1 files changed, 81 insertions, 0 deletions
diff --git a/third_party/libwebrtc/sdk/android/src/java/org/webrtc/audio/LowLatencyAudioBufferManager.java b/third_party/libwebrtc/sdk/android/src/java/org/webrtc/audio/LowLatencyAudioBufferManager.java
new file mode 100644
index 0000000000..70c625ab4f
--- /dev/null
+++ b/third_party/libwebrtc/sdk/android/src/java/org/webrtc/audio/LowLatencyAudioBufferManager.java
@@ -0,0 +1,81 @@
+/*
+ *  Copyright (c) 2020 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.
+ */
+
+package org.webrtc.audio;
+
+import android.media.AudioTrack;
+import android.os.Build;
+import org.webrtc.Logging;
+
+// Lowers the buffer size if no underruns are detected for 100 ms. Once an
+// underrun is detected, the buffer size is increased by 10 ms and it will not
+// be lowered further. The buffer size will never be increased more than
+// 5 times, to avoid the possibility of the buffer size increasing without
+// bounds.
+class LowLatencyAudioBufferManager {
+  private static final String TAG = "LowLatencyAudioBufferManager";
+  // The underrun count that was valid during the previous call to maybeAdjustBufferSize(). Used to
+  // detect increases in the value.
+  private int prevUnderrunCount;
+  // The number of ticks to wait without an underrun before decreasing the buffer size.
+  private int ticksUntilNextDecrease;
+  // Indicate if we should continue to decrease the buffer size.
+  private boolean keepLoweringBufferSize;
+  // How often the buffer size was increased.
+  private int bufferIncreaseCounter;
+
+  public LowLatencyAudioBufferManager() {
+    this.prevUnderrunCount = 0;
+    this.ticksUntilNextDecrease = 10;
+    this.keepLoweringBufferSize = true;
+    this.bufferIncreaseCounter = 0;
+  }
+
+  public void maybeAdjustBufferSize(AudioTrack audioTrack) {
+    if (Build.VERSION.SDK_INT >= 26) {
+      final int underrunCount = audioTrack.getUnderrunCount();
+      if (underrunCount > prevUnderrunCount) {
+        // Don't increase buffer more than 5 times. Continuing to increase the buffer size
+        // could be harmful on low-power devices that regularly experience underruns under
+        // normal conditions.
+        if (bufferIncreaseCounter < 5) {
+          // Underrun detected, increase buffer size by 10ms.
+          final int currentBufferSize = audioTrack.getBufferSizeInFrames();
+          final int newBufferSize = currentBufferSize + audioTrack.getPlaybackRate() / 100;
+          Logging.d(TAG,
+              "Underrun detected! Increasing AudioTrack buffer size from " + currentBufferSize
+                  + " to " + newBufferSize);
+          audioTrack.setBufferSizeInFrames(newBufferSize);
+          bufferIncreaseCounter++;
+        }
+        // Stop trying to lower the buffer size.
+        keepLoweringBufferSize = false;
+        prevUnderrunCount = underrunCount;
+        ticksUntilNextDecrease = 10;
+      } else if (keepLoweringBufferSize) {
+        ticksUntilNextDecrease--;
+        if (ticksUntilNextDecrease <= 0) {
+          // No underrun seen for 100 ms, try to lower the buffer size by 10ms.
+          final int bufferSize10ms = audioTrack.getPlaybackRate() / 100;
+          // Never go below a buffer size of 10ms.
+          final int currentBufferSize = audioTrack.getBufferSizeInFrames();
+          final int newBufferSize = Math.max(bufferSize10ms, currentBufferSize - bufferSize10ms);
+          if (newBufferSize != currentBufferSize) {
+            Logging.d(TAG,
+                "Lowering AudioTrack buffer size from " + currentBufferSize + " to "
+                    + newBufferSize);
+            audioTrack.setBufferSizeInFrames(newBufferSize);
+          }
+          ticksUntilNextDecrease = 10;
+        }
+      }
+    }
+  }
+}