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_ = 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 = (now - last_update_time_).InMicroseconds(); 43 last_update_time_ = now; 44 const double weight = 45 elapsed_us / (elapsed_us + time_constant_.InMicroseconds()); 46 estimate_us_ = weight * measured_offset.InMicroseconds() + 47 (1.0 - weight) * estimate_us_; 48 } 49 } 50 51 // static 52 base::TimeDelta ClockDriftSmoother::GetDefaultTimeConstant() { 53 static const int kDefaultTimeConstantInSeconds = 30; 54 return base::TimeDelta::FromSeconds(kDefaultTimeConstantInSeconds); 55 } 56 57 } // namespace cast 58 } // namespace media 59
