frame_rate_estimator.h

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/*

 *  Copyright (c) 2019 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 COMMON_VIDEO_FRAME_RATE_ESTIMATOR_H_

#define COMMON_VIDEO_FRAME_RATE_ESTIMATOR_H_

#include <deque>

#include "absl/types/optional.h"

#include "api/units/time_delta.h"

#include "api/units/timestamp.h"

namespace webrtc {

// Class used to estimate a frame-rate using inter-frame intervals.

// Some notes on usage:

// This class is intended to accurately estimate the frame rate during a

// continuous stream. Unlike a traditional rate estimator that looks at number

// of data points within a time window, if the input stops this implementation

// will not smoothly fall down towards 0. This is done so that the estimated

// fps is not affected by edge conditions like if we sample just before or just

// after the next frame.

// To avoid problems if a stream is stopped and restarted (where estimated fps

// could look too low), users of this class should explicitly call Reset() on

// restart.

// Also note that this class is not thread safe, it's up to the user to guard

// against concurrent access.

class FrameRateEstimator {

 public:

  explicit FrameRateEstimator(TimeDelta averaging_window);

  // Insert a frame, potentially culling old frames that falls outside the

  // averaging window.

  void OnFrame(Timestamp time);

  // Get the current average FPS, based on the frames currently in the window.

  absl::optional<double> GetAverageFps() const;

  // Move the window so it ends at `now`, and return the new fps estimate.

  absl::optional<double> GetAverageFps(Timestamp now);

  // Completely clear the averaging window.

  void Reset();

 private:

  void CullOld(Timestamp now);

  const TimeDelta averaging_window_;

  std::deque<Timestamp> frame_times_;

};

}  // namespace webrtc

#endif  // COMMON_VIDEO_FRAME_RATE_ESTIMATOR_H_