Moved and simplifed the AEC3 API call skew estimator and added tests

This CL moves the AEC3 API call skew estimator into a separate file.
This has the advantage that it can more easily be tested.
The CL also simplifies the code and adds unittests.

Bug: webrtc:8671
Change-Id: I19bc31ca5666cdc87a1ed14770ef20ead1b5b80d
Reviewed-on: https://webrtc-review.googlesource.com/55860
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22144}

modules/audio_processing/BUILD.gn

@@ -101,6 +101,8 @@ rtc_static_library("audio_processing") {
     "aec3/residual_echo_estimator.h",
     "aec3/shadow_filter_update_gain.cc",
     "aec3/shadow_filter_update_gain.h",
+    "aec3/skew_estimator.cc",
+    "aec3/skew_estimator.h",
     "aec3/subtractor.cc",
     "aec3/subtractor.h",
     "aec3/subtractor_output.h",
@@ -665,6 +667,7 @@ if (rtc_include_tests) {
         "aec3/render_signal_analyzer_unittest.cc",
         "aec3/residual_echo_estimator_unittest.cc",
         "aec3/shadow_filter_update_gain_unittest.cc",
+        "aec3/skew_estimator_unittest.cc",
         "aec3/subtractor_unittest.cc",
         "aec3/suppression_filter_unittest.cc",
         "aec3/suppression_gain_unittest.cc",

modules/audio_processing/aec3/render_delay_controller.cc

@@ -19,6 +19,7 @@
 #include "modules/audio_processing/aec3/aec3_common.h"
 #include "modules/audio_processing/aec3/echo_path_delay_estimator.h"
 #include "modules/audio_processing/aec3/render_delay_controller_metrics.h"
+#include "modules/audio_processing/aec3/skew_estimator.h"
 #include "rtc_base/atomicops.h"
 #include "rtc_base/constructormagic.h"
 
@@ -28,45 +29,6 @@ namespace {
 
 constexpr int kSkewHistorySizeLog2 = 8;
 
-// Estimator of API call skew between render and capture.
-class SkewEstimator {
- public:
-  // Resets the estimation.
-  void Reset() {
-    skew_ = 0;
-    next_index_ = 0;
-    sufficient_skew_stored_ = false;
-  }
-
-  // Updates the skew data for a render call.
-  void LogRenderCall() { ++skew_; }
-
-  // Updates and computes the skew at a capture call. Returns an optional which
-  // is non-null if a reliable skew has been found.
-  rtc::Optional<int> GetSkewFromCapture() {
-    --skew_;
-
-    skew_history_[next_index_] = skew_;
-    if (++next_index_ == skew_history_.size()) {
-      next_index_ = 0;
-      sufficient_skew_stored_ = true;
-    }
-
-    if (!sufficient_skew_stored_) {
-      return rtc::nullopt;
-    }
-
-    return std::accumulate(skew_history_.begin(), skew_history_.end(), 0) >>
-           kSkewHistorySizeLog2;
-  }
-
- private:
-  int skew_ = 0;
-  std::array<int, 1 << kSkewHistorySizeLog2> skew_history_;
-  size_t next_index_ = 0;
-  bool sufficient_skew_stored_ = false;
-};
-
 class RenderDelayControllerImpl final : public RenderDelayController {
  public:
   RenderDelayControllerImpl(const EchoCanceller3Config& config,
@@ -150,7 +112,8 @@ RenderDelayControllerImpl::RenderDelayControllerImpl(
       hysteresis_limit_2_blocks_(
           static_cast<int>(config.delay.hysteresis_limit_2_blocks)),
       delay_estimator_(data_dumper_.get(), config),
-      delay_buf_(kBlockSize * non_causal_offset, 0.f) {
+      delay_buf_(kBlockSize * non_causal_offset, 0.f),
+      skew_estimator_(kSkewHistorySizeLog2) {
   RTC_DCHECK(ValidFullBandRate(sample_rate_hz));
   delay_estimator_.LogDelayEstimationProperties(sample_rate_hz,
                                                 delay_buf_.size());

modules/audio_processing/aec3/skew_estimator.cc

@@ -0,0 +1,46 @@
+/*
+ *  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/skew_estimator.h"
+
+#include <algorithm>
+#include <numeric>
+
+namespace webrtc {
+
+SkewEstimator::SkewEstimator(size_t skew_history_size_log2)
+    : skew_history_size_log2_(static_cast<int>(skew_history_size_log2)),
+      skew_history_(1ULL << skew_history_size_log2_, 0) {}
+
+SkewEstimator::~SkewEstimator() = default;
+
+void SkewEstimator::Reset() {
+  skew_ = 0;
+  skew_sum_ = 0;
+  next_index_ = 0;
+  sufficient_skew_stored_ = false;
+  std::fill(skew_history_.begin(), skew_history_.end(), 0);
+}
+
+rtc::Optional<int> SkewEstimator::GetSkewFromCapture() {
+  --skew_;
+
+  skew_sum_ += skew_ - skew_history_[next_index_];
+  skew_history_[next_index_] = skew_;
+  if (++next_index_ == skew_history_.size()) {
+    next_index_ = 0;
+    sufficient_skew_stored_ = true;
+  }
+
+  return sufficient_skew_stored_
+             ? rtc::Optional<int>(skew_sum_ >> skew_history_size_log2_)
+             : rtc::nullopt;
+}
+
+}  // namespace webrtc

