Cast: Provide more meaningful stats.

media/cast/logging/receiver_time_offset_estimator_impl.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_IMPL_H_
+#define MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_IMPL_H_
+
+#include "base/time/time.h"
+#include "base/threading/thread_checker.h"
+#include "media/cast/logging/logging_defines.h"
+#include "media/cast/logging/receiver_time_offset_estimator.h"
+
+namespace media {
+namespace cast {
+
+// This implementation listens to three types of events:
+// 1. kVideoFrameEncoded (sender side)
+// 2. kVideoAckSent (receiver side)
+// 3. kVideoAckReceived (sender side)
+// There is a causal relationship between these events in that these events
+// must happen in order. This class obtains the lower and upper bounds for
+// the offset by taking the difference of timestamps (2) - (1) and (2) - (3),
+// respectively.
+// The bound will become better as the latency between the events decreases.
+class ReceiverTimeOffsetEstimatorImpl : public ReceiverTimeOffsetEstimator {
+ public:
+  ReceiverTimeOffsetEstimatorImpl();
+
+  virtual ~ReceiverTimeOffsetEstimatorImpl();
+
+  // RawEventSubscriber implementations.
+  virtual void OnReceiveFrameEvent(const FrameEvent& frame_event) OVERRIDE;
+  virtual void OnReceivePacketEvent(const PacketEvent& packet_event) OVERRIDE;
+
+  // ReceiverTimeOffsetEstimator implementation.
+  virtual bool GetReceiverOffsetBounds(base::TimeDelta* lower_bound,
+                                       base::TimeDelta* upper_bound) OVERRIDE;
+
+ private:
+  struct EventTimes {
+    base::TimeTicks event_a_time;
+    base::TimeTicks event_b_time;
+    base::TimeTicks event_c_time;
+  };
+
+  typedef std::map<RtpTimestamp, EventTimes> EventTimesMap;
+
+  void UpdateOffsetBounds(const EventTimes& event);
+
+  // Fixed size storage to store event times for recent frames.
+  EventTimesMap event_times_map_;
+
+  bool bounded_;
+  base::TimeDelta offset_lower_bound_;
+  base::TimeDelta offset_upper_bound_;
+
+  base::ThreadChecker thread_checker_;
+  DISALLOW_COPY_AND_ASSIGN(ReceiverTimeOffsetEstimatorImpl);
+};
+
+}  // namespace cast
+}  // namespace media
+
+#endif  // MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_IMPL_H_