Implement timestamp translation/filter in VideoCapturer.

webrtc/media/base/videocapturer_unittest.cc

 /*
  *  Copyright (c) 2008 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 <stdio.h>
 
 #include <memory>
 #include <vector>
 
 #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"
 #include "webrtc/media/base/testutils.h"
 #include "webrtc/media/base/videocapturer.h"
 
 using cricket::FakeVideoCapturer;
 
 namespace {
 
@@ skipping 746 matching lines @@
   capturer_->set_enable_camera_list(true);
   capturer_->ConstrainSupportedFormats(vga_format);
   EXPECT_EQ(2u, capturer_->GetSupportedFormats()->size());
   // To make sure it's not just the camera list being broken, add in VGA and
   // try again. This time, only the VGA format should be there.
   supported_formats.push_back(vga_format);
   capturer_->ResetSupportedFormats(supported_formats);
   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);
+  }
+}