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diff --git a/dom/media/AudioSegment.h b/dom/media/AudioSegment.h
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+++ b/dom/media/AudioSegment.h
@@ -0,0 +1,482 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* 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 MOZILLA_AUDIOSEGMENT_H_
+#define MOZILLA_AUDIOSEGMENT_H_
+
+#include <speex/speex_resampler.h>
+#include "MediaSegment.h"
+#include "AudioSampleFormat.h"
+#include "AudioChannelFormat.h"
+#include "SharedBuffer.h"
+#include "WebAudioUtils.h"
+#include "mozilla/ScopeExit.h"
+#include "nsAutoRef.h"
+#ifdef MOZILLA_INTERNAL_API
+#  include "mozilla/TimeStamp.h"
+#endif
+#include <float.h>
+
+namespace mozilla {
+struct AudioChunk;
+class AudioSegment;
+}  // namespace mozilla
+MOZ_DECLARE_RELOCATE_USING_MOVE_CONSTRUCTOR(mozilla::AudioChunk)
+
+/**
+ * This allows compilation of nsTArray<AudioSegment> and
+ * AutoTArray<AudioSegment> since without it, static analysis fails on the
+ * mChunks member being a non-memmovable AutoTArray.
+ *
+ * Note that AudioSegment(const AudioSegment&) is deleted, so this should
+ * never come into effect.
+ */
+MOZ_DECLARE_RELOCATE_USING_MOVE_CONSTRUCTOR(mozilla::AudioSegment)
+
+namespace mozilla {
+
+template <typename T>
+class SharedChannelArrayBuffer : public ThreadSharedObject {
+ public:
+  explicit SharedChannelArrayBuffer(nsTArray<nsTArray<T> >&& aBuffers)
+      : mBuffers(std::move(aBuffers)) {}
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const override {
+    size_t amount = 0;
+    amount += mBuffers.ShallowSizeOfExcludingThis(aMallocSizeOf);
+    for (size_t i = 0; i < mBuffers.Length(); i++) {
+      amount += mBuffers[i].ShallowSizeOfExcludingThis(aMallocSizeOf);
+    }
+
+    return amount;
+  }
+
+  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const override {
+    return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  nsTArray<nsTArray<T> > mBuffers;
+};
+
+class AudioMixer;
+
+/**
+ * For auto-arrays etc, guess this as the common number of channels.
+ */
+const int GUESS_AUDIO_CHANNELS = 2;
+
+// We ensure that the graph advances in steps that are multiples of the Web
+// Audio block size
+const uint32_t WEBAUDIO_BLOCK_SIZE_BITS = 7;
+const uint32_t WEBAUDIO_BLOCK_SIZE = 1 << WEBAUDIO_BLOCK_SIZE_BITS;
+
+template <typename SrcT, typename DestT>
+static void InterleaveAndConvertBuffer(const SrcT* const* aSourceChannels,
+                                       uint32_t aLength, float aVolume,
+                                       uint32_t aChannels, DestT* aOutput) {
+  DestT* output = aOutput;
+  for (size_t i = 0; i < aLength; ++i) {
+    for (size_t channel = 0; channel < aChannels; ++channel) {
+      float v = AudioSampleToFloat(aSourceChannels[channel][i]) * aVolume;
+      *output = FloatToAudioSample<DestT>(v);
+      ++output;
+    }
+  }
+}
+
+template <typename SrcT, typename DestT>
+static void DeinterleaveAndConvertBuffer(const SrcT* aSourceBuffer,
+                                         uint32_t aFrames, uint32_t aChannels,
+                                         DestT** aOutput) {
+  for (size_t i = 0; i < aChannels; i++) {
+    size_t interleavedIndex = i;
+    for (size_t j = 0; j < aFrames; j++) {
+      ConvertAudioSample(aSourceBuffer[interleavedIndex], aOutput[i][j]);
+      interleavedIndex += aChannels;
+    }
+  }
+}
+
+class SilentChannel {
+ public:
+  static const int AUDIO_PROCESSING_FRAMES = 640; /* > 10ms of 48KHz audio */
+  static const uint8_t
+      gZeroChannel[MAX_AUDIO_SAMPLE_SIZE * AUDIO_PROCESSING_FRAMES];
+  // We take advantage of the fact that zero in float and zero in int have the
+  // same all-zeros bit layout.
