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_|.
+  //
+  // |max_time| is typically the media timestamp of the last audio frame
+  // buffered by the audio hardware.
+  void SetTime(base::TimeDelta current_time, base::TimeDelta max_time);

[acolwell GONE FROM CHROMIUM, 2014/07/09 00:42:46]

s/SetTime/SetInterpolationRange/ , s/SetTime/SetBounds/ or something like that.
ISTM it is better to think of this in terms of start and end points of the
interpolation instead of using the old clock concepts.

[scherkus (not reviewing), 2014/07/09 01:54:32]

Agreed -- done.

+
+  // Sets the upper bound used for interpolation. Note that if |max_time| is
+  // less than what was previously set via SetTime(), then all future calls
+  // to GetInterpolatedTime() will return |max_time|.
+  void SetMaxTime(base::TimeDelta max_time);

[acolwell GONE FROM CHROMIUM, 2014/07/09 00:42:46]

s/SetMaxTime/SetUpperBound/ since that is what the description says.

[scherkus (not reviewing), 2014/07/09 01:54:32]

Done.

+
+  // Computes an interpolated time based on SetTime().
+  base::TimeDelta GetInterpolatedTime();
+
+ private:
+  // Updates the reference points based on the current calculated time.
+  void UpdateReferencePoints();
+
+  // Updates the reference points based on the given |current_time|.
+  void UpdateReferencePoints(base::TimeDelta current_time);
+
+  // Returns the time elapsed based on the current reference points, ignoring
+  // the |max_time_| cap.
+  base::TimeDelta EstimatedElapsedTime();
+
+  // Translates |time| into the current media time, based on the perspective of
+  // the monotonically-increasing system clock.
+  base::TimeDelta ElapsedViaProvidedTime(const base::TimeTicks& time) const;
+
+  base::TimeDelta ClampToValidTimeRange(base::TimeDelta time) const;
+
+  base::TickClock* const tick_clock_;
+
+  bool interpolating_;
+
+  // Whether the clock is stalled because it has reached the |max_time_|
+  // allowed.
+  bool underflow_;
+
+  // The monotonic system clock time when this Clock last started playing or had
+  // its time set via SetTime().
+  base::TimeTicks reference_;
+
+  // Current accumulated amount of media time.  The remaining portion must be
+  // calculated by comparing the system time to the reference time.
+  base::TimeDelta media_time_;

[acolwell GONE FROM CHROMIUM, 2014/07/09 00:42:46]

nit: s/media_time_/lower_bound_/?

[scherkus (not reviewing), 2014/07/09 01:54:32]

Done.

+
+  // Current playback rate.
+  float playback_rate_;
+
+  // The maximum time that can be returned by calls to Elapsed().
+  base::TimeDelta max_time_;

[acolwell GONE FROM CHROMIUM, 2014/07/09 00:42:46]

nit: s/max_time_/upper_bound_/?

[scherkus (not reviewing), 2014/07/09 01:54:32]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(TimeDeltaInterpolator);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_TIME_DELTA_INTERPOLATOR_H_