Relanding "Pass time constant to bwe smoothing filter."

webrtc/modules/congestion_controller/probing_interval_estimator.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.
  */
 
 #include "webrtc/modules/congestion_controller/probing_interval_estimator.h"
 
 #include <algorithm>
 #include <utility>
 
 namespace webrtc {
 
 namespace {
 constexpr int kMinIntervalMs = 2000;
+constexpr int kDefaultIntervalMs = 3000;
 constexpr int kMaxIntervalMs = 50000;
 }
 
 ProbingIntervalEstimator::ProbingIntervalEstimator(
     const AimdRateControl* aimd_rate_control)
     : ProbingIntervalEstimator(kMinIntervalMs,
                                kMaxIntervalMs,
+                               kDefaultIntervalMs,
                                aimd_rate_control) {}
 
 ProbingIntervalEstimator::ProbingIntervalEstimator(
-    int min_interval_ms,
-    int max_interval_ms,
+    int64_t min_interval_ms,
+    int64_t max_interval_ms,
+    int64_t default_interval_ms,
     const AimdRateControl* aimd_rate_control)
     : min_interval_ms_(min_interval_ms),
       max_interval_ms_(max_interval_ms),
+      default_interval_ms_(default_interval_ms),
       aimd_rate_control_(aimd_rate_control) {}
 
-rtc::Optional<int> ProbingIntervalEstimator::GetIntervalMs() const {
+int64_t ProbingIntervalEstimator::GetIntervalMs() const {
   rtc::Optional<int> bitrate_drop =
       aimd_rate_control_->GetLastBitrateDecreaseBps();
   int increase_rate = aimd_rate_control_->GetNearMaxIncreaseRateBps();
 
   if (!bitrate_drop || increase_rate <= 0)
-    return rtc::Optional<int>();
+    return default_interval_ms_;
 
-  return rtc::Optional<int>(std::min(
+  return std::min(
       max_interval_ms_,
-      std::max(1000 * (*bitrate_drop) / increase_rate, min_interval_ms_)));
+      std::max(static_cast<int64_t>(1000 * (*bitrate_drop) / increase_rate),
+               min_interval_ms_));
 }
 
 }  // namespace webrtc