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diff --git a/dom/media/webaudio/DelayBuffer.h b/dom/media/webaudio/DelayBuffer.h
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+++ b/dom/media/webaudio/DelayBuffer.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DelayBuffer_h_
+#define DelayBuffer_h_
+
+#include "nsTArray.h"
+#include "AudioSegment.h"
+#include "mozilla/dom/AudioNodeBinding.h" // for ChannelInterpretation
+
+namespace mozilla {
+
+class DelayBuffer final
+{
+  typedef dom::ChannelInterpretation ChannelInterpretation;
+
+public:
+  // See WebAudioUtils::ComputeSmoothingRate() for frame to frame exponential
+  // |smoothingRate| multiplier.
+  DelayBuffer(double aMaxDelayTicks, double aSmoothingRate)
+    : mSmoothingRate(aSmoothingRate)
+    , mCurrentDelay(-1.0)
+    // Round the maximum delay up to the next tick.
+    , mMaxDelayTicks(ceil(aMaxDelayTicks))
+    , mCurrentChunk(0)
+    // mLastReadChunk is initialized in EnsureBuffer
+#ifdef DEBUG
+    , mHaveWrittenBlock(false)
+#endif
+  {
+    // The 180 second limit in AudioContext::CreateDelay() and the
+    // 1 << MEDIA_TIME_FRAC_BITS limit on sample rate provide a limit on the
+    // maximum delay.
+    MOZ_ASSERT(aMaxDelayTicks <=
+               std::numeric_limits<decltype(mMaxDelayTicks)>::max());
+  }
+
+  // Write a WEBAUDIO_BLOCK_SIZE block for aChannelCount channels.
+  void Write(const AudioBlock& aInputChunk);
+
+  // Read a block with an array of delays, in ticks, for each sample frame.
+  // Each delay should be >= 0 and <= MaxDelayTicks().
+  void Read(const double aPerFrameDelays[WEBAUDIO_BLOCK_SIZE],
+            AudioBlock* aOutputChunk,
+            ChannelInterpretation aChannelInterpretation);
+  // Read a block with a constant delay, which will be smoothed with the
+  // previous delay.  The delay should be >= 0 and <= MaxDelayTicks().
+  void Read(double aDelayTicks, AudioBlock* aOutputChunk,
+            ChannelInterpretation aChannelInterpretation);
+
+  // Read into one of the channels of aOutputChunk, given an array of
+  // delays in ticks.  This is useful when delays are different on different
+  // channels.  aOutputChunk must have already been allocated with at least as
+  // many channels as were in any of the blocks passed to Write().
+  void ReadChannel(const double aPerFrameDelays[WEBAUDIO_BLOCK_SIZE],
+                   AudioBlock* aOutputChunk, uint32_t aChannel,
+                   ChannelInterpretation aChannelInterpretation);
+
+  // Advance the buffer pointer
+  void NextBlock()
+  {
+    mCurrentChunk = (mCurrentChunk + 1) % mChunks.Length();
+#ifdef DEBUG
+    MOZ_ASSERT(mHaveWrittenBlock);
+    mHaveWrittenBlock = false;
+#endif
+  }
+
+  void Reset() {
+    mChunks.Clear();
+    mCurrentDelay = -1.0;
+  };
+
+  int MaxDelayTicks() const { return mMaxDelayTicks; }
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const;
+
+private:
+  void ReadChannels(const double aPerFrameDelays[WEBAUDIO_BLOCK_SIZE],
+                    AudioBlock* aOutputChunk,
+                    uint32_t aFirstChannel, uint32_t aNumChannelsToRead,
+                    ChannelInterpretation aChannelInterpretation);
+  bool EnsureBuffer();
+  int PositionForDelay(int aDelay);
+  int ChunkForPosition(int aPosition);
+  int OffsetForPosition(int aPosition);
+  int ChunkForDelay(int aDelay);
+  void UpdateUpmixChannels(int aNewReadChunk, uint32_t channelCount,
+                           ChannelInterpretation aChannelInterpretation);
+
+  // Circular buffer for capturing delayed samples.
+  FallibleTArray<AudioChunk> mChunks;
+  // Cache upmixed channel arrays.
+  AutoTArray<const float*,GUESS_AUDIO_CHANNELS> mUpmixChannels;
+  double mSmoothingRate;
+  // Current delay, in fractional ticks
+  double mCurrentDelay;
+  // Maximum delay, in ticks
+  int mMaxDelayTicks;
+  // The current position in the circular buffer.  The next write will be to
+  // this chunk, and the next read may begin before this chunk.
+  int mCurrentChunk;
+  // The chunk owning the pointers in mUpmixChannels
+  int mLastReadChunk;
+#ifdef DEBUG
+  bool mHaveWrittenBlock;
+#endif
+};
+
+} // namespace mozilla
+
+#endif // DelayBuffer_h_