Bitrate controller for VideoToolbox encoder.

webrtc/modules/video_coding/include/bitrate_adjuster.h

+/*
+ *  Copyright 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.
+ */
+
+#ifndef WEBRTC_MODULES_VIDEO_CODING_INCLUDE_BITRATE_ADJUSTER_H_
+#define WEBRTC_MODULES_VIDEO_CODING_INCLUDE_BITRATE_ADJUSTER_H_
+
+#include <functional>
+
+#include "webrtc/base/criticalsection.h"
+#include "webrtc/base/rollingaccumulator.h"
+
+namespace webrtc {
+
+class BitrateAdjusterObserver {
+ public:
+  virtual ~BitrateAdjusterObserver() {}
+
+  // Called when a new bitrate adjustment is computed.
+  virtual void OnBitrateAdjusted(uint32_t adjusted_bitrate_kbit) = 0;
+};
+
+// Certain hardware encoders tend to consistently overshoot the bitrate that
+// they are configured to encode at. This class estimates an adjusted bitrate
+// that when set on the encoder will produce the desired bitrate.
+class BitrateAdjuster {
+ public:
+  // The observer is called each time a new bitrate adjustment is computed.
+  explicit BitrateAdjuster(BitrateAdjusterObserver* observer);
+  virtual ~BitrateAdjuster() {}
+
+  // Sets the desired bitrate in kbps. Should be called at least once before
+  // Update.
+  void SetTargetBitrate(uint32_t bitrate_kbit);
+  uint32_t GetTargetBitrate() const;
+
+  // Returns the adjusted bitrate in kbps.
+  uint32_t GetAdjustedBitrate() const;
+
+  // This should be called after each frame is encoded. The timestamp at which
+  // it is called is used to estimate the output bitrate of the encoder.
+  // Should be called from only one thread.
+  void Update(size_t frame_size);
+
+ private:
+  static const uint32_t kBitrateUpdateIntervalMs;
+  static const uint32_t kBitrateTolerancePct;
+
+  void Reset();
+  void UpdateBitrate(uint32_t current_time_ms);
+  void UpdateBitrateTracker(size_t frame_size, uint32_t current_time_ms);
+
+  rtc::CriticalSection crit_;
+  BitrateAdjusterObserver* observer_;
+  // The bitrate we want.
+  volatile uint32_t target_bitrate_kbit_ GUARDED_BY(crit_);
+  // The bitrate we use to get what we want.
+  volatile uint32_t adjusted_bitrate_kbit_ GUARDED_BY(crit_);
+  // Used to estimate bitrate.
+  rtc::RollingAccumulator<float> bitrate_tracker_ GUARDED_BY(crit_);
+  // The last time we tried to adjust the bitrate.
+  uint32_t last_bitrate_update_time_ms_ GUARDED_BY(crit_);
+  // The timestamp of the last time Update was called.
+  uint32_t last_update_time_ms_ GUARDED_BY(crit_);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_VIDEO_CODING_INCLUDE_BITRATE_ADJUSTER_H_