Don't reset quality scaler on resolution change.

webrtc/video/vie_encoder.cc

 /*
  *  Copyright (c) 2012 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 445 matching lines @@
       std::move(streams), encoder_config_.min_transmit_bitrate_bps);
 
   ConfigureQualityScaler();
 }
 
 void ViEEncoder::ConfigureQualityScaler() {
   RTC_DCHECK_RUN_ON(&encoder_queue_);
   const auto scaling_settings = settings_.encoder->GetScalingSettings();
   const bool degradation_preference_allows_scaling =
       degradation_preference_ != DegradationPreference::kMaintainResolution;
-  if (degradation_preference_allows_scaling && scaling_settings.enabled) {
+
+  stats_proxy_->SetResolutionRestrictionStats(
+      degradation_preference_allows_scaling, scale_counter_[kCpu] > 0,
+      scale_counter_[kQuality]);
+
+  if (degradation_preference_allows_scaling &&
+      scaling_settings.enabled) {
+    // Abort if quality scaler has already been configured.
+    if (quality_scaler_.get() != nullptr)
+      return;
     // Drop frames and scale down until desired quality is achieved.
     if (scaling_settings.thresholds) {
       quality_scaler_.reset(
           new QualityScaler(this, *(scaling_settings.thresholds)));
     } else {
       quality_scaler_.reset(new QualityScaler(this, codec_type_));
     }
   } else {
     quality_scaler_.reset(nullptr);
     initial_rampup_ = kMaxInitialFramedrop;
   }
-  stats_proxy_->SetResolutionRestrictionStats(
-      degradation_preference_allows_scaling, scale_counter_[kCpu] > 0,
-      scale_counter_[kQuality]);
 }
 
 void ViEEncoder::OnFrame(const VideoFrame& video_frame) {
   RTC_DCHECK_RUNS_SERIALIZED(&incoming_frame_race_checker_);
   VideoFrame incoming_frame = video_frame;
 
   // Local time in webrtc time base.
   int64_t current_time_us = clock_->TimeInMicroseconds();
   int64_t current_time_ms = current_time_us / rtc::kNumMicrosecsPerMillisec;
   // TODO(nisse): This always overrides the incoming timestamp. Don't
@@ skipping 318 matching lines @@
   --scale_counter_[reason];
   source_proxy_->RequestHigherResolutionThan(current_pixel_count);
   LOG(LS_INFO) << "Scaling up resolution.";
   for (size_t i = 0; i < kScaleReasonSize; ++i) {
     LOG(LS_INFO) << "Scaled " << scale_counter_[i]
                  << " times for reason: " << (i ? "cpu" : "quality");
   }
 }
 
 }  // namespace webrtc