Rename media::Clock to media::TimeDeltaInterpolator and update API.

media/base/time_delta_interpolator.h

+// Copyright (c) 2012 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.
+
+#ifndef MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_
+#define MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_
+
+#include "base/basictypes.h"
+#include "base/time/time.h"
+#include "media/base/media_export.h"
+
+namespace base {
+class TickClock;
+}  // namespace base
+
+namespace media {
+
+// Interpolates between two TimeDeltas based on the passage of wall clock time
+// and the current playback rate.
+//
+// TimeDeltaInterpolator is not thread-safe and must be externally locked.
+class MEDIA_EXPORT TimeDeltaInterpolator {
+ public:
+  // Constructs an interpolator initialized to zero with a rate of 1.0.
+  //
+  // |tick_clock| is used for sampling wall clock time for interpolating.
+  explicit TimeDeltaInterpolator(base::TickClock* tick_clock);
+  ~TimeDeltaInterpolator();
+
+  bool interpolating() { return interpolating_; }
+
+  // Starts returning interpolated TimeDelta values.
+  //
+  // |tick_clock| will be queried for a new reference time value.
+  base::TimeDelta StartInterpolating();
+
+  // Stops returning interpolated TimeDelta values.
+  //
+  // |tick_clock| will be queried for a new reference time value.
+  base::TimeDelta StopInterpolating();
+
+  // Sets a new rate at which to interpolate.
+  //
+  // |tick_clock| will be queried for a new reference time value.
+  void SetPlaybackRate(float playback_rate);
+
+  // Sets the two timestamps to interpolate between at |playback_rate_|.
+  // |upper_bound| must be greater or equal to |lower_bound|.
+  //
+  // |upper_bound| is typically the media timestamp of the last audio frame
+  // buffered by the audio hardware.
+  void SetBounds(base::TimeDelta lower_bound, base::TimeDelta upper_bound);
+
+  // Sets the upper bound used for interpolation. Note that if |upper_bound| is
+  // less than what was previously set via SetTime(), then all future calls
+  // to GetInterpolatedTime() will return |upper_bound|.
+  void SetUpperBound(base::TimeDelta upper_bound);
+
+  // Computes an interpolated time based on SetTime().
+  base::TimeDelta GetInterpolatedTime();
+
+ private:
+  base::TickClock* const tick_clock_;
+
+  bool interpolating_;
+
+  // The range of time to interpolate between.
+  base::TimeDelta lower_bound_;
+  base::TimeDelta upper_bound_;
+
+  // The monotonic system clock time used for interpolating between
+  // |lower_bound_| and |upper_bound_|.
+  base::TimeTicks reference_;
+
+  float playback_rate_;
+
+  DISALLOW_COPY_AND_ASSIGN(TimeDeltaInterpolator);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_