1 files changed, 207 insertions, 0 deletions
diff --git a/third_party/libwebrtc/rtc_base/timestamp_aligner_unittest.cc b/third_party/libwebrtc/rtc_base/timestamp_aligner_unittest.cc
new file mode 100644
index 0000000000..ca91b62625
--- /dev/null
+++ b/third_party/libwebrtc/rtc_base/timestamp_aligner_unittest.cc
@@ -0,0 +1,207 @@
+/*
+ *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "rtc_base/timestamp_aligner.h"
+
+#include <math.h>
+
+#include <algorithm>
+#include <limits>
+
+#include "rtc_base/random.h"
+#include "rtc_base/time_utils.h"
+#include "test/gtest.h"
+
+namespace rtc {
+
+namespace {
+// Computes the difference x_k - mean(x), when x_k is the linear sequence x_k =
+// k, and the "mean" is plain mean for the first `window_size` samples, followed
+// by exponential averaging with weight 1 / `window_size` for each new sample.
+// This is needed to predict the effect of camera clock drift on the timestamp
+// translation. See the comment on TimestampAligner::UpdateOffset for more
+// context.
+double MeanTimeDifference(int nsamples, int window_size) {
+  if (nsamples <= window_size) {
+    // Plain averaging.
+    return nsamples / 2.0;
+  } else {
+    // Exponential convergence towards
+    // interval_error * (window_size - 1)
+    double alpha = 1.0 - 1.0 / window_size;
+
+    return ((window_size - 1) -
+            (window_size / 2.0 - 1) * pow(alpha, nsamples - window_size));
+  }
+}
+
+class TimestampAlignerForTest : public TimestampAligner {
+  // Make internal methods accessible to testing.
+ public:
+  using TimestampAligner::ClipTimestamp;
+  using TimestampAligner::UpdateOffset;
+};
+
+void TestTimestampFilter(double rel_freq_error) {
+  TimestampAlignerForTest timestamp_aligner_for_test;
+  TimestampAligner timestamp_aligner;
+  const int64_t kEpoch = 10000;
+  const int64_t kJitterUs = 5000;
+  const int64_t kIntervalUs = 33333;  // 30 FPS
+  const int kWindowSize = 100;
+  const int kNumFrames = 3 * kWindowSize;
+
+  int64_t interval_error_us = kIntervalUs * rel_freq_error;
+  int64_t system_start_us = rtc::TimeMicros();
+  webrtc::Random random(17);
+
+  int64_t prev_translated_time_us = system_start_us;
+
+  for (int i = 0; i < kNumFrames; i++) {
+    // Camera time subject to drift.
+    int64_t camera_time_us = kEpoch + i * (kIntervalUs + interval_error_us);
+    int64_t system_time_us = system_start_us + i * kIntervalUs;
+    // And system time readings are subject to jitter.
+    int64_t system_measured_us = system_time_us + random.Rand(kJitterUs);
+
+    int64_t offset_us = timestamp_aligner_for_test.UpdateOffset(
+        camera_time_us, system_measured_us);
+
+    int64_t filtered_time_us = camera_time_us + offset_us;
+    int64_t translated_time_us = timestamp_aligner_for_test.ClipTimestamp(
+        filtered_time_us, system_measured_us);
+
+    // Check that we get identical result from the all-in-one helper method.
+    ASSERT_EQ(translated_time_us, timestamp_aligner.TranslateTimestamp(
+                                      camera_time_us, system_measured_us));
+
+    EXPECT_LE(translated_time_us, system_measured_us);
+    EXPECT_GE(translated_time_us,
+              prev_translated_time_us + rtc::kNumMicrosecsPerMillisec);
+
+    // The relative frequency error contributes to the expected error
+    // by a factor which is the difference between the current time
+    // and the average of earlier sample times.
+    int64_t expected_error_us =
+        kJitterUs / 2 +
+        rel_freq_error * kIntervalUs * MeanTimeDifference(i, kWindowSize);
+
+    int64_t bias_us = filtered_time_us - translated_time_us;
+    EXPECT_GE(bias_us, 0);
+
+    if (i == 0) {
+      EXPECT_EQ(translated_time_us, system_measured_us);
+    } else {
+      EXPECT_NEAR(filtered_time_us, system_time_us + expected_error_us,
+                  2.0 * kJitterUs / sqrt(std::max(i, kWindowSize)));
+    }
+    // If the camera clock runs too fast (rel_freq_error > 0.0), The
+    // bias is expected to roughly cancel the expected error from the
+    // clock drift, as this grows. Otherwise, it reflects the
+    // measurement noise. The tolerances here were selected after some
+    // trial and error.
