Make the BWE threshold adaptive.

webrtc/modules/remote_bitrate_estimator/overuse_detector.cc

Index: webrtc/modules/remote_bitrate_estimator/overuse_detector.cc
diff --git a/webrtc/modules/remote_bitrate_estimator/overuse_detector.cc b/webrtc/modules/remote_bitrate_estimator/overuse_detector.cc
index 33b234c1f3aee2d962fe301a58cf8ec225af5750..3c29b3529855d97ff776106bef3eca246f93db3a 100644
--- a/webrtc/modules/remote_bitrate_estimator/overuse_detector.cc
+++ b/webrtc/modules/remote_bitrate_estimator/overuse_detector.cc
@@ -11,25 +11,51 @@
 #include "webrtc/modules/remote_bitrate_estimator/overuse_detector.h"
 
 #include <algorithm>
+#include <sstream>
 #include <math.h>
 #include <stdlib.h>
 
+#include "webrtc/base/checks.h"
+#include "webrtc/base/common.h"
 #include "webrtc/modules/remote_bitrate_estimator/include/bwe_defines.h"
 #include "webrtc/modules/remote_bitrate_estimator/test/bwe_test_logging.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_utility.h"
+#include "webrtc/system_wrappers/interface/field_trial.h"
 #include "webrtc/system_wrappers/interface/trace.h"
 
 namespace webrtc {
 
-enum { kOverUsingTimeThreshold = 100 };
+const char* kAdaptiveThresholdExperiment = "WebRTC-AdaptiveBweThreshold";
+const char* kEnabledPrefix = "Enabled";
+const size_t kEnabledPrefixLength = sizeof(kEnabledPrefix) - 1;
+const size_t kMinExperimentLength = kEnabledPrefixLength + 3;
+
+const double kMaxAdaptOffsetMs = 15.0;
+const double kOverUsingTimeThreshold = 10;
+
+bool AdaptiveThresholdExperimentIsEnabled() {
+  std::string experiment_string =
+      webrtc::field_trial::FindFullName(kAdaptiveThresholdExperiment);
+  if (experiment_string.length() < kMinExperimentLength)
+    return false;
+  return experiment_string.substr(0, kEnabledPrefixLength) == kEnabledPrefix;
+}
 
 OveruseDetector::OveruseDetector(const OverUseDetectorOptions& options)
-    : options_(options),
-      threshold_(options_.initial_threshold),
+    : in_experiment_(AdaptiveThresholdExperimentIsEnabled()),
+      k_up_(0.01),
+      k_down_(0.00018),
+      overusing_time_threshold_(100),
+      options_(options),
+      threshold_(12.5),
+      last_update_ms_(-1),
       prev_offset_(0.0),
       time_over_using_(-1),
       overuse_counter_(0),
-      hypothesis_(kBwNormal) {}
+      hypothesis_(kBwNormal) {
+  if (in_experiment_)
+    InitializeExperiment();
+}
 
 OveruseDetector::~OveruseDetector() {}
 
@@ -37,21 +63,6 @@ BandwidthUsage OveruseDetector::State() const {
   return hypothesis_;
 }
 
-
-void OveruseDetector::SetRateControlRegion(RateControlRegion region) {
-  switch (region) {
-    case kRcMaxUnknown: {
-      threshold_ = options_.initial_threshold;
-      break;
-    }
-    case kRcAboveMax:
-    case kRcNearMax: {
-      threshold_ = options_.initial_threshold / 2;
-      break;
-    }
-  }
-}
-
 BandwidthUsage OveruseDetector::Detect(double offset,
                                        double ts_delta,
                                        int num_of_deltas,
@@ -64,7 +75,6 @@ BandwidthUsage OveruseDetector::Detect(double offset,
   const double T = std::min(num_of_deltas, 60) * offset;
   BWE_TEST_LOGGING_PLOT(1, "offset", now_ms, T);
   BWE_TEST_LOGGING_PLOT(1, "threshold", now_ms, threshold_);
-
   if (T > threshold_) {
     if (time_over_using_ == -1) {
       // Initialize the timer. Assume that we've been
@@ -93,6 +103,62 @@ BandwidthUsage OveruseDetector::Detect(double offset,
     overuse_counter_ = 0;
     hypothesis_ = kBwNormal;
   }
+
+  UpdateThreshold(T, now_ms);
+
   return hypothesis_;
 }
+
+void OveruseDetector::UpdateThreshold(double modified_offset, int64_t now_ms) {
+  if (!in_experiment_)
+    return;
+
+  if (last_update_ms_ == -1)
+    last_update_ms_ = now_ms;
+
+  if (fabs(modified_offset) > threshold_ + kMaxAdaptOffsetMs) {
+    // Avoid adapting the threshold to big latency spikes, caused e.g.,
+    // by a sudden capacity drop.
+    last_update_ms_ = now_ms;
+    return;
+  }
+
+  const double k = fabs(modified_offset) < threshold_ ? k_down_ : k_up_;
+  threshold_ +=
+      k * (fabs(modified_offset) - threshold_) * (now_ms - last_update_ms_);
+
+  const double kMinThreshold = 6;
+  const double kMaxThreshold = 600;
+  threshold_ = std::min(std::max(threshold_, kMinThreshold), kMaxThreshold);
+
+  last_update_ms_ = now_ms;
+}
+
+// Gets thresholds from the experiment name following the format
+// "WebRTC-AdaptiveBweThreshold/Enabled-0.5,0.002/".
+void OveruseDetector::InitializeExperiment() {
+  DCHECK(in_experiment_);

[pbos-webrtc, 2015/07/06 13:30:17]

If this is now the only place where in_experiment_ is actually used, remove it
and do if (AdaptiveThresh...Enabled()) InitializeExperiment(); in ctor.

+  double k_up = 0.0;
+  double k_down = 0.0;
+  overusing_time_threshold_ = kOverUsingTimeThreshold;
+  if (ReadExperimentConstants(&k_up, &k_down)) {
+    k_up_ = k_up;
+    k_down_ = k_down;
+  }
+}
+
+bool OveruseDetector::ReadExperimentConstants(double* k_up,
+                                              double* k_down) const {
+  std::string experiment_string =
+      webrtc::field_trial::FindFullName(kAdaptiveThresholdExperiment);
+  std::stringstream ss(experiment_string.substr(kEnabledPrefixLength + 1));

[pbos-webrtc, 2015/07/06 13:30:17]

Easier to do this?
  return sscanf(experiment_string.c_str(), "%d,%d", k_up, k_down) == 2;

It won't complain on invalid strings ("Experiment-0.2,0.5-yolo$wag49"), but it
should still parse the correct string safely. I don't think we have to protect
for incorrect strings accidentally being read, we should just not crash on
anything and I think this does it. :)

(Please also test locally that it works.)

+  ss >> *k_up;
+  if (ss.peek() != ',')
+    return false;
+  ss.ignore();
+  ss >> *k_down;
+  if (ss.rdbuf()->in_avail() > 0)
+    return false;
+  return true;
+}
 }  // namespace webrtc