Cast: Provide more meaningful stats.

media/cast/logging/receiver_time_offset_estimator.h

+// 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.
+
+#ifndef MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_H_
+#define MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_H_
+
+#include "base/time/time.h"
+#include "media/cast/logging/raw_event_subscriber.h"
+
+namespace media {
+namespace cast {
+
+// Estimates receiver time offset based on raw events received.
+// In most cases, the sender and receiver run on different time lines.
+// In order to convert receiver time back to sender time (or vice versa)
+// a certain time offset has to be applied.
+// An implementation of this interface listens to raw events to figure out
+// the bounds for the offset value (assuming the true offset value is constant
+// over the lifetime of a cast session).
+// The offset values provided here should be used as follows:
+// - Convert from sender to receiver time: add offset value to sender timestamp.
+// - Convert from receiver to sender time: subtract offset value from receiver
+//   timestamp.
+class ReceiverTimeOffsetEstimator : public RawEventSubscriber {
+ public:
+  virtual ~ReceiverTimeOffsetEstimator() {}
+
+  // If bounds are known, assigns |lower_bound| and |upper_bound| with the
+  // lower bound and upper bound for the offset value, respectively.
+  // Returns true if bounds are known.
+  virtual bool GetReceiverOffsetBounds(base::TimeDelta* lower_bound,
+                                       base::TimeDelta* upper_bound) = 0;
+};
+
+}  // namespace cast
+}  // namespace media
+
+#endif  // MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_H_