Implement timestamp translation/filter in VideoCapturer.

webrtc/media/base/videocapturer_unittest.cc

Index: webrtc/media/base/videocapturer_unittest.cc
diff --git a/webrtc/media/base/videocapturer_unittest.cc b/webrtc/media/base/videocapturer_unittest.cc
index 25230b5118a80517ff861d5bb473019f58528332..73f99af8b707e75d3eae6d7f4652ed7cc084d017 100644
--- a/webrtc/media/base/videocapturer_unittest.cc
+++ b/webrtc/media/base/videocapturer_unittest.cc
@@ -15,6 +15,7 @@
 
 #include "webrtc/base/gunit.h"
 #include "webrtc/base/logging.h"
+#include "webrtc/base/random.h"
 #include "webrtc/base/thread.h"
 #include "webrtc/media/base/fakevideocapturer.h"
 #include "webrtc/media/base/fakevideorenderer.h"
@@ -781,3 +782,90 @@ TEST_F(VideoCapturerTest, BlacklistAllFormats) {
   ASSERT_EQ(1u, capturer_->GetSupportedFormats()->size());
   EXPECT_EQ(vga_format.height, capturer_->GetSupportedFormats()->at(0).height);
 }
+
+TEST_F(VideoCapturerTest, AttenuateTimestampJitter) {
+  const int kWidth = 800;
+  const int kHeight = 400;
+
+  const double rel_freq_error = 0.001;
+  const int64_t epoch = 10000;
+  const int64_t jitter_us = 5000;
+  const int64_t interval_us = 33333; // 30 FPS
+  const int64_t interval_error_us = interval_us * rel_freq_error;
+  const int nframes = 200;
+
+  const int64_t system_start_us = rtc::TimeMicros();
+  webrtc::Random random(17);
+
+  for (int i = 0; i < nframes; i++) {
+    // Camera time subject to drift.
+    int64_t camera_time_us = epoch + i * (interval_us + interval_error_us);
+    int64_t system_time_us = system_start_us + i * interval_us;
+    // And system time readings are subject to jitter.
+    int64_t system_measured_us = system_time_us + random.Rand(jitter_us);
+
+    int out_width;
+    int out_height;
+    int crop_width;
+    int crop_height;
+    int crop_x;
+    int crop_y;
+    int64_t translated_time_us;
+
+    EXPECT_TRUE(capturer_->AdaptFrame(kWidth, kHeight,
+                                      camera_time_us, system_measured_us,
+                                      &out_width, &out_height,
+                                      &crop_width, &crop_height,
+                                      &crop_x, &crop_y, &translated_time_us));
+
+    // 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. This expression is
+    // accurate as long as we do plain averaging (i.e, for the first
+    // 100 frames), after which it converges exponentially to the
+    // limit of interval_us * (window_size - 1).
+    int64_t expected_error_us = jitter_us / 2 +
+                                rel_freq_error * i * interval_us / 2;
+
+    if (i == 0) {
+      EXPECT_EQ(translated_time_us, system_measured_us);
+    } else {
+      EXPECT_NEAR(translated_time_us, system_time_us + expected_error_us,
+                  2.0 * jitter_us / sqrt(std::max(i, 100)));
+    }
+  }
+}
+
+TEST_F(VideoCapturerTest, TimestampTranslationBypass) {
+  const int kWidth = 800;
+  const int kHeight = 400;
+
+  const int64_t jitter_us = 10000;
+  const int64_t interval_us = 33333; // 30 FPS
+  const int nframes = 50;
+
+  const int64_t system_start_us = rtc::TimeMicros();
+  webrtc::Random random(17);
+
+  for (int i = 0; i < nframes; i++) {
+    // Camera time and system time are the same, but we read the
+    // system time a few ms later.
+    int64_t camera_time_us = system_start_us + i * interval_us;
+    int64_t system_measured_us = camera_time_us + random.Rand(jitter_us);
+
+    int out_width;
+    int out_height;
+    int crop_width;
+    int crop_height;
+    int crop_x;
+    int crop_y;
+    int64_t translated_time_us;
+
+    EXPECT_TRUE(capturer_->AdaptFrame(kWidth, kHeight,
+                                      camera_time_us, system_measured_us,
+                                      &out_width, &out_height,
+                                      &crop_width, &crop_height,
+                                      &crop_x, &crop_y, &translated_time_us));
+    EXPECT_EQ(camera_time_us, translated_time_us);
+  }
+}