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diff --git a/third_party/libwebrtc/video/frame_cadence_adapter.h b/third_party/libwebrtc/video/frame_cadence_adapter.h
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+/*
+ *  Copyright (c) 2021 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 VIDEO_FRAME_CADENCE_ADAPTER_H_
+#define VIDEO_FRAME_CADENCE_ADAPTER_H_
+
+#include <memory>
+
+#include "absl/base/attributes.h"
+#include "api/field_trials_view.h"
+#include "api/task_queue/task_queue_base.h"
+#include "api/units/time_delta.h"
+#include "api/video/video_frame.h"
+#include "api/video/video_sink_interface.h"
+#include "rtc_base/synchronization/mutex.h"
+#include "rtc_base/thread_annotations.h"
+#include "system_wrappers/include/clock.h"
+
+namespace webrtc {
+
+// A sink adapter implementing mutations to the received frame cadence.
+// With the exception of the constructor and the methods overridden in
+// VideoSinkInterface, the rest of the interface to this class (including dtor)
+// needs to happen on the queue passed in Create.
+class FrameCadenceAdapterInterface
+    : public rtc::VideoSinkInterface<VideoFrame> {
+ public:
+  // Averaging window spanning 90 frames at default 30fps, matching old media
+  // optimization module defaults.
+  // TODO(crbug.com/1255737): Use TimeDelta.
+  static constexpr int64_t kFrameRateAveragingWindowSizeMs = (1000 / 30) * 90;
+  // In zero-hertz mode, the idle repeat rate is a compromise between
+  // RTP receiver keyframe-requesting timeout (3s), other backend limitations
+  // and some worst case RTT.
+  static constexpr TimeDelta kZeroHertzIdleRepeatRatePeriod =
+      TimeDelta::Millis(1000);
+  // The number of frame periods to wait for new frames until starting to
+  // request refresh frames.
+  static constexpr int kOnDiscardedFrameRefreshFramePeriod = 3;
+
+  struct ZeroHertzModeParams {
+    // The number of simulcast layers used in this configuration.
+    size_t num_simulcast_layers = 0;
+  };
+
+  // Callback interface used to inform instance owners.
+  class Callback {
+   public:
+    virtual ~Callback() = default;
+
+    // Called when a frame arrives on the |queue| specified in Create.
+    //
+    // The |post_time| parameter indicates the current time sampled when
+    // FrameCadenceAdapterInterface::OnFrame was called.
+    //
+    // |frames_scheduled_for_processing| indicates how many frames that have
+    // been scheduled for processing. During sequential conditions where
+    // FrameCadenceAdapterInterface::OnFrame is invoked and subsequently ending
+    // up in this callback, this value will read 1. Otherwise if the
+    // |queue| gets stalled for some reason, the value will increase
+    // beyond 1.
+    virtual void OnFrame(Timestamp post_time,
+                         int frames_scheduled_for_processing,
+                         const VideoFrame& frame) = 0;
+
+    // Called when the source has discarded a frame.
+    virtual void OnDiscardedFrame() = 0;
+
+    // Called when the adapter needs the source to send a refresh frame.
+    virtual void RequestRefreshFrame() = 0;
+  };
+
+  // Factory function creating a production instance. Deletion of the returned
+  // instance needs to happen on the same sequence that Create() was called on.
+  // Frames arriving in FrameCadenceAdapterInterface::OnFrame are posted to
+  // Callback::OnFrame on the |queue|.
+  static std::unique_ptr<FrameCadenceAdapterInterface> Create(
+      Clock* clock,
+      TaskQueueBase* queue,
+      const FieldTrialsView& field_trials);
+
+  // Call before using the rest of the API.
+  virtual void Initialize(Callback* callback) = 0;
+
+  // Pass zero hertz parameters in |params| as a prerequisite to enable
+  // zero-hertz operation. If absl:::nullopt is passed, the cadence adapter will
+  // switch to passthrough mode.
+  virtual void SetZeroHertzModeEnabled(
+      absl::optional<ZeroHertzModeParams> params) = 0;
+
+  // Returns the input framerate. This is measured by RateStatistics when
+  // zero-hertz mode is off, and returns the max framerate in zero-hertz mode.
+  virtual absl::optional<uint32_t> GetInputFrameRateFps() = 0;
+
+  // Updates frame rate. This is done unconditionally irrespective of adapter
+  // mode.
+  virtual void UpdateFrameRate() = 0;
+
+  // Updates quality convergence status for an enabled spatial layer.
+  // Convergence means QP has dropped to a low-enough level to warrant ceasing
+  // to send identical frames at high frequency.
+  virtual void UpdateLayerQualityConvergence(size_t spatial_index,
+                                             bool converged) = 0;
+
+  // Updates spatial layer enabled status.
+  virtual void UpdateLayerStatus(size_t spatial_index, bool enabled) = 0;
+
+  // Conditionally requests a refresh frame via
+  // Callback::RequestRefreshFrame.
+  virtual void ProcessKeyFrameRequest() = 0;
+};
+
+}  // namespace webrtc
+
+#endif  // VIDEO_FRAME_CADENCE_ADAPTER_H_