+  template <typename T>
+  static const T* ZeroChannel();
+};
+
+/**
+ * Given an array of input channels (aChannelData), downmix to aOutputChannels,
+ * interleave the channel data. A total of aOutputChannels*aDuration
+ * interleaved samples will be copied to a channel buffer in aOutput.
+ */
+template <typename SrcT, typename DestT>
+void DownmixAndInterleave(Span<const SrcT* const> aChannelData,
+                          int32_t aDuration, float aVolume,
+                          uint32_t aOutputChannels, DestT* aOutput) {
+  if (aChannelData.Length() == aOutputChannels) {
+    InterleaveAndConvertBuffer(aChannelData.Elements(), aDuration, aVolume,
+                               aOutputChannels, aOutput);
+  } else {
+    AutoTArray<SrcT*, GUESS_AUDIO_CHANNELS> outputChannelData;
+    AutoTArray<SrcT,
+               SilentChannel::AUDIO_PROCESSING_FRAMES * GUESS_AUDIO_CHANNELS>
+        outputBuffers;
+    outputChannelData.SetLength(aOutputChannels);
+    outputBuffers.SetLength(aDuration * aOutputChannels);
+    for (uint32_t i = 0; i < aOutputChannels; i++) {
+      outputChannelData[i] = outputBuffers.Elements() + aDuration * i;
+    }
+    AudioChannelsDownMix<SrcT, SrcT>(aChannelData, outputChannelData,
+                                     aDuration);
+    InterleaveAndConvertBuffer(outputChannelData.Elements(), aDuration, aVolume,
+                               aOutputChannels, aOutput);
+  }
+}
+
+/**
+ * An AudioChunk represents a multi-channel buffer of audio samples.
+ * It references an underlying ThreadSharedObject which manages the lifetime
+ * of the buffer. An AudioChunk maintains its own duration and channel data
+ * pointers so it can represent a subinterval of a buffer without copying.
+ * An AudioChunk can store its individual channels anywhere; it maintains
+ * separate pointers to each channel's buffer.
+ */
+struct AudioChunk {
+  typedef mozilla::AudioSampleFormat SampleFormat;
+
+  AudioChunk() = default;
+
+  template <typename T>
+  AudioChunk(already_AddRefed<ThreadSharedObject> aBuffer,
+             const nsTArray<const T*>& aChannelData, TrackTime aDuration,
+             PrincipalHandle aPrincipalHandle)
+      : mDuration(aDuration),
+        mBuffer(aBuffer),
+        mBufferFormat(AudioSampleTypeToFormat<T>::Format),
+        mPrincipalHandle(std::move(aPrincipalHandle)) {
+    MOZ_ASSERT(!mBuffer == aChannelData.IsEmpty(), "Appending invalid data ?");
+    for (const T* data : aChannelData) {
+      mChannelData.AppendElement(data);
+    }
+  }
+
+  // Generic methods
+  void SliceTo(TrackTime aStart, TrackTime aEnd) {
+    MOZ_ASSERT(aStart >= 0, "Slice out of bounds: invalid start");
+    MOZ_ASSERT(aStart < aEnd, "Slice out of bounds: invalid range");
+    MOZ_ASSERT(aEnd <= mDuration, "Slice out of bounds: invalid end");
+
+    if (mBuffer) {
+      MOZ_ASSERT(aStart < INT32_MAX,
+                 "Can't slice beyond 32-bit sample lengths");
+      for (uint32_t channel = 0; channel < mChannelData.Length(); ++channel) {
+        mChannelData[channel] = AddAudioSampleOffset(
+            mChannelData[channel], mBufferFormat, int32_t(aStart));
+      }
+    }
+    mDuration = aEnd - aStart;
+  }
+  TrackTime GetDuration() const { return mDuration; }
+  bool CanCombineWithFollowing(const AudioChunk& aOther) const {
+    if (aOther.mBuffer != mBuffer) {
+      return false;
+    }
+    if (!mBuffer) {
+      return true;
+    }
+    if (aOther.mVolume != mVolume) {
+      return false;
+    }
+    if (aOther.mPrincipalHandle != mPrincipalHandle) {
+      return false;
+    }
+    NS_ASSERTION(aOther.mBufferFormat == mBufferFormat,
+                 "Wrong metadata about buffer");
