Support for AudioContextOptions latencyHint.

third_party/WebKit/Source/platform/audio/AudioDestination.cpp

 /*
  * 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
@@ skipping 16 matching lines @@
  */
 
 #include "platform/audio/AudioDestination.h"
 
 #include "platform/Histogram.h"
 #include "platform/audio/AudioFIFO.h"
 #include "platform/audio/AudioPullFIFO.h"
 #include "platform/audio/AudioUtilities.h"
 #include "platform/weborigin/SecurityOrigin.h"
 #include "public/platform/Platform.h"
+#include "public/platform/WebAudioLatencyHint.h"
 #include "public/platform/WebSecurityOrigin.h"
 #include "wtf/PtrUtil.h"
 #include <memory>
 
 namespace blink {
 
 // Size of the FIFO
 const size_t fifoSize = 8192;
 
 // Factory method: Chromium-implementation
 std::unique_ptr<AudioDestination> AudioDestination::create(
     AudioIOCallback& callback,
     const String& inputDeviceId,
     unsigned numberOfInputChannels,
     unsigned numberOfOutputChannels,
-    float sampleRate,
+    const WebAudioLatencyHint& latencyHint,
     PassRefPtr<SecurityOrigin> securityOrigin) {
   return wrapUnique(new AudioDestination(
       callback, inputDeviceId, numberOfInputChannels, numberOfOutputChannels,
-      sampleRate, std::move(securityOrigin)));
+      latencyHint, std::move(securityOrigin)));
 }
 
 AudioDestination::AudioDestination(AudioIOCallback& callback,
                                    const String& inputDeviceId,
                                    unsigned numberOfInputChannels,
                                    unsigned numberOfOutputChannels,
-                                   float sampleRate,
+                                   const WebAudioLatencyHint& latencyHint,
                                    PassRefPtr<SecurityOrigin> securityOrigin)
     : m_callback(callback),
       m_numberOfOutputChannels(numberOfOutputChannels),
       m_inputBus(AudioBus::create(numberOfInputChannels,
                                   AudioUtilities::kRenderQuantumFrames)),
       m_renderBus(AudioBus::create(numberOfOutputChannels,
                                    AudioUtilities::kRenderQuantumFrames,
                                    false)),
-      m_sampleRate(sampleRate),
       m_isPlaying(false) {
   // Histogram for audioHardwareBufferSize
   DEFINE_STATIC_LOCAL(SparseHistogram, hardwareBufferSizeHistogram,
                       ("WebAudio.AudioDestination.HardwareBufferSize"));
   // Histogram for the actual callback size used.  Typically, this is the same
   // as audioHardwareBufferSize, but can be adjusted depending on some
   // heuristics below.
   DEFINE_STATIC_LOCAL(SparseHistogram, callbackBufferSizeHistogram,
                       ("WebAudio.AudioDestination.CallbackBufferSize"));
 
-  // Use the optimal buffer size recommended by the audio backend.
-  size_t recommendedHardwareBufferSize =
-      Platform::current()->audioHardwareBufferSize();
-  m_callbackBufferSize = recommendedHardwareBufferSize;
+  m_audioDevice = wrapUnique(Platform::current()->createAudioDevice(
+      numberOfInputChannels, numberOfOutputChannels, latencyHint, this,
+      inputDeviceId, std::move(securityOrigin)));
+  DCHECK(m_audioDevice);
 
-#if OS(ANDROID)
-  // The optimum low-latency hardware buffer size is usually too small on
-  // Android for WebAudio to render without glitching. So, if it is small, use
-  // a larger size. If it was already large, use the requested size.
-  //
-  // Since WebAudio renders in 128-frame blocks, the small buffer sizes (144
-  // for a Galaxy Nexus), cause significant processing jitter. Sometimes
-  // multiple blocks will processed, but other times will not be since the FIFO
-  // can satisfy the request. By using a larger callbackBufferSize, we smooth
-  // out the jitter.
-  const size_t kSmallBufferSize = 1024;
-  const size_t kDefaultCallbackBufferSize = 2048;
-
-  if (m_callbackBufferSize <= kSmallBufferSize)
-    m_callbackBufferSize = kDefaultCallbackBufferSize;
-#endif
-
+  m_callbackBufferSize = m_audioDevice->framesPerBuffer();
   // Quick exit if the requested size is too large.
   DCHECK_LE(m_callbackBufferSize + AudioUtilities::kRenderQuantumFrames,
             fifoSize);
   if (m_callbackBufferSize + AudioUtilities::kRenderQuantumFrames > fifoSize)
     return;
 
-  m_audioDevice = wrapUnique(Platform::current()->createAudioDevice(
-      m_callbackBufferSize, numberOfInputChannels, numberOfOutputChannels,
-      sampleRate, this, inputDeviceId, std::move(securityOrigin)));
-  ASSERT(m_audioDevice);
-
   // Record the sizes if we successfully created an output device.
-  hardwareBufferSizeHistogram.sample(recommendedHardwareBufferSize);
+  hardwareBufferSizeHistogram.sample(
+      Platform::current()->audioHardwareBufferSize());
   callbackBufferSizeHistogram.sample(m_callbackBufferSize);

[o1ka, 2016/12/07 20:56:01]

rtoy@ - callback buffer size will be different for different latencies, won't
this histogram loose its meaning?
Is WebAudio interested in a separate histogram for each latency (keeping the
existing one for Interactive)?

[Raymond Toy, 2016/12/08 16:24:50]

Good point. It probably would be a good idea to add two more histograms to keep
track of the categories.  And an additional two more, maybe, to keep track of
the requested float latency and the actual value.

But we don't need to block this CL for that.  We have time to do that later. 

 
   // Create a FIFO to handle the possibility of the callback size
   // not being a multiple of the render size. If the FIFO already
   // contains enough data, the data will be provided directly.
   // Otherwise, the FIