |
| 134 TEST(TimestampAlignerTest, AttenuateTimestampJitterLargePosDrift) { | |
| 135 TestTimestampFilter(0.003); | |
| 136 } | |
| 137 | |
| 138 TEST(TimestampAlignerTest, AttenuateTimestampJitterLargeNegDrift) { | |
| 139 TestTimestampFilter(-0.003); | |
| 140 } | |
| 141 | |
| 142 // Exhibits a mostly hypothetical problem, where certain inputs to the | |
| 143 // TimestampAligner.UpdateOffset filter result in non-monotonous | |
| 144 // translated timestamps. This test verifies that the ClipTimestamp | |
| 145 // logic handles this case correctly. | |
| 146 TEST(TimestampAlignerTest, ClipToMonotonous) { | |
| 147 TimestampAlignerForTest timestamp_aligner; | |
| 148 | |
| 149 // For system time stamps { 0, s1, s1 + s2 }, and camera timestamps | |
| 150 // {0, c1, c1 + c2}, we exhibit non-monotonous behaviour if and only | |
| 151 // if c1 > s1 + 2 s2 + 4 c2. | |
| 152 const int kNumSamples = 3; | |
| 153 const int64_t camera_time_us[kNumSamples] = {0, 80000, 90001}; | |
| 154 const int64_t system_time_us[kNumSamples] = {0, 10000, 20000}; | |
| 155 const int64_t expected_offset_us[kNumSamples] = {0, -35000, -46667}; | |
| 156 | |
| 157 // Non-monotonic translated timestamps can happen when only for | |
| 158 // translated timestamps in the future. Which is tolerated if | |
| 159 // |timestamp_aligner.clip_bias_us| is large enough. Instead of | |
| 160 // changing that private member for this test, just add the bias to | |
| 161 // |system_time_us| when calling ClipTimestamp. | |
| 162 const int64_t kClipBiasUs = 100000; | |
| 163 | |
| 164 bool did_clip = false; | |
| 165 int64_t prev_timestamp_us = std::numeric_limits<int64_t>::min(); | |
| 166 for (int i = 0; i < kNumSamples; i++) { | |
| 167 int64_t offset_us = | |
| 168 timestamp_aligner.UpdateOffset(camera_time_us[i], system_time_us[i]); | |
| 169 EXPECT_EQ(offset_us, expected_offset_us[i]); | |
| 170 | |
| 171 int64_t translated_timestamp_us = camera_time_us[i] + offset_us; | |
| 172 int64_t clip_timestamp_us = timestamp_aligner.ClipTimestamp( | |
| 173 translated_timestamp_us, system_time_us[i] + kClipBiasUs); | |
| 174 if (translated_timestamp_us <= prev_timestamp_us) { | |
| 175 did_clip = true; | |
| 176 EXPECT_EQ(clip_timestamp_us, | |
| 177 prev_timestamp_us + rtc::kNumMicrosecsPerMillisec); | |
| 178 } else { | |
| 179 // No change from clipping. | |
| 180 EXPECT_EQ(clip_timestamp_us, translated_timestamp_us); | |
| 181 } | |
| 182 prev_timestamp_us = clip_timestamp_us; | |
| 183 } | |
| 184 EXPECT_TRUE(did_clip); | |
| 185 } | |
| 186 | |
| 187 } // namespace rtc | |
| OLD | NEW |
|---|
Chromium Code Reviews
Issue 2877023002:
Move webrtc/{base => rtc_base} (Closed)