+    NS_ASSERTION(aOther.mChannelData.Length() == mChannelData.Length(),
+                 "Mismatched channel count");
+    if (mDuration > INT32_MAX) {
+      return false;
+    }
+    for (uint32_t channel = 0; channel < mChannelData.Length(); ++channel) {
+      if (aOther.mChannelData[channel] !=
+          AddAudioSampleOffset(mChannelData[channel], mBufferFormat,
+                               int32_t(mDuration))) {
+        return false;
+      }
+    }
+    return true;
+  }
+  bool IsNull() const { return mBuffer == nullptr; }
+  void SetNull(TrackTime aDuration) {
+    mBuffer = nullptr;
+    mChannelData.Clear();
+    mDuration = aDuration;
+    mVolume = 1.0f;
+    mBufferFormat = AUDIO_FORMAT_SILENCE;
+    mPrincipalHandle = PRINCIPAL_HANDLE_NONE;
+  }
+
+  uint32_t ChannelCount() const { return mChannelData.Length(); }
+
+  bool IsMuted() const { return mVolume == 0.0f; }
+
+  size_t SizeOfExcludingThisIfUnshared(MallocSizeOf aMallocSizeOf) const {
+    return SizeOfExcludingThis(aMallocSizeOf, true);
+  }
+
+  size_t SizeOfExcludingThis(MallocSizeOf aMallocSizeOf, bool aUnshared) const {
+    size_t amount = 0;
+
+    // Possibly owned:
+    // - mBuffer - Can hold data that is also in the decoded audio queue. If it
+    //             is not shared, or unshared == false it gets counted.
+    if (mBuffer && (!aUnshared || !mBuffer->IsShared())) {
+      amount += mBuffer->SizeOfIncludingThis(aMallocSizeOf);
+    }
+
+    // Memory in the array is owned by mBuffer.
+    amount += mChannelData.ShallowSizeOfExcludingThis(aMallocSizeOf);
+    return amount;
+  }
+
+  template <typename T>
+  Span<const T* const> ChannelData() const {
+    MOZ_ASSERT(AudioSampleTypeToFormat<T>::Format == mBufferFormat);
+    return Span(reinterpret_cast<const T* const*>(mChannelData.Elements()),
+                mChannelData.Length());
+  }
+
+  /**
+   * ChannelFloatsForWrite() should be used only when mBuffer is owned solely
+   * by the calling thread.
+   */
+  template <typename T>
+  T* ChannelDataForWrite(size_t aChannel) {
+    MOZ_ASSERT(AudioSampleTypeToFormat<T>::Format == mBufferFormat);
+    MOZ_ASSERT(!mBuffer->IsShared());
+    return static_cast<T*>(const_cast<void*>(mChannelData[aChannel]));
+  }
+
+  template <typename T>
+  static AudioChunk FromInterleavedBuffer(
+      const T* aBuffer, size_t aFrames, uint32_t aChannels,
+      const PrincipalHandle& aPrincipalHandle) {
+    CheckedInt<size_t> bufferSize(sizeof(T));
+    bufferSize *= aFrames;
+    bufferSize *= aChannels;
+    RefPtr<SharedBuffer> buffer = SharedBuffer::Create(bufferSize);
+
+    AutoTArray<T*, 8> deinterleaved;
+    if (aChannels == 1) {
+      PodCopy(static_cast<T*>(buffer->Data()), aBuffer, aFrames);
+      deinterleaved.AppendElement(static_cast<T*>(buffer->Data()));
+    } else {
+      deinterleaved.SetLength(aChannels);
+      T* samples = static_cast<T*>(buffer->Data());
+
+      size_t offset = 0;
+      for (uint32_t i = 0; i < aChannels; ++i) {
+        deinterleaved[i] = samples + offset;
+        offset += aFrames;
+      }
+
+      DeinterleaveAndConvertBuffer(aBuffer, static_cast<uint32_t>(aFrames),
+                                   aChannels, deinterleaved.Elements());
+    }
+
+    AutoTArray<const T*, GUESS_AUDIO_CHANNELS> channelData;
+    channelData.AppendElements(deinterleaved);
+    return AudioChunk(buffer.forget(), channelData,
+                      static_cast<TrackTime>(aFrames), aPrincipalHandle);
+  }
+
+  const PrincipalHandle& GetPrincipalHandle() const { return mPrincipalHandle; }
+
+  // aOutputChannels must contain pointers to channel data of length mDuration.
