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// 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 <stddef.h>
#include <stdint.h>
#include <map>
#include "base/macros.h"
#include "base/threading/thread_checker.h"
#include "base/time/time.h"
#include "media/cast/common/mod_util.h"
#include "media/cast/logging/logging_defines.h"
#include "media/cast/logging/receiver_time_offset_estimator.h"
namespace media {
namespace cast {
// This should be large enough so that we can collect all 3 events before
// the entry gets removed from the map.
const size_t kMaxEventTimesMapSize = 500;
// The lower, this is, the faster we adjust to clock drift.
// (But with more jitter.)
const size_t kClockDriftSpeed = 500;
// This implementation listens to two pair of events
// 1. FRAME_ACK_SENT / FRAME_ACK_RECEIVED (receiver->sender)
// 2. PACKET_SENT_TO_NETWORK / PACKET_RECEIVED (sender->receiver)
// 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.
class ReceiverTimeOffsetEstimatorImpl : public ReceiverTimeOffsetEstimator {
public:
ReceiverTimeOffsetEstimatorImpl();
~ReceiverTimeOffsetEstimatorImpl() final;
// RawEventSubscriber implementations.
void OnReceiveFrameEvent(const FrameEvent& frame_event) final;
void OnReceivePacketEvent(const PacketEvent& packet_event) final;
// ReceiverTimeOffsetEstimator implementation.
bool GetReceiverOffsetBounds(base::TimeDelta* lower_bound,
base::TimeDelta* upper_bound) final;
private:
// This helper uses the difference between sent and recived event
// to calculate an upper bound on the difference between the clocks
// on the sender and receiver. Note that this difference can take
// very large positive or negative values, but the smaller value is
// always the better estimate, since a receive event cannot possibly
// happen before a send event. Note that we use this to calculate
// both upper and lower bounds by reversing the sender/receiver
// relationship.
class BoundCalculator {
public:
typedef std::pair<base::TimeTicks, base::TimeTicks> TimeTickPair;
typedef std::map<uint64_t, TimeTickPair> EventMap;
BoundCalculator();
~BoundCalculator();
bool has_bound() const { return has_bound_; }
base::TimeDelta bound() const { return bound_; }
void SetSent(RtpTimeTicks rtp,
uint16_t packet_id,
bool audio,
base::TimeTicks t);
void SetReceived(RtpTimeTicks rtp,
uint16_t packet_id,
bool audio,
base::TimeTicks t);
private:
void UpdateBound(base::TimeTicks a, base::TimeTicks b);
void CheckUpdate(uint64_t key);
private:
EventMap events_;
bool has_bound_;
base::TimeDelta bound_;
};
// Fixed size storage to store event times for recent frames.
BoundCalculator upper_bound_;
BoundCalculator lower_bound_;
base::ThreadChecker thread_checker_;
DISALLOW_COPY_AND_ASSIGN(ReceiverTimeOffsetEstimatorImpl);
};
} // namespace cast
} // namespace media
#endif // MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_IMPL_H_
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