1 files changed, 208 insertions, 0 deletions
diff --git a/dom/media/AudioBufferUtils.h b/dom/media/AudioBufferUtils.h
new file mode 100644
index 0000000000..bb50fe3728
--- /dev/null
+++ b/dom/media/AudioBufferUtils.h
@@ -0,0 +1,208 @@
+/* -*- 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_SCRATCHBUFFER_H_
+#define MOZILLA_SCRATCHBUFFER_H_
+
+#include "mozilla/PodOperations.h"
+#include "mozilla/UniquePtr.h"
+#include "nsDebug.h"
+
+#include <algorithm>
+
+namespace mozilla {
+
+/**
+ * The classes in this file provide a interface that uses frames as a unit.
+ * However, they store their offsets in samples (because it's handy for pointer
+ * operations). Those functions can convert between the two units.
+ */
+static inline uint32_t FramesToSamples(uint32_t aChannels, uint32_t aFrames) {
+  return aFrames * aChannels;
+}
+
+static inline uint32_t SamplesToFrames(uint32_t aChannels, uint32_t aSamples) {
+  MOZ_ASSERT(!(aSamples % aChannels), "Frame alignment is wrong.");
+  return aSamples / aChannels;
+}
+
+/**
+ * Class that gets a buffer pointer from an audio callback and provides a safe
+ * interface to manipulate this buffer, and to ensure we are not missing frames
+ * by the end of the callback.
+ */
+template <typename T>
+class AudioCallbackBufferWrapper {
+ public:
+  AudioCallbackBufferWrapper()
+      : mBuffer(nullptr), mSamples(0), mSampleWriteOffset(1), mChannels(0) {}
+
+  explicit AudioCallbackBufferWrapper(uint32_t aChannels)
+      : mBuffer(nullptr),
+        mSamples(0),
+        mSampleWriteOffset(1),
+        mChannels(aChannels)
+
+  {
+    MOZ_ASSERT(aChannels);
+  }
+
+  AudioCallbackBufferWrapper& operator=(
+      const AudioCallbackBufferWrapper& aOther) {
+    MOZ_ASSERT(!aOther.mBuffer,
+               "Don't use this ctor after AudioCallbackDriver::Init");
+    MOZ_ASSERT(aOther.mSamples == 0,
+               "Don't use this ctor after AudioCallbackDriver::Init");
+    MOZ_ASSERT(aOther.mSampleWriteOffset == 1,
+               "Don't use this ctor after AudioCallbackDriver::Init");
+    MOZ_ASSERT(aOther.mChannels != 0);
+
+    mBuffer = nullptr;
+    mSamples = 0;
+    mSampleWriteOffset = 1;
+    mChannels = aOther.mChannels;
+
+    return *this;
+  }
+
+  /**
+   * Set the buffer in this wrapper. This is to be called at the beginning of
+   * the callback.
+   */
+  void SetBuffer(T* aBuffer, uint32_t aFrames) {
+    MOZ_ASSERT(!mBuffer && !mSamples, "SetBuffer called twice.");
+    mBuffer = aBuffer;
+    mSamples = FramesToSamples(mChannels, aFrames);
+    mSampleWriteOffset = 0;
+  }
+
+  /**
+   * Write some frames to the internal buffer. Free space in the buffer should
+   * be check prior to calling this.
+   */
+  void WriteFrames(T* aBuffer, uint32_t aFrames) {
+    MOZ_ASSERT(aFrames <= Available(),
+               "Writing more that we can in the audio buffer.");
+
+    PodCopy(mBuffer + mSampleWriteOffset, aBuffer,
+            FramesToSamples(mChannels, aFrames));
+    mSampleWriteOffset += FramesToSamples(mChannels, aFrames);
+  }
+
+  /**
+   * Number of frames that can be written to the buffer.
+   */
+  uint32_t Available() {
+    return SamplesToFrames(mChannels, mSamples - mSampleWriteOffset);
+  }
+
+  /**
+   * Check that the buffer is completly filled, and reset internal state so this
+   * instance can be reused.
