blob: 0511da9f3d925e3d9de30362a202dd77be66477d [file] [log] [blame]
// 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.
#include "base/time/time.h"
namespace media {
namespace cast {
// Tracks the jitter and drift between clocks, providing a smoothed offset.
// Internally, a Simple IIR filter is used to maintain a running average that
// moves at a rate based on the passage of time.
class ClockDriftSmoother {
// |time_constant| is the amount of time an impulse signal takes to decay by
// ~62.6%. Interpretation: If the value passed to several Update() calls is
// held constant for T seconds, then the running average will have moved
// towards the value by ~62.6% from where it started.
explicit ClockDriftSmoother(base::TimeDelta time_constant);
// Returns the current offset.
base::TimeDelta Current() const;
// Discard all history and reset to exactly |offset|, measured |now|.
void Reset(base::TimeTicks now, base::TimeDelta offset);
// Update the current offset, which was measured |now|. The weighting that
// |measured_offset| will have on the running average is influenced by how
// much time has passed since the last call to this method (or Reset()).
// |now| should be monotonically non-decreasing over successive calls of this
// method.
void Update(base::TimeTicks now, base::TimeDelta measured_offset);
// Returns a time constant suitable for most use cases, where the clocks
// are expected to drift very little with respect to each other, and the
// jitter caused by clock imprecision is effectively canceled out.
static base::TimeDelta GetDefaultTimeConstant();
const base::TimeDelta time_constant_;
base::TimeTicks last_update_time_;
double estimate_us_;
} // namespace cast
} // namespace media