media/cast/common/clock_drift_smoother.cc

   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 #include "media/cast/common/clock_drift_smoother.h"
   6
   7 #include "base/logging.h"
   8
   9 namespace media {
  10 namespace cast {
  11
  12 ClockDriftSmoother::ClockDriftSmoother(base::TimeDelta time_constant)
  13     : time_constant_(time_constant),
  14       estimate_us_(0.0) {
  15   DCHECK(time_constant_ > base::TimeDelta());
  16 }
  17
  18 ClockDriftSmoother::~ClockDriftSmoother() {}
  19
  20 base::TimeDelta ClockDriftSmoother::Current() const {
  21   DCHECK(!last_update_time_.is_null());
  22   return base::TimeDelta::FromMicroseconds(
  23       static_cast<int64>(estimate_us_ + 0.5));  // Round to nearest microsecond.
  24 }
  25
  26 void ClockDriftSmoother::Reset(base::TimeTicks now,
  27                                base::TimeDelta measured_offset) {
  28   DCHECK(!now.is_null());
  29   last_update_time_ = now;
  30   estimate_us_ = static_cast<double>(measured_offset.InMicroseconds());
  31 }
  32
  33 void ClockDriftSmoother::Update(base::TimeTicks now,
  34                                 base::TimeDelta measured_offset) {
  35   DCHECK(!now.is_null());
  36   if (last_update_time_.is_null()) {
  37     Reset(now, measured_offset);
  38   } else if (now < last_update_time_) {
  39     // |now| is not monotonically non-decreasing.
  40     NOTREACHED();
  41   } else {
  42     const double elapsed_us =
  43         static_cast<double>((now - last_update_time_).InMicroseconds());
  44     last_update_time_ = now;
  45     const double weight =
  46         elapsed_us / (elapsed_us + time_constant_.InMicroseconds());
  47     estimate_us_ = weight * measured_offset.InMicroseconds() +
  48         (1.0 - weight) * estimate_us_;
  49   }
  50 }
  51
  52 // static
  53 base::TimeDelta ClockDriftSmoother::GetDefaultTimeConstant() {
  54   static const int kDefaultTimeConstantInSeconds = 30;
  55   return base::TimeDelta::FromSeconds(kDefaultTimeConstantInSeconds);
  56 }
  57
  58 }  // namespace cast
  59 }  // namespace media