[Cast] Repair receiver playout time calculations and frame skip logic.

media/cast/base/clock_drift_smoother.cc

+// Copyright 2014 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/cast/base/clock_drift_smoother.h"
+
+#include "base/logging.h"
+
+namespace media {
+namespace cast {
+
+ClockDriftSmoother::ClockDriftSmoother(base::TimeDelta time_constant)
+    : time_constant_(time_constant),
+      estimate_us_(0.0) {
+  DCHECK(time_constant_ > base::TimeDelta());
+}
+
+ClockDriftSmoother::~ClockDriftSmoother() {}
+
+base::TimeDelta ClockDriftSmoother::Current() const {
+  DCHECK(!last_update_time_.is_null());
+  return base::TimeDelta::FromMicroseconds(
+      static_cast<int64>(estimate_us_ + 0.5));  // Round to nearest microsecond.
+}
+
+void ClockDriftSmoother::Reset(base::TimeTicks now,
+                               base::TimeDelta measured_offset) {
+  DCHECK(!now.is_null());
+  last_update_time_ = now;
+  estimate_us_ = measured_offset.InMicroseconds();
+}
+
+void ClockDriftSmoother::Update(base::TimeTicks now,
+                                base::TimeDelta measured_offset) {
+  DCHECK(!now.is_null());
+  if (last_update_time_.is_null()) {
+    Reset(now, measured_offset);
+  } else if (now < last_update_time_) {
+    // |now| is not monotonically non-decreasing.
+    NOTREACHED();
+  } else {
+    const double elapsed_us = (now - last_update_time_).InMicroseconds();
+    last_update_time_ = now;
+    const double weight =
+        elapsed_us / (elapsed_us + time_constant_.InMicroseconds());
+    estimate_us_ = weight * measured_offset.InMicroseconds() +
+        (1.0 - weight) * estimate_us_;
+  }
+}
+
+// static
+base::TimeDelta ClockDriftSmoother::GetDefaultTimeConstant() {
+  static const int kDefaultTimeConstantInSeconds = 30;
+  return base::TimeDelta::FromSeconds(kDefaultTimeConstantInSeconds);
+}
+
+}  // namespace cast
+}  // namespace media