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diff --git a/WebCore/webaudio/AudioNodeOutput.h b/WebCore/webaudio/AudioNodeOutput.h
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+/*
+ * Copyright (C) 2010, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1.  Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2.  Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef AudioNodeOutput_h
+#define AudioNodeOutput_h
+
+#include "AudioBus.h"
+#include "AudioNode.h"
+#include <wtf/HashSet.h>
+#include <wtf/OwnPtr.h>
+#include <wtf/Vector.h>
+
+namespace WebCore {
+
+class AudioContext;
+class AudioNodeInput;
+
+// AudioNodeOutput represents a single output for an AudioNode.
+// It may be connected to one or more AudioNodeInputs.
+
+class AudioNodeOutput {
+public:
+    // It's OK to pass 0 for numberOfChannels in which case setNumberOfChannels() must be called later on.
+    AudioNodeOutput(AudioNode*, unsigned numberOfChannels);
+
+    // Can be called from any thread.
+    AudioNode* node() const { return m_node; }
+    AudioContext* context() { return m_node->context(); }
+    
+    // Causes our AudioNode to process if it hasn't already for this render quantum.
+    // It returns the bus containing the processed audio for this output, returning inPlaceBus if in-place processing was possible.
+    // Called from context's audio thread.
+    AudioBus* pull(AudioBus* inPlaceBus, size_t framesToProcess);
+
+    // bus() will contain the rendered audio after pull() is called for each rendering time quantum.
+    // Called from context's audio thread.
+    AudioBus* bus() const;
+
+    // fanOutCount() is the number of AudioNodeInputs that we're connected to.
+    // This function should not be called in audio thread rendering code, instead renderingFanOutCount() should be used.
+    // It must be called with the context's graph lock.
+    unsigned fanOutCount();
+
+    // renderingFanOutCount() is the number of AudioNodeInputs that we're connected to during rendering.
+    // Unlike fanOutCount() it will not change during the course of a render quantum.
+    unsigned renderingFanOutCount() const;
+
+    // It must be called with the context's graph lock.
+    void disconnectAllInputs();
+
+    void setNumberOfChannels(unsigned);
+    unsigned numberOfChannels() const { return m_numberOfChannels; }
+    bool isChannelCountKnown() const { return numberOfChannels() > 0; }
+
+    // Disable/Enable happens when there are still JavaScript references to a node, but it has otherwise "finished" its work.
+    // For example, when a note has finished playing.  It is kept around, because it may be played again at a later time.
+    // They must be called with the context's graph lock.
+    void disable();
+    void enable();
+
+    // updateRenderingState() is called in the audio thread at the start or end of the render quantum to handle any recent changes to the graph state.
+    // It must be called with the context's graph lock.
+    void updateRenderingState();
+    
+private:
+    AudioNode* m_node;
+
+    friend class AudioNodeInput;
+    
+    // These are called from AudioNodeInput.
+    // They must be called with the context's graph lock.
+    void addInput(AudioNodeInput*);
+    void removeInput(AudioNodeInput*);
+
+    // setInternalBus() sets m_internalOutputBus appropriately for the number of channels.
+    // It is called in the constructor or in the audio thread with the context's graph lock.
+    void setInternalBus();
+
+    // Announce to any nodes we're connected to that we changed our channel count for its input.
+    // It must be called in the audio thread with the context's graph lock.
+    void propagateChannelCount();
+
+    // updateNumberOfChannels() is called in the audio thread at the start or end of the render quantum to pick up channel changes.
+    // It must be called with the context's graph lock.
+    void updateNumberOfChannels();
+
+    // m_numberOfChannels will only be changed in the audio thread.
+    // The main thread sets m_desiredNumberOfChannels which will later get picked up in the audio thread in updateNumberOfChannels().
+    unsigned m_numberOfChannels;
+    unsigned m_desiredNumberOfChannels;
+    
+    // m_internalOutputBus will point to either m_monoInternalBus or m_stereoInternalBus.
+    // It must only be changed in the audio thread (or constructor).
+    AudioBus* m_internalOutputBus;
+    OwnPtr<AudioBus> m_monoInternalBus;
+    OwnPtr<AudioBus> m_stereoInternalBus;
+
+    // m_actualDestinationBus is set in pull() and will either point to one of our internal busses or to the in-place bus.
+    // It must only be changed in the audio thread (or constructor).
+    AudioBus* m_actualDestinationBus;
+
+    HashSet<AudioNodeInput*> m_inputs;
+    typedef HashSet<AudioNodeInput*>::iterator InputsIterator;
+    bool m_isEnabled;
+    
+    // For the purposes of rendering, keeps track of the number of inputs we're connected to.
+    // This value should only be changed at the very start or end of the rendering quantum.
+    unsigned m_renderingFanOutCount;
+};
+
+} // namespace WebCore
+
+#endif // AudioNodeOutput_h