Enable the bayesian bitrate estimator by default.

webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc

 /*
  *  Copyright (c) 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.
  */
 
@@ skipping 101 matching lines @@
     IncomingFeedback(now_ms, send_time_ms, seq_num++, 1000, kPacingInfo1);
   }
 
   EXPECT_TRUE(bitrate_observer_.updated());
   EXPECT_NEAR(bitrate_observer_.latest_bitrate(), 4000000u, 10000u);
 }
 
 TEST_F(DelayBasedBweTest, GetProbingInterval) {
   int64_t default_interval_ms = bitrate_estimator_->GetProbingIntervalMs();
   EXPECT_GT(default_interval_ms, 0);
-  CapacityDropTestHelper(1, true, 567, 0);
+  CapacityDropTestHelper(1, true, 333, 0);

[terelius, 2017/03/17 13:34:07]

It would be nice to know why the send bitrate drops faster with the new
estimator. (Assuming it doesn't take too long to figure out.)

[stefan-webrtc, 2017/03/30 07:26:48]

I added some logging to see what happens:

109819 Sample: 920.106689 Uncertainty: 0.735696
109819 Bitrate: 914.338196, variance: 0.491732
109962 Sample: 856.960022 Uncertainty: 0.627538
109962 Bitrate: 860.799255, variance: 0.367454
110000 Dropping capacity to 500 kbps
110118 Sample: 593.706665 Uncertainty: 3.102844
110118 Bitrate: 765.194214, variance: 3.446188
110277 Sample: 529.066650 Uncertainty: 3.085851
110277 Bitrate: 654.202271, variance: 4.476050
110427 Sample: 493.600006 Uncertainty: 2.454933
110427 Bitrate: 556.034180, variance: 3.683817
110333 BWE below 500 kbps: 472629
110561 Sample: 466.399994 Uncertainty: 1.612027
110561 Bitrate: 487.044983, variance: 2.000100
110718 Sample: 525.333313 Uncertainty: 0.786135

to me this looks like what we expect. It takes us 3 updates before we fully
trust this new metric, and the reason for that is the increased uncertainty
right after the drop, but the uncertainty is reduced after a few updates. One
could argue that we should tune it to not adapt this quickly, but I think this
is the case mostly because this being just a factor of 2 decrease. Had it been a
factor of 5 or 10 it would have been a different story.

The old estimator used a fixed window of 1 second, so that didn't have any
possibility of getting below 500 kbps this quickly.

I do think there's room for some more tuning here though, and I think one
interesting factor we haven't accounted for is the difference between send
bitrate and the BWE. Our measurement could be considered more reliable if the
send bitrate is close to the BWE, while if it's a lot lower then the acked
bitrate will not correspond to the actual bandwidth of the pipe.

   int64_t interval_ms = bitrate_estimator_->GetProbingIntervalMs();
   EXPECT_GT(interval_ms, 0);
   EXPECT_NE(interval_ms, default_interval_ms);
 }
 
 TEST_F(DelayBasedBweTest, InitialBehavior) {
   InitialBehaviorTestHelper(674840);
 }
 
 TEST_F(DelayBasedBweTest, RateIncreaseReordering) {
   RateIncreaseReorderingTestHelper(674840);
 }
 
 TEST_F(DelayBasedBweTest, RateIncreaseRtpTimestamps) {
-  RateIncreaseRtpTimestampsTestHelper(1240);
+  RateIncreaseRtpTimestampsTestHelper(1288);
 }
 
 TEST_F(DelayBasedBweTest, CapacityDropOneStream) {
-  CapacityDropTestHelper(1, false, 567, 0);
+  CapacityDropTestHelper(1, false, 333, 0);
 }
 
 TEST_F(DelayBasedBweTest, CapacityDropPosOffsetChange) {
-  CapacityDropTestHelper(1, false, 200, 30000);
+  CapacityDropTestHelper(1, false, 300, 30000);
 }
 
 TEST_F(DelayBasedBweTest, CapacityDropNegOffsetChange) {
-  CapacityDropTestHelper(1, false, 733, -30000);
+  CapacityDropTestHelper(1, false, 300, -30000);
 }
 
 TEST_F(DelayBasedBweTest, CapacityDropOneStreamWrap) {
-  CapacityDropTestHelper(1, true, 567, 0);
+  CapacityDropTestHelper(1, true, 333, 0);
 }
 
 TEST_F(DelayBasedBweTest, TestTimestampGrouping) {
   TestTimestampGroupingTestHelper();
 }
 