+  void DownMixTo(Span<AudioDataValue* const> aOutputChannels) const;
+
+  TrackTime mDuration = 0;             // in frames within the buffer
+  RefPtr<ThreadSharedObject> mBuffer;  // the buffer object whose lifetime is
+                                       // managed; null means data is all zeroes
+  // one pointer per channel; empty if and only if mBuffer is null
+  CopyableAutoTArray<const void*, GUESS_AUDIO_CHANNELS> mChannelData;
+  float mVolume = 1.0f;  // volume multiplier to apply
+  // format of frames in mBuffer (or silence if mBuffer is null)
+  SampleFormat mBufferFormat = AUDIO_FORMAT_SILENCE;
+  // principalHandle for the data in this chunk.
+  // This can be compared to an nsIPrincipal* when back on main thread.
+  PrincipalHandle mPrincipalHandle = PRINCIPAL_HANDLE_NONE;
+};
+
+/**
+ * A list of audio samples consisting of a sequence of slices of SharedBuffers.
+ * The audio rate is determined by the track, not stored in this class.
+ */
+class AudioSegment : public MediaSegmentBase<AudioSegment, AudioChunk> {
+  // The channel count that MaxChannelCount() returned last time it was called.
+  uint32_t mMemoizedMaxChannelCount = 0;
+
+ public:
+  typedef mozilla::AudioSampleFormat SampleFormat;
+
+  AudioSegment() : MediaSegmentBase<AudioSegment, AudioChunk>(AUDIO) {}
+
+  AudioSegment(AudioSegment&& aSegment) = default;
+
+  AudioSegment(const AudioSegment&) = delete;
+  AudioSegment& operator=(const AudioSegment&) = delete;
+
+  ~AudioSegment() = default;
+
+  // Resample the whole segment in place.  `aResampler` is an instance of a
+  // resampler, initialized with `aResamplerChannelCount` channels. If this
+  // function finds a chunk with more channels, `aResampler` is destroyed and a
+  // new resampler is created, and `aResamplerChannelCount` is updated with the
+  // new channel count value.
+  void ResampleChunks(nsAutoRef<SpeexResamplerState>& aResampler,
+                      uint32_t* aResamplerChannelCount, uint32_t aInRate,
+                      uint32_t aOutRate);
+
+  template <typename T>
+  void AppendFrames(already_AddRefed<ThreadSharedObject> aBuffer,
+                    const nsTArray<const T*>& aChannelData, TrackTime aDuration,
+                    const PrincipalHandle& aPrincipalHandle) {
+    AppendAndConsumeChunk(AudioChunk(std::move(aBuffer), aChannelData,
+                                     aDuration, aPrincipalHandle));
+  }
+  void AppendSegment(const AudioSegment* aSegment) {
+    MOZ_ASSERT(aSegment);
+
+    for (const AudioChunk& c : aSegment->mChunks) {
+      AudioChunk* chunk = AppendChunk(c.GetDuration());
+      chunk->mBuffer = c.mBuffer;
+      chunk->mChannelData = c.mChannelData;
+      chunk->mBufferFormat = c.mBufferFormat;
+      chunk->mPrincipalHandle = c.mPrincipalHandle;
+    }
+  }
+  template <typename T>
+  void AppendFromInterleavedBuffer(const T* aBuffer, size_t aFrames,
+                                   uint32_t aChannels,
+                                   const PrincipalHandle& aPrincipalHandle) {
+    AppendAndConsumeChunk(AudioChunk::FromInterleavedBuffer<T>(
+        aBuffer, aFrames, aChannels, aPrincipalHandle));
+  }
+  // Write the segement data into an interleaved buffer. Do mixing if the
+  // AudioChunk's channel count in the segment is different from aChannels.
+  // Returns sample count of the converted audio data. The converted data will
+  // be stored into aBuffer.
+  size_t WriteToInterleavedBuffer(nsTArray<AudioDataValue>& aBuffer,
+                                  uint32_t aChannels) const;
+  // Consumes aChunk, and append it to the segment if its duration is not zero.
