1 /*
2 * Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10 #include "modules/audio_processing/aec3/clockdrift_detector.h"
11
12 namespace webrtc {
13
ClockdriftDetector()14 ClockdriftDetector::ClockdriftDetector()
15 : level_(Level::kNone), stability_counter_(0) {
16 delay_history_.fill(0);
17 }
18
19 ClockdriftDetector::~ClockdriftDetector() = default;
20
Update(int delay_estimate)21 void ClockdriftDetector::Update(int delay_estimate) {
22 if (delay_estimate == delay_history_[0]) {
23 // Reset clockdrift level if delay estimate is stable for 7500 blocks (30
24 // seconds).
25 if (++stability_counter_ > 7500)
26 level_ = Level::kNone;
27 return;
28 }
29
30 stability_counter_ = 0;
31 const int d1 = delay_history_[0] - delay_estimate;
32 const int d2 = delay_history_[1] - delay_estimate;
33 const int d3 = delay_history_[2] - delay_estimate;
34
35 // Patterns recognized as positive clockdrift:
36 // [x-3], x-2, x-1, x.
37 // [x-3], x-1, x-2, x.
38 const bool probable_drift_up =
39 (d1 == -1 && d2 == -2) || (d1 == -2 && d2 == -1);
40 const bool drift_up = probable_drift_up && d3 == -3;
41
42 // Patterns recognized as negative clockdrift:
43 // [x+3], x+2, x+1, x.
44 // [x+3], x+1, x+2, x.
45 const bool probable_drift_down = (d1 == 1 && d2 == 2) || (d1 == 2 && d2 == 1);
46 const bool drift_down = probable_drift_down && d3 == 3;
47
48 // Set clockdrift level.
49 if (drift_up || drift_down) {
50 level_ = Level::kVerified;
51 } else if ((probable_drift_up || probable_drift_down) &&
52 level_ == Level::kNone) {
53 level_ = Level::kProbable;
54 }
55
56 // Shift delay history one step.
57 delay_history_[2] = delay_history_[1];
58 delay_history_[1] = delay_history_[0];
59 delay_history_[0] = delay_estimate;
60 }
61 } // namespace webrtc
62