+   */
+  void BufferFilled() {
+    MOZ_ASSERT(Available() == 0, "Frames should have been written");
+    MOZ_ASSERT(mSamples, "Buffer not set.");
+    mSamples = 0;
+    mSampleWriteOffset = 0;
+    mBuffer = nullptr;
+  }
+
+ private:
+  /* This is not an owned pointer, but the pointer passed to use via the audio
+   * callback. */
+  T* mBuffer;
+  /* The number of samples of this audio buffer. */
+  uint32_t mSamples;
+  /* The position at which new samples should be written. We want to return to
+   * the audio callback iff this is equal to mSamples. */
+  uint32_t mSampleWriteOffset;
+  uint32_t mChannels;
+};
+
+/**
+ * This is a class that interfaces with the AudioCallbackBufferWrapper, and is
+ * responsible for storing the excess of data produced by the MediaTrackGraph
+ * because of different rounding constraints, to be used the next time the audio
+ * backend calls back.
+ */
+template <typename T, uint32_t BLOCK_SIZE>
+class SpillBuffer {
+ public:
+  SpillBuffer() : mBuffer(nullptr), mPosition(0), mChannels(0) {}
+
+  explicit SpillBuffer(uint32_t aChannels)
+      : mPosition(0), mChannels(aChannels) {
+    MOZ_ASSERT(aChannels);
+    mBuffer = MakeUnique<T[]>(BLOCK_SIZE * mChannels);
+    PodZero(mBuffer.get(), BLOCK_SIZE * mChannels);
+  }
+
+  SpillBuffer& operator=(SpillBuffer& aOther) {
+    MOZ_ASSERT(aOther.mPosition == 0,
+               "Don't use this ctor after AudioCallbackDriver::Init");
+    MOZ_ASSERT(aOther.mChannels != 0);
+    MOZ_ASSERT(aOther.mBuffer);
+
+    mPosition = aOther.mPosition;
+    mChannels = aOther.mChannels;
+    mBuffer = std::move(aOther.mBuffer);
+
+    return *this;
+  }
+
+  SpillBuffer& operator=(SpillBuffer&& aOther) {
+    return this->operator=(aOther);
+  }
+
+  /* Empty the spill buffer into the buffer of the audio callback. This returns
+   * the number of frames written. */
+  uint32_t Empty(AudioCallbackBufferWrapper<T>& aBuffer) {
+    uint32_t framesToWrite =
+        std::min(aBuffer.Available(), SamplesToFrames(mChannels, mPosition));
+
+    aBuffer.WriteFrames(mBuffer.get(), framesToWrite);
+
+    mPosition -= FramesToSamples(mChannels, framesToWrite);
+    // If we didn't empty the spill buffer for some reason, shift the remaining
+    // data down
+    if (mPosition > 0) {
+      MOZ_ASSERT(FramesToSamples(mChannels, framesToWrite) + mPosition <=
+                 BLOCK_SIZE * mChannels);
+      PodMove(mBuffer.get(),
+              mBuffer.get() + FramesToSamples(mChannels, framesToWrite),
+              mPosition);
+    }
+
+    return framesToWrite;
+  }
+  /* Fill the spill buffer from aInput, containing aFrames frames, return the
+   * number of frames written to the spill buffer */
+  uint32_t Fill(T* aInput, uint32_t aFrames) {
+    uint32_t framesToWrite =
+        std::min(aFrames, BLOCK_SIZE - SamplesToFrames(mChannels, mPosition));
+
+    MOZ_ASSERT(FramesToSamples(mChannels, framesToWrite) + mPosition <=
+               BLOCK_SIZE * mChannels);
+    PodCopy(mBuffer.get() + mPosition, aInput,
+            FramesToSamples(mChannels, framesToWrite));
+
+    mPosition += FramesToSamples(mChannels, framesToWrite);
+
+    return framesToWrite;
+  }
+
+ private:
+  /* The spilled data. */
+  UniquePtr<T[]> mBuffer;
+  /* The current write position, in samples, in the buffer when filling, or the
+   * amount of buffer filled when emptying. */
+  uint32_t mPosition;
+  uint32_t mChannels;
+};
+
+}  // namespace mozilla
+
+#endif  // MOZILLA_SCRATCHBUFFER_H_