media/cast/logging/receiver_time_offset_estimator_impl.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_IMPL_H_
   6 #define MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_IMPL_H_
   7
   8 #include <map>
   9
  10 #include "base/time/time.h"
  11 #include "base/threading/thread_checker.h"
  12 #include "media/cast/common/mod_util.h"
  13 #include "media/cast/logging/logging_defines.h"
  14 #include "media/cast/logging/receiver_time_offset_estimator.h"
  15
  16 namespace media {
  17 namespace cast {
  18
  19
  20 // This should be large enough so that we can collect all 3 events before
  21 // the entry gets removed from the map.
  22 const size_t kMaxEventTimesMapSize = 500;
  23
  24 // The lower, this is, the faster we adjust to clock drift.
  25 // (But with more jitter.)
  26 const size_t kClockDriftSpeed = 500;
  27
  28
  29 // This implementation listens to two pair of events
  30 // 1. FRAME_ACK_SENT / FRAME_ACK_RECEIVED  (receiver->sender)
  31 // 2. PACKET_SENT_TO_NETWORK / PACKET_RECEIVED (sender->receiver)
  32 // There is a causal relationship between these events in that these events
  33 // must happen in order. This class obtains the lower and upper bounds for
  34 // the offset by taking the difference of timestamps.
  35 class ReceiverTimeOffsetEstimatorImpl : public ReceiverTimeOffsetEstimator {
  36  public:
  37   ReceiverTimeOffsetEstimatorImpl();
  38
  39   ~ReceiverTimeOffsetEstimatorImpl() final;
  40
  41   // RawEventSubscriber implementations.
  42   void OnReceiveFrameEvent(const FrameEvent& frame_event) final;
  43   void OnReceivePacketEvent(const PacketEvent& packet_event) final;
  44
  45   // ReceiverTimeOffsetEstimator implementation.
  46   bool GetReceiverOffsetBounds(base::TimeDelta* lower_bound,
  47                                base::TimeDelta* upper_bound) final;
  48
  49  private:
  50   // This helper uses the difference between sent and recived event
  51   // to calculate an upper bound on the difference between the clocks
  52   // on the sender and receiver. Note that this difference can take
  53   // very large positive or negative values, but the smaller value is
  54   // always the better estimate, since a receive event cannot possibly
  55   // happen before a send event.  Note that we use this to calculate
  56   // both upper and lower bounds by reversing the sender/receiver
  57   // relationship.
  58   class BoundCalculator {
  59    public:
  60     typedef std::pair<base::TimeTicks, base::TimeTicks> TimeTickPair;
  61     typedef std::map<uint64, TimeTickPair> EventMap;
  62
  63     BoundCalculator();
  64     ~BoundCalculator();
  65     bool has_bound() const { return has_bound_; }
  66     base::TimeDelta bound() const { return bound_; }
  67
  68     void SetSent(uint32 rtp,
  69                  uint32 packet_id,
  70                  bool audio,
  71                  base::TimeTicks t);
  72
  73     void SetReceived(uint32 rtp,
  74                      uint16 packet_id,
  75                      bool audio,
  76                      base::TimeTicks t);
  77
  78    private:
  79     void UpdateBound(base::TimeTicks a, base::TimeTicks b);
  80     void CheckUpdate(uint64 key);
  81
  82    private:
  83     EventMap events_;
  84     bool has_bound_;
  85     base::TimeDelta bound_;
  86   };
  87
  88   // Fixed size storage to store event times for recent frames.
  89   BoundCalculator upper_bound_;
  90   BoundCalculator lower_bound_;
  91
  92   base::ThreadChecker thread_checker_;
  93   DISALLOW_COPY_AND_ASSIGN(ReceiverTimeOffsetEstimatorImpl);
  94 };
  95
  96 }  // namespace cast
  97 }  // namespace media
  98
  99 #endif  // MEDIA_CAST_LOGGING_RECEIVER_TIME_OFFSET_ESTIMATOR_IMPL_H_