Move VP9 frame rate controller to separate class.

Bug: webrtc:9669
Change-Id: I6f30587778e9783182af11d2410464024918e171
Reviewed-on: https://webrtc-review.googlesource.com/96201
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24487}

modules/video_coding/utility/framerate_controller.cc

@@ -0,0 +1,81 @@
+/*
+ *  Copyright (c) 2018 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.
+ */
+
+#include "modules/video_coding/utility/framerate_controller.h"
+
+#include "rtc_base/checks.h"
+
+namespace webrtc {
+
+FramerateController::FramerateController(float target_framerate_fps)
+    : min_frame_interval_ms_(0), framerate_estimator_(1000.0, 1000.0) {
+  SetTargetRate(target_framerate_fps);
+}
+
+void FramerateController::SetTargetRate(float target_framerate_fps) {
+  if (target_framerate_fps_ != target_framerate_fps) {
+    framerate_estimator_.Reset();
+    if (last_timestamp_ms_) {
+      framerate_estimator_.Update(1, *last_timestamp_ms_);
+    }
+
+    const size_t target_frame_interval_ms = 1000 / target_framerate_fps;
+    target_framerate_fps_ = target_framerate_fps;
+    min_frame_interval_ms_ = 85 * target_frame_interval_ms / 100;
+  }
+}
+
+float FramerateController::GetTargetRate() {
+  return *target_framerate_fps_;
+}
+
+void FramerateController::Reset() {
+  framerate_estimator_.Reset();
+  last_timestamp_ms_.reset();
+}
+
+bool FramerateController::DropFrame(uint32_t timestamp_ms) const {
+  if (timestamp_ms < last_timestamp_ms_) {
+    // Timestamp jumps backward. We can't make adequate drop decision. Don't
+    // drop this frame. Stats will be reset in AddFrame().
+    return false;
+  }
+
+  if (Rate(timestamp_ms).value_or(*target_framerate_fps_) >
+      target_framerate_fps_) {
+    return true;
+  }
+
+  if (last_timestamp_ms_) {
+    const int64_t diff_ms =
+        static_cast<int64_t>(timestamp_ms) - *last_timestamp_ms_;
+    if (diff_ms < min_frame_interval_ms_) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+void FramerateController::AddFrame(uint32_t timestamp_ms) {
+  if (timestamp_ms < last_timestamp_ms_) {
+    // Timestamp jumps backward.
+    Reset();
+  }
+
+  framerate_estimator_.Update(1, timestamp_ms);
+  last_timestamp_ms_ = timestamp_ms;
+}
+
+absl::optional<float> FramerateController::Rate(uint32_t timestamp_ms) const {
+  return framerate_estimator_.Rate(timestamp_ms);
+}
+
+}  // namespace webrtc

modules/video_coding/utility/framerate_controller.h

@@ -0,0 +1,44 @@
+/*
+ *  Copyright (c) 2018 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_FRAMERATE_CONTROLLER_H_
+#define MODULES_VIDEO_CODING_UTILITY_FRAMERATE_CONTROLLER_H_
+
+#include "absl/types/optional.h"
+#include "rtc_base/rate_statistics.h"
+
+namespace webrtc {
+
+class FramerateController {
+ public:
+  explicit FramerateController(float target_framerate_fps);
+
+  void SetTargetRate(float target_framerate_fps);
+  float GetTargetRate();
+
+  // Advices user to drop next frame in order to reach target framerate.
+  bool DropFrame(uint32_t timestamp_ms) const;
+
+  void AddFrame(uint32_t timestamp_ms);
+
+  void Reset();
+
+ private:
+  absl::optional<float> Rate(uint32_t timestamp_ms) const;
+
+  absl::optional<float> target_framerate_fps_;
+  absl::optional<uint32_t> last_timestamp_ms_;
+  uint32_t min_frame_interval_ms_;
+  RateStatistics framerate_estimator_;
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_UTILITY_FRAMERATE_CONTROLLER_H_

modules/video_coding/utility/framerate_controller_unittest.cc

@@ -0,0 +1,88 @@
+/*
+ *  Copyright (c) 2018 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.
+ */
+
+#include "modules/video_coding/utility/framerate_controller.h"
+
+#include "test/gtest.h"
+
+namespace webrtc {
+
+TEST(FramerateController, KeepTargetFramerate) {
+  const float input_framerate_fps = 20;
+  const float target_framerate_fps = 5;
+  const float max_abs_framerate_error_fps = target_framerate_fps * 0.1f;
+  const size_t input_duration_secs = 3;
+  const size_t num_input_frames = input_duration_secs * input_framerate_fps;
+
+  FramerateController framerate_controller(target_framerate_fps);
+  size_t num_dropped_frames = 0;
+  for (size_t frame_num = 0; frame_num < num_input_frames; ++frame_num) {
+    const uint32_t timestamp_ms =
+        static_cast<uint32_t>(1000 * frame_num / input_framerate_fps);
+    if (framerate_controller.DropFrame(timestamp_ms)) {
+      ++num_dropped_frames;
+    } else {
+      framerate_controller.AddFrame(timestamp_ms);
+    }
+  }
+
+  const float output_framerate_fps =
+      static_cast<float>(num_input_frames - num_dropped_frames) /
+      input_duration_secs;
+  EXPECT_NEAR(output_framerate_fps, target_framerate_fps,
+              max_abs_framerate_error_fps);
+}
+
+TEST(FramerateController, DoNotDropAnyFramesIfTargerEqualsInput) {
+  const float input_framerate_fps = 30;
+  const size_t input_duration_secs = 3;
+  const size_t num_input_frames = input_duration_secs * input_framerate_fps;
+
+  FramerateController framerate_controller(input_framerate_fps);
+  size_t num_dropped_frames = 0;
+  for (size_t frame_num = 0; frame_num < num_input_frames; ++frame_num) {
+    const uint32_t timestamp_ms =
+        static_cast<uint32_t>(1000 * frame_num / input_framerate_fps);
+    if (framerate_controller.DropFrame(timestamp_ms)) {
+      ++num_dropped_frames;
+    } else {
+      framerate_controller.AddFrame(timestamp_ms);
+    }
+  }
+
+  EXPECT_EQ(num_dropped_frames, 0U);
+}
+
+TEST(FramerateController, DoNotDropFrameWhenTimestampJumpsBackward) {
+  FramerateController framerate_controller(30);
+  ASSERT_FALSE(framerate_controller.DropFrame(66));
+  framerate_controller.AddFrame(66);
+  EXPECT_FALSE(framerate_controller.DropFrame(33));
+}
+
+TEST(FramerateController, DropFrameIfItIsTooCloseToPreviousFrame) {
+  FramerateController framerate_controller(30);
+  ASSERT_FALSE(framerate_controller.DropFrame(33));
+  framerate_controller.AddFrame(33);
+  EXPECT_TRUE(framerate_controller.DropFrame(34));
+}
+
+TEST(FramerateController, FrameDroppingStartsFromSecondInputFrame) {
+  const float input_framerate_fps = 23;
+  const float target_framerate_fps = 19;
+  const uint32_t input_frame_duration_ms =
+      static_cast<uint32_t>(1000 / input_framerate_fps);
+  FramerateController framerate_controller(target_framerate_fps);
+  ASSERT_FALSE(framerate_controller.DropFrame(1 * input_frame_duration_ms));
+  framerate_controller.AddFrame(1 * input_frame_duration_ms);
+  EXPECT_TRUE(framerate_controller.DropFrame(2 * input_frame_duration_ms));
+}
+
+}  // namespace webrtc