Implemented a proper clock for audio/video synchronization.

media/base/clock_impl.cc

+// Copyright (c) 2009 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 "base/logging.h"
+#include "media/base/clock_impl.h"
+
+namespace media {
+
+ClockImpl::ClockImpl(TimeProvider* time_provider)
+    : time_provider_(time_provider),
+      playing_(false),
+      playback_rate_(1.0f) {
+}
+
+ClockImpl::~ClockImpl() {
+}
+
+base::TimeDelta ClockImpl::Play() {
+  DCHECK(!playing_);
+  reference_ = time_provider_();
+  playing_ = true;
+  return media_time_;
+}
+
+base::TimeDelta ClockImpl::Pause() {
+  DCHECK(playing_);
+  // Save our new accumulated amount of media time.
+  media_time_ = Elapsed();
+  playing_ = false;
+  return media_time_;
+}
+
+void ClockImpl::SetTime(const base::TimeDelta& time) {
+  if (playing_) {
+    reference_ = time_provider_();
+  }
+  media_time_ = time;
+}
+
+void ClockImpl::SetPlaybackRate(float playback_rate) {
+  if (playing_) {
+    base::Time time = time_provider_();
+    media_time_ = ElapsedViaProvidedTime(time);
+    reference_ = time;
+  }
+  playback_rate_ = playback_rate;
+}
+
+base::TimeDelta ClockImpl::Elapsed() const {
+  if (!playing_) {
+    return media_time_;
+  }
+  return ElapsedViaProvidedTime(time_provider_());
+}
+
+base::TimeDelta ClockImpl::ElapsedViaProvidedTime(
+    const base::Time& time) const {
+  // TODO(scherkus): floating point badness scaling time by playback rate.
+  int64 now_us = (time - reference_).InMicroseconds();
+  now_us = static_cast<int64>(now_us * playback_rate_);
+  return media_time_ + base::TimeDelta::FromMicroseconds(now_us);
+}
+
+}  // namespace media