+  void AppendAndConsumeChunk(AudioChunk&& aChunk) {
+    AudioChunk unused;
+    AudioChunk* chunk = &unused;
+
+    // Always consume aChunk. The chunk's mBuffer can be non-null even if its
+    // duration is 0.
+    auto consume = MakeScopeExit([&] {
+      chunk->mBuffer = std::move(aChunk.mBuffer);
+      chunk->mChannelData = std::move(aChunk.mChannelData);
+
+      MOZ_ASSERT(chunk->mBuffer || chunk->mChannelData.IsEmpty(),
+                 "Appending invalid data ?");
+
+      chunk->mVolume = aChunk.mVolume;
+      chunk->mBufferFormat = aChunk.mBufferFormat;
+      chunk->mPrincipalHandle = std::move(aChunk.mPrincipalHandle);
+    });
+
+    if (aChunk.GetDuration() == 0) {
+      return;
+    }
+
+    if (!mChunks.IsEmpty() &&
+        mChunks.LastElement().CanCombineWithFollowing(aChunk)) {
+      mChunks.LastElement().mDuration += aChunk.GetDuration();
+      mDuration += aChunk.GetDuration();
+      return;
+    }
+
+    chunk = AppendChunk(aChunk.mDuration);
+  }
+  void ApplyVolume(float aVolume);
+  // Mix the segment into a mixer, keeping it planar, up or down mixing to
+  // aChannelCount channels.
+  void Mix(AudioMixer& aMixer, uint32_t aChannelCount, uint32_t aSampleRate);
+
+  // Returns the maximum channel count across all chunks in this segment.
+  // Should there be no chunk with a channel count we return the memoized return
+  // value from last time this method was called.
+  uint32_t MaxChannelCount() {
+    uint32_t channelCount = 0;
+    for (ChunkIterator ci(*this); !ci.IsEnded(); ci.Next()) {
+      if (ci->ChannelCount()) {
+        channelCount = std::max(channelCount, ci->ChannelCount());
+      }
+    }
+    if (channelCount == 0) {
+      return mMemoizedMaxChannelCount;
+    }
+    return mMemoizedMaxChannelCount = channelCount;
+  }
+
+  static Type StaticType() { return AUDIO; }
+
+  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const override {
+    return aMallocSizeOf(this) + SizeOfExcludingThis(aMallocSizeOf);
+  }
+
+  PrincipalHandle GetOldestPrinciple() const {
+    const AudioChunk* chunk = mChunks.IsEmpty() ? nullptr : &mChunks[0];
+    return chunk ? chunk->GetPrincipalHandle() : PRINCIPAL_HANDLE_NONE;
+  }
+
+  // Iterate on each chunks until the input function returns true.
+  template <typename Function>
+  void IterateOnChunks(const Function&& aFunction) {
+    for (uint32_t idx = 0; idx < mChunks.Length(); idx++) {
+      if (aFunction(&mChunks[idx])) {
+        return;
+      }
+    }
+  }
+
+ private:
+  template <typename T>
+  void Resample(nsAutoRef<SpeexResamplerState>& aResampler,
+                uint32_t* aResamplerChannelCount, uint32_t aInRate,
+                uint32_t aOutRate);
+};
+
+template <typename SrcT>
+void WriteChunk(const AudioChunk& aChunk, uint32_t aOutputChannels,
+                float aVolume, AudioDataValue* aOutputBuffer) {
+  CopyableAutoTArray<const SrcT*, GUESS_AUDIO_CHANNELS> channelData;
+  channelData.AppendElements(aChunk.ChannelData<SrcT>());
+
+  if (channelData.Length() < aOutputChannels) {
+    // Up-mix. Note that this might actually make channelData have more
+    // than aOutputChannels temporarily.
+    AudioChannelsUpMix(&channelData, aOutputChannels,
+                       SilentChannel::ZeroChannel<SrcT>());
+  }
+  if (channelData.Length() > aOutputChannels) {
+    // Down-mix.
+    DownmixAndInterleave<SrcT>(channelData, aChunk.mDuration, aVolume,
+                               aOutputChannels, aOutputBuffer);
+  } else {
+    InterleaveAndConvertBuffer(channelData.Elements(), aChunk.mDuration,
+                               aVolume, aOutputChannels, aOutputBuffer);
+  }
+}
+
+}  // namespace mozilla
+
+#endif /* MOZILLA_AUDIOSEGMENT_H_ */