Enable the bayesian bitrate estimator by default.

webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc

Index: webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc
diff --git a/webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc b/webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc
index 559179e5180936e57c208be550273439a8d15c5b..60d5c0997f659d0354793079bc9e6af8e1a3a1a2 100644
--- a/webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc
+++ b/webrtc/modules/congestion_controller/delay_based_bwe_unittest.cc
@@ -119,7 +119,7 @@ TEST_F(DelayBasedBweTest, ProbeDetectionSlowerArrivalHighBitrate) {
 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);
@@ -134,23 +134,23 @@ TEST_F(DelayBasedBweTest, RateIncreaseReordering) {
 }
 
 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) {
@@ -215,11 +215,11 @@ class DelayBasedBweTrendlineExperimentTest : public DelayBasedBweTest {
 };
 
 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) {
@@ -227,11 +227,11 @@ TEST_F(DelayBasedBweTrendlineExperimentTest, CapacityDropPosOffsetChange) {
 }
 
 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 {
@@ -246,11 +246,11 @@ class DelayBasedBweMedianSlopeExperimentTest : public DelayBasedBweTest {
 };
 
 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) {
@@ -258,11 +258,11 @@ TEST_F(DelayBasedBweMedianSlopeExperimentTest, CapacityDropPosOffsetChange) {
 }
 
 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