Support for AudioContextOptions latencyHint.

third_party/WebKit/Source/modules/webaudio/AudioDestinationNode.h

 /*
  * 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
@@ skipping 21 matching lines @@
 #include "platform/audio/AudioIOCallback.h"
 #include "platform/audio/AudioSourceProvider.h"
 
 namespace blink {
 
 class AudioBus;
 class BaseAudioContext;
 
 class AudioDestinationHandler : public AudioHandler, public AudioIOCallback {
  public:
-  AudioDestinationHandler(AudioNode&, float sampleRate);
+  AudioDestinationHandler(AudioNode&);
   ~AudioDestinationHandler() override;
 
   // AudioHandler
   void process(size_t) final {
   }  // we're pulled by hardware so this is never called
 
   // The audio hardware calls render() to get the next render quantum of audio
   // into destinationBus.  It will optionally give us local/live audio input in
   // sourceBus (if it's not 0).
   void render(AudioBus* sourceBus,
               AudioBus* destinationBus,
               size_t numberOfFrames) final;
 
   size_t currentSampleFrame() const {
     return acquireLoad(&m_currentSampleFrame);
   }
   double currentTime() const {
     return currentSampleFrame() / static_cast<double>(sampleRate());

[o1ka, 2016/12/02 12:02:13]

What behavior we prefer in case sampleRate() is zero?

[Raymond Toy, 2016/12/02 16:57:45]

I believe this is safe, and infinity is ok.

This is should only be called from context()->currentTime(), and only if the
AudioDestinationNode is still active.  And if it is, sampleRate would not be 0.

   }
 
   virtual unsigned long maxChannelCount() const { return 0; }
 
   virtual void startRendering() = 0;
   virtual void stopRendering() = 0;
 
+  virtual double sampleRate() const = 0;
+  virtual int framesPerBuffer() const = 0;

[hongchan, 2016/12/02 17:40:12]

What does this mean? Isn't it same with the 'render quantum' size? Or is it the
platform-dependent batch process size? Please make a comment.

[Andrew MacPherson, 2016/12/05 14:12:53]

This is the buffer size in frames used by the underlying audio hardware, we
should see this value changing based on the different latencyHint values. I've
now added a comment but as rtoy@ also asked about this would a different name
work better here? audioBufferSize()?

+
  protected:
   // LocalAudioInputProvider allows us to expose an AudioSourceProvider for
   // local/live audio input.  If there is local/live audio input, we call set()
   // with the audio input data every render quantum.
   class LocalAudioInputProvider final : public AudioSourceProvider {
    public:
     LocalAudioInputProvider()
         : m_sourceBus(AudioBus::create(
               2,
               AudioUtilities::kRenderQuantumFrames))  // FIXME: handle
@@ skipping 34 matching lines @@
 
   unsigned long maxChannelCount() const;
 
  protected:
   AudioDestinationNode(BaseAudioContext&);
 };
 
 }  // namespace blink
 
 #endif  // AudioDestinationNode_h