 TEST_F(DelayBasedBweTest, TestShortTimeoutAndWrap) {
   // Simulate a client leaving and rejoining the call after 35 seconds. This
   // will make abs send time wrap, so if streams aren't timed out properly
   // the next 30 seconds of packets will be out of order.
   TestWrappingHelper(35);
 }
 
 TEST_F(DelayBasedBweTest, TestLongTimeoutAndWrap) {
   // Simulate a client leaving and rejoining the call after some multiple of
   // 64 seconds later. This will cause a zero difference in abs send times due
   // to the wrap, but a big difference in arrival time, if streams aren't
   // properly timed out.
   TestWrappingHelper(10 * 64);
 }
 
 class DelayBasedBweExperimentTest : public DelayBasedBweTest {

[terelius, 2017/03/17 13:34:08]

Could we remove this class?

There is also a reference to "WebRTC-ImprovedBitrateEstimate" in
webrtc/sdk/objc/Framework/Classes/RTCFieldTrials.mm
Clean up now or later?

[stefan-webrtc, 2017/03/30 07:26:48]

Done.

  public:
   DelayBasedBweExperimentTest()
       : override_field_trials_("WebRTC-ImprovedBitrateEstimate/Enabled/") {
     bitrate_estimator_.reset(new DelayBasedBwe(nullptr, &clock_));
   }
 
  private:
   test::ScopedFieldTrials override_field_trials_;
 };
 
@@ skipping 22 matching lines @@
   DelayBasedBweTrendlineExperimentTest()
       : override_field_trials_("WebRTC-BweTrendlineFilter/Enabled-15,0.9,4/") {
     bitrate_estimator_.reset(new DelayBasedBwe(nullptr, &clock_));
   }
 
  private:
   test::ScopedFieldTrials override_field_trials_;
 };
 
 TEST_F(DelayBasedBweTrendlineExperimentTest, RateIncreaseRtpTimestamps) {
-  RateIncreaseRtpTimestampsTestHelper(1240);
+  RateIncreaseRtpTimestampsTestHelper(1288);
 }
 
 TEST_F(DelayBasedBweTrendlineExperimentTest, CapacityDropOneStream) {
-  CapacityDropTestHelper(1, false, 600, 0);
+  CapacityDropTestHelper(1, false, 433, 0);
 }
 
 TEST_F(DelayBasedBweTrendlineExperimentTest, CapacityDropPosOffsetChange) {
   CapacityDropTestHelper(1, false, 600, 30000);
 }
 
 TEST_F(DelayBasedBweTrendlineExperimentTest, CapacityDropNegOffsetChange) {
-  CapacityDropTestHelper(1, false, 1267, -30000);
+  CapacityDropTestHelper(1, false, 767, -30000);
 }
 
 TEST_F(DelayBasedBweTrendlineExperimentTest, CapacityDropOneStreamWrap) {
-  CapacityDropTestHelper(1, true, 600, 0);
+  CapacityDropTestHelper(1, true, 433, 0);
 }
 
 class DelayBasedBweMedianSlopeExperimentTest : public DelayBasedBweTest {
  public:
   DelayBasedBweMedianSlopeExperimentTest()
       : override_field_trials_("WebRTC-BweMedianSlopeFilter/Enabled-20,4/") {
     bitrate_estimator_.reset(new DelayBasedBwe(nullptr, &clock_));
   }
 
  private:
   test::ScopedFieldTrials override_field_trials_;
 };
 
 TEST_F(DelayBasedBweMedianSlopeExperimentTest, RateIncreaseRtpTimestamps) {
-  RateIncreaseRtpTimestampsTestHelper(1240);
+  RateIncreaseRtpTimestampsTestHelper(1288);
 }
 
 TEST_F(DelayBasedBweMedianSlopeExperimentTest, CapacityDropOneStream) {
-  CapacityDropTestHelper(1, false, 600, 0);
+  CapacityDropTestHelper(1, false, 367, 0);
 }
 
 TEST_F(DelayBasedBweMedianSlopeExperimentTest, CapacityDropPosOffsetChange) {
   CapacityDropTestHelper(1, false, 600, 30000);
 }
 
 TEST_F(DelayBasedBweMedianSlopeExperimentTest, CapacityDropNegOffsetChange) {
-  CapacityDropTestHelper(1, false, 1267, -30000);
+  CapacityDropTestHelper(1, false, 767, -30000);
 }
 
 TEST_F(DelayBasedBweMedianSlopeExperimentTest, CapacityDropOneStreamWrap) {
-  CapacityDropTestHelper(1, true, 600, 0);
+  CapacityDropTestHelper(1, true, 367, 0);
 }
 
 }  // namespace webrtc