Introduce cadence based VideoRendererAlgorithm.

media/base/moving_average.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "media/base/moving_average.h"
+
+#include <algorithm>
+
+namespace media {
+
+MovingAverage::MovingAverage(size_t depth)
+    : depth_(depth), count_(0), samples_(depth_) {
+}
+
+MovingAverage::~MovingAverage() {
+}
+
+void MovingAverage::AddSample(base::TimeDelta sample) {
+  // |samples_| is zero-initialized, so |oldest| is also zero before |count_|
+  // exceeds |depth_|.
+  base::TimeDelta& oldest = samples_[count_++ % depth_];
+  total_ += sample - oldest;
+  oldest = sample;
+}
+
+base::TimeDelta MovingAverage::Average() const {
+  DCHECK_GT(count_, 0u);
+
+  // TODO(dalecurtis): Consider limiting |depth| to powers of two so that we can
+  // replace the integer divide with a bit shift operation.
+
+  return total_ / std::min(depth_, count_);
+}
+
+void MovingAverage::Reset() {
+  count_ = 0;
+  total_ = base::TimeDelta();
+  std::fill(samples_.begin(), samples_.end(), base::TimeDelta());
+}
+
+}  // namespace media