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diff --git a/third_party/libwebrtc/modules/video_coding/utility/quality_scaler.h b/third_party/libwebrtc/modules/video_coding/utility/quality_scaler.h
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+/*
+ *  Copyright (c) 2014 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.
+ */
+
+#ifndef MODULES_VIDEO_CODING_UTILITY_QUALITY_SCALER_H_
+#define MODULES_VIDEO_CODING_UTILITY_QUALITY_SCALER_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <memory>
+
+#include "absl/types/optional.h"
+#include "api/field_trials_view.h"
+#include "api/scoped_refptr.h"
+#include "api/sequence_checker.h"
+#include "api/video_codecs/video_encoder.h"
+#include "rtc_base/experiments/quality_scaling_experiment.h"
+#include "rtc_base/numerics/moving_average.h"
+#include "rtc_base/ref_count.h"
+#include "rtc_base/system/no_unique_address.h"
+
+namespace webrtc {
+
+class QualityScalerQpUsageHandlerCallbackInterface;
+class QualityScalerQpUsageHandlerInterface;
+
+// QualityScaler runs asynchronously and monitors QP values of encoded frames.
+// It holds a reference to a QualityScalerQpUsageHandlerInterface implementation
+// to signal an overuse or underuse of QP (which indicate a desire to scale the
+// video stream down or up).
+class QualityScaler {
+ public:
+  // Construct a QualityScaler with given `thresholds` and `handler`.
+  // This starts the quality scaler periodically checking what the average QP
+  // has been recently.
+  QualityScaler(QualityScalerQpUsageHandlerInterface* handler,
+                VideoEncoder::QpThresholds thresholds,
+                const FieldTrialsView& field_trials);
+  virtual ~QualityScaler();
+  // Should be called each time a frame is dropped at encoding.
+  void ReportDroppedFrameByMediaOpt();
+  void ReportDroppedFrameByEncoder();
+  // Inform the QualityScaler of the last seen QP.
+  void ReportQp(int qp, int64_t time_sent_us);
+
+  void SetQpThresholds(VideoEncoder::QpThresholds thresholds);
+  bool QpFastFilterLow() const;
+
+  // The following members declared protected for testing purposes.
+ protected:
+  QualityScaler(QualityScalerQpUsageHandlerInterface* handler,
+                VideoEncoder::QpThresholds thresholds,
+                const FieldTrialsView& field_trials,
+                int64_t sampling_period_ms);
+
+ private:
+  class QpSmoother;
+  class CheckQpTask;
+  class CheckQpTaskHandlerCallback;
+
+  enum class CheckQpResult {
+    kInsufficientSamples,
+    kNormalQp,
+    kHighQp,
+    kLowQp,
+  };
+
+  // Starts checking for QP in a delayed task. When the resulting CheckQpTask
+  // completes, it will invoke this method again, ensuring that we always
+  // periodically check for QP. See CheckQpTask for more details. We never run
+  // more than one CheckQpTask at a time.
+  void StartNextCheckQpTask();
+
+  CheckQpResult CheckQp() const;
+  void ClearSamples();
+
+  std::unique_ptr<CheckQpTask> pending_qp_task_ RTC_GUARDED_BY(&task_checker_);
+  QualityScalerQpUsageHandlerInterface* const handler_
+      RTC_GUARDED_BY(&task_checker_);
+  RTC_NO_UNIQUE_ADDRESS SequenceChecker task_checker_;
+
+  VideoEncoder::QpThresholds thresholds_ RTC_GUARDED_BY(&task_checker_);
+  const int64_t sampling_period_ms_;
+  bool fast_rampup_ RTC_GUARDED_BY(&task_checker_);
+  rtc::MovingAverage average_qp_ RTC_GUARDED_BY(&task_checker_);
+  rtc::MovingAverage framedrop_percent_media_opt_
+      RTC_GUARDED_BY(&task_checker_);
+  rtc::MovingAverage framedrop_percent_all_ RTC_GUARDED_BY(&task_checker_);
+
+  // Used by QualityScalingExperiment.
+  const bool experiment_enabled_;
+  QualityScalingExperiment::Config config_ RTC_GUARDED_BY(&task_checker_);
+  std::unique_ptr<QpSmoother> qp_smoother_high_ RTC_GUARDED_BY(&task_checker_);
+  std::unique_ptr<QpSmoother> qp_smoother_low_ RTC_GUARDED_BY(&task_checker_);
+
+  const size_t min_frames_needed_;
+  const double initial_scale_factor_;
+  const absl::optional<double> scale_factor_;
+};
+
+// Reacts to QP being too high or too low. For best quality, when QP is high it
+// is desired to decrease the resolution or frame rate of the stream and when QP
+// is low it is desired to increase the resolution or frame rate of the stream.
+// Whether to reconfigure the stream is ultimately up to the handler, which is
+// able to respond asynchronously.
+class QualityScalerQpUsageHandlerInterface {
+ public:
+  virtual ~QualityScalerQpUsageHandlerInterface();
+
+  virtual void OnReportQpUsageHigh() = 0;
+  virtual void OnReportQpUsageLow() = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_UTILITY_QUALITY_SCALER_H_