Refactor delay manager.

Split out `RelativeArrivalDelayTracker` and `DelayOptimizer` logic.

This is in preparation for adding another `DelayOptimizer` specialized in handling reordered packets.

Bug: webrtc:10178
Change-Id: Id3c1746d91980b171fa524f9b2b71cf11fc75f64
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/231224
Commit-Queue: Jakob Ivarsson <jakobi@webrtc.org>
Reviewed-by: Ivo Creusen <ivoc@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#34938}

modules/audio_coding/neteq/underrun_optimizer.cc

@@ -0,0 +1,71 @@
+/*
+ *  Copyright (c) 2021 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_coding/neteq/underrun_optimizer.h"
+
+#include <algorithm>
+
+namespace webrtc {
+
+namespace {
+
+constexpr int kDelayBuckets = 100;
+constexpr int kBucketSizeMs = 20;
+
+}  // namespace
+
+UnderrunOptimizer::UnderrunOptimizer(const TickTimer* tick_timer,
+                                     int histogram_quantile,
+                                     int forget_factor,
+                                     absl::optional<int> start_forget_weight,
+                                     absl::optional<int> resample_interval_ms)
+    : tick_timer_(tick_timer),
+      histogram_(kDelayBuckets, forget_factor, start_forget_weight),
+      histogram_quantile_(histogram_quantile),
+      resample_interval_ms_(resample_interval_ms) {}
+
+void UnderrunOptimizer::Update(int relative_delay_ms) {
+  absl::optional<int> histogram_update;
+  if (resample_interval_ms_) {
+    if (!resample_stopwatch_) {
+      resample_stopwatch_ = tick_timer_->GetNewStopwatch();
+    }
+    if (static_cast<int>(resample_stopwatch_->ElapsedMs()) >
+        *resample_interval_ms_) {
+      histogram_update = max_delay_in_interval_ms_;
+      resample_stopwatch_ = tick_timer_->GetNewStopwatch();
+      max_delay_in_interval_ms_ = 0;
+    }
+    max_delay_in_interval_ms_ =
+        std::max(max_delay_in_interval_ms_, relative_delay_ms);
+  } else {
+    histogram_update = relative_delay_ms;
+  }
+  if (!histogram_update) {
+    return;
+  }
+
+  const int index = *histogram_update / kBucketSizeMs;
+  if (index < histogram_.NumBuckets()) {
+    // Maximum delay to register is 2000 ms.
+    histogram_.Add(index);
+  }
+  int bucket_index = histogram_.Quantile(histogram_quantile_);
+  optimal_delay_ms_ = (1 + bucket_index) * kBucketSizeMs;
+}
+
+void UnderrunOptimizer::Reset() {
+  histogram_.Reset();
+  resample_stopwatch_ = tick_timer_->GetNewStopwatch();
+  max_delay_in_interval_ms_ = 0;
+  optimal_delay_ms_.reset();
+}
+
+}  // namespace webrtc