Update RateStatistics to handle too-little-data case.

webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.cc

Index: webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.cc
diff --git a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.cc b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.cc
index f38ef783067eb478b27d40837c34ac36f1b2bc43..d391f03262ed270a2ea036417ff70cdb0b436a3d 100644
--- a/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.cc
+++ b/webrtc/modules/remote_bitrate_estimator/remote_bitrate_estimator_single_stream.cc
@@ -44,16 +44,17 @@ struct RemoteBitrateEstimatorSingleStream::Detector {
   OveruseDetector detector;
 };
 
-  RemoteBitrateEstimatorSingleStream::RemoteBitrateEstimatorSingleStream(
-      RemoteBitrateObserver* observer,
-      Clock* clock)
-      : clock_(clock),
-        incoming_bitrate_(kBitrateWindowMs, 8000),
-        remote_rate_(new AimdRateControl()),
-        observer_(observer),
-        crit_sect_(CriticalSectionWrapper::CreateCriticalSection()),
-        last_process_time_(-1),
-        process_interval_ms_(kProcessIntervalMs) {
+RemoteBitrateEstimatorSingleStream::RemoteBitrateEstimatorSingleStream(
+    RemoteBitrateObserver* observer,
+    Clock* clock)
+    : clock_(clock),
+      incoming_bitrate_(kBitrateWindowMs, 8000),
+      last_valid_incoming_bitrate_(0),
+      remote_rate_(new AimdRateControl()),
+      observer_(observer),
+      crit_sect_(CriticalSectionWrapper::CreateCriticalSection()),
+      last_process_time_(-1),
+      process_interval_ms_(kProcessIntervalMs) {
   assert(observer_);
   LOG(LS_INFO) << "RemoteBitrateEstimatorSingleStream: Instantiating.";
 }
@@ -90,7 +91,20 @@ void RemoteBitrateEstimatorSingleStream::IncomingPacket(int64_t arrival_time_ms,
   }
   Detector* estimator = it->second;
   estimator->last_packet_time_ms = now_ms;
+
+  // Check if incoming bitrate estimate is valid, and if it needs to be reset.
+  rtc::Optional<uint32_t> incoming_bitrate = incoming_bitrate_.Rate(now_ms);
+  if (incoming_bitrate) {
+    last_valid_incoming_bitrate_ = *incoming_bitrate;
+  } else if (last_valid_incoming_bitrate_ > 0) {
+    // Incoming bitrate had a previous valid value, but now not enough data
+    // point are left within the current window. Reset incoming bitrate
+    // estimator so that the window size will only contain new data points.
+    incoming_bitrate_.Reset();
+    last_valid_incoming_bitrate_ = 0;
+  }
   incoming_bitrate_.Update(payload_size, now_ms);
+
   const BandwidthUsage prior_state = estimator->detector.State();
   uint32_t timestamp_delta = 0;
   int64_t time_delta = 0;
@@ -106,9 +120,11 @@ void RemoteBitrateEstimatorSingleStream::IncomingPacket(int64_t arrival_time_ms,
                                estimator->estimator.num_of_deltas(), now_ms);
   }
   if (estimator->detector.State() == kBwOverusing) {
-    uint32_t incoming_bitrate_bps = incoming_bitrate_.Rate(now_ms);
-    if (prior_state != kBwOverusing ||
-        remote_rate_->TimeToReduceFurther(now_ms, incoming_bitrate_bps)) {
+    rtc::Optional<uint32_t> incoming_bitrate_bps =
+        incoming_bitrate_.Rate(now_ms);
+    if (incoming_bitrate_bps &&
+        (prior_state != kBwOverusing ||
+         remote_rate_->TimeToReduceFurther(now_ms, *incoming_bitrate_bps))) {
       // The first overuse should immediately trigger a new estimate.
       // We also have to update the estimate immediately if we are overusing
       // and the target bitrate is too high compared to what we are receiving.
@@ -167,6 +183,7 @@ void RemoteBitrateEstimatorSingleStream::UpdateEstimate(int64_t now_ms) {
     remote_rate_.reset(new AimdRateControl());
     return;
   }
+
   double mean_noise_var = sum_var_noise /
       static_cast<double>(overuse_detectors_.size());
   const RateControlInput input(bw_state,