modules/audio_processing/aec3/skew_estimator.h

@@ -0,0 +1,50 @@
+/*
+ *  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.
+ */
+
+#ifndef MODULES_AUDIO_PROCESSING_AEC3_SKEW_ESTIMATOR_H_
+#define MODULES_AUDIO_PROCESSING_AEC3_SKEW_ESTIMATOR_H_
+
+#include <vector>
+
+#include "api/optional.h"
+#include "rtc_base/constructormagic.h"
+
+namespace webrtc {
+
+// Estimator of API call skew between render and capture.
+class SkewEstimator {
+ public:
+  explicit SkewEstimator(size_t skew_history_size_log2);
+  ~SkewEstimator();
+
+  // Resets the estimation.
+  void Reset();
+
+  // Updates the skew data for a render call.
+  void LogRenderCall() { ++skew_; }
+
+  // Updates and computes the skew at a capture call. Returns an optional which
+  // is non-null if a reliable skew has been found.
+  rtc::Optional<int> GetSkewFromCapture();
+
+ private:
+  const int skew_history_size_log2_;
+  std::vector<float> skew_history_;
+  int skew_ = 0;
+  int skew_sum_ = 0;
+  size_t next_index_ = 0;
+  bool sufficient_skew_stored_ = false;
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(SkewEstimator);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_AUDIO_PROCESSING_AEC3_SKEW_ESTIMATOR_H_

modules/audio_processing/aec3/skew_estimator_unittest.cc

@@ -0,0 +1,124 @@
+/*
+ *  Copyright (c) 2017 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/skew_estimator.h"
+
+#include "test/gtest.h"
+
+namespace webrtc {
+namespace aec3 {
+
+// Tests that the skew ends up as it should after a skew change.
+TEST(SkewEstimator, SkewChangeAdaptation) {
+  constexpr int kNumSkewsLog2 = 7;
+  constexpr int kNumSkews = 1 << kNumSkewsLog2;
+
+  SkewEstimator estimator(kNumSkewsLog2);
+
+  for (int k = 0; k < kNumSkews - 1; ++k) {
+    estimator.LogRenderCall();
+    auto skew = estimator.GetSkewFromCapture();
+    EXPECT_FALSE(skew);
+  }
+
+  estimator.LogRenderCall();
+
+  rtc::Optional<int> skew;
+  for (int k = 0; k < kNumSkews; ++k) {
+    estimator.LogRenderCall();
+    skew = estimator.GetSkewFromCapture();
+    EXPECT_TRUE(skew);
+  }
+  EXPECT_EQ(1, *skew);
+
+  estimator.LogRenderCall();
+
+  for (int k = 0; k < kNumSkews; ++k) {
+    estimator.LogRenderCall();
+    skew = estimator.GetSkewFromCapture();
+    EXPECT_TRUE(skew);
+  }
+  EXPECT_EQ(2, *skew);
+}
+
+// Tests that the skew ends up as it should for a surplus of render calls.
+TEST(SkewEstimator, SkewForSurplusRender) {
+  constexpr int kNumSkewsLog2 = 7;
+  constexpr int kNumSkews = 1 << kNumSkewsLog2;
+
+  SkewEstimator estimator(kNumSkewsLog2);
+
+  for (int k = 0; k < kNumSkews - 1; ++k) {
+    estimator.LogRenderCall();
+    auto skew = estimator.GetSkewFromCapture();
+    EXPECT_FALSE(skew);
+  }
+
+  estimator.LogRenderCall();
+
+  rtc::Optional<int> skew;
+  for (int k = 0; k < kNumSkews; ++k) {
+    estimator.LogRenderCall();
+    skew = estimator.GetSkewFromCapture();
+    EXPECT_TRUE(skew);
+  }
+  EXPECT_EQ(1, *skew);
+}
+
+// Tests that the skew ends up as it should for a surplus of capture calls.
+TEST(SkewEstimator, SkewForSurplusCapture) {
+  constexpr int kNumSkewsLog2 = 7;
+  constexpr int kNumSkews = 1 << kNumSkewsLog2;
+
+  SkewEstimator estimator(kNumSkewsLog2);
+
+  for (int k = 0; k < kNumSkews - 1; ++k) {
+    estimator.LogRenderCall();
+    auto skew = estimator.GetSkewFromCapture();
+    EXPECT_FALSE(skew);
+  }
+
+  rtc::Optional<int> skew;
+  skew = estimator.GetSkewFromCapture();
+
+  for (int k = 0; k < kNumSkews; ++k) {
+    estimator.LogRenderCall();
+    skew = estimator.GetSkewFromCapture();
+    EXPECT_TRUE(skew);
+  }
+  EXPECT_EQ(-1, *skew);
+}
+
+// Tests that the skew estimator returns a null optional when it should.
+TEST(SkewEstimator, NullEstimate) {
+  constexpr int kNumSkewsLog2 = 4;
+  constexpr int kNumSkews = 1 << kNumSkewsLog2;
+
+  SkewEstimator estimator(kNumSkewsLog2);
+
+  for (int k = 0; k < kNumSkews - 1; ++k) {
+    estimator.LogRenderCall();
+    auto skew = estimator.GetSkewFromCapture();
+    EXPECT_FALSE(skew);
+  }
+
+  estimator.LogRenderCall();
+  auto skew = estimator.GetSkewFromCapture();
+  EXPECT_TRUE(skew);
+
+  estimator.Reset();
+  for (int k = 0; k < kNumSkews - 1; ++k) {
+    estimator.LogRenderCall();
+    auto skew = estimator.GetSkewFromCapture();
+    EXPECT_FALSE(skew);
+  }
+}
+}  // namespace aec3
+}  // namespace webrtc