+    if (i < 10 || rel_freq_error <= 0.0) {
+      EXPECT_LE(bias_us, 3000);
+    } else {
+      EXPECT_NEAR(bias_us, expected_error_us, 1500);
+    }
+    prev_translated_time_us = translated_time_us;
+  }
+}
+
+}  // Anonymous namespace
+
+TEST(TimestampAlignerTest, AttenuateTimestampJitterNoDrift) {
+  TestTimestampFilter(0.0);
+}
+
+// 100 ppm is a worst case for a reasonable crystal.
+TEST(TimestampAlignerTest, AttenuateTimestampJitterSmallPosDrift) {
+  TestTimestampFilter(0.0001);
+}
+
+TEST(TimestampAlignerTest, AttenuateTimestampJitterSmallNegDrift) {
+  TestTimestampFilter(-0.0001);
+}
+
+// 3000 ppm, 3 ms / s, is the worst observed drift, see
+// https://bugs.chromium.org/p/webrtc/issues/detail?id=5456
+TEST(TimestampAlignerTest, AttenuateTimestampJitterLargePosDrift) {
+  TestTimestampFilter(0.003);
+}
+
+TEST(TimestampAlignerTest, AttenuateTimestampJitterLargeNegDrift) {
+  TestTimestampFilter(-0.003);
+}
+
+// Exhibits a mostly hypothetical problem, where certain inputs to the
+// TimestampAligner.UpdateOffset filter result in non-monotonous
+// translated timestamps. This test verifies that the ClipTimestamp
+// logic handles this case correctly.
+TEST(TimestampAlignerTest, ClipToMonotonous) {
+  TimestampAlignerForTest timestamp_aligner;
+
+  // For system time stamps { 0, s1, s1 + s2 }, and camera timestamps
+  // {0, c1, c1 + c2}, we exhibit non-monotonous behaviour if and only
+  // if c1 > s1 + 2 s2 + 4 c2.
+  const int kNumSamples = 3;
+  const int64_t kCaptureTimeUs[kNumSamples] = {0, 80000, 90001};
+  const int64_t kSystemTimeUs[kNumSamples] = {0, 10000, 20000};
+  const int64_t expected_offset_us[kNumSamples] = {0, -35000, -46667};
+
+  // Non-monotonic translated timestamps can happen when only for
+  // translated timestamps in the future. Which is tolerated if
+  // `timestamp_aligner.clip_bias_us` is large enough. Instead of
+  // changing that private member for this test, just add the bias to
+  // `kSystemTimeUs` when calling ClipTimestamp.
+  const int64_t kClipBiasUs = 100000;
+
+  bool did_clip = false;
+  int64_t prev_timestamp_us = std::numeric_limits<int64_t>::min();
+  for (int i = 0; i < kNumSamples; i++) {
+    int64_t offset_us =
+        timestamp_aligner.UpdateOffset(kCaptureTimeUs[i], kSystemTimeUs[i]);
+    EXPECT_EQ(offset_us, expected_offset_us[i]);
+
+    int64_t translated_timestamp_us = kCaptureTimeUs[i] + offset_us;
+    int64_t clip_timestamp_us = timestamp_aligner.ClipTimestamp(
+        translated_timestamp_us, kSystemTimeUs[i] + kClipBiasUs);
+    if (translated_timestamp_us <= prev_timestamp_us) {
+      did_clip = true;
+      EXPECT_EQ(clip_timestamp_us,
+                prev_timestamp_us + rtc::kNumMicrosecsPerMillisec);
+    } else {
+      // No change from clipping.
+      EXPECT_EQ(clip_timestamp_us, translated_timestamp_us);
+    }
+    prev_timestamp_us = clip_timestamp_us;
+  }
+  EXPECT_TRUE(did_clip);
+}
+
+TEST(TimestampAlignerTest, TranslateTimestampWithoutStateUpdate) {
+  TimestampAligner timestamp_aligner;
+
+  constexpr int kNumSamples = 4;
+  constexpr int64_t kCaptureTimeUs[kNumSamples] = {0, 80000, 90001, 100000};
+  constexpr int64_t kSystemTimeUs[kNumSamples] = {0, 10000, 20000, 30000};
+  constexpr int64_t kQueryCaptureTimeOffsetUs[kNumSamples] = {0, 123, -321,
+                                                              345};
+
+  for (int i = 0; i < kNumSamples; i++) {
+    int64_t reference_timestamp = timestamp_aligner.TranslateTimestamp(
+        kCaptureTimeUs[i], kSystemTimeUs[i]);
+    EXPECT_EQ(reference_timestamp - kQueryCaptureTimeOffsetUs[i],
+              timestamp_aligner.TranslateTimestamp(
+                  kCaptureTimeUs[i] - kQueryCaptureTimeOffsetUs[i]));
+  }
+}
+
+}  // namespace rtc