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/*
* Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "modules/audio_processing/aec3/clockdrift_detector.h"
namespace webrtc {
ClockdriftDetector::ClockdriftDetector()
: level_(Level::kNone), stability_counter_(0) {
delay_history_.fill(0);
}
ClockdriftDetector::~ClockdriftDetector() = default;
void ClockdriftDetector::Update(int delay_estimate) {
if (delay_estimate == delay_history_[0]) {
// Reset clockdrift level if delay estimate is stable for 7500 blocks (30
// seconds).
if (++stability_counter_ > 7500)
level_ = Level::kNone;
return;
}
stability_counter_ = 0;
const int d1 = delay_history_[0] - delay_estimate;
const int d2 = delay_history_[1] - delay_estimate;
const int d3 = delay_history_[2] - delay_estimate;
// Patterns recognized as positive clockdrift:
// [x-3], x-2, x-1, x.
// [x-3], x-1, x-2, x.
const bool probable_drift_up =
(d1 == -1 && d2 == -2) || (d1 == -2 && d2 == -1);
const bool drift_up = probable_drift_up && d3 == -3;
// Patterns recognized as negative clockdrift:
// [x+3], x+2, x+1, x.
// [x+3], x+1, x+2, x.
const bool probable_drift_down = (d1 == 1 && d2 == 2) || (d1 == 2 && d2 == 1);
const bool drift_down = probable_drift_down && d3 == 3;
// Set clockdrift level.
if (drift_up || drift_down) {
level_ = Level::kVerified;
} else if ((probable_drift_up || probable_drift_down) &&
level_ == Level::kNone) {
level_ = Level::kProbable;
}
// Shift delay history one step.
delay_history_[2] = delay_history_[1];
delay_history_[1] = delay_history_[0];
delay_history_[0] = delay_estimate;
}
} // namespace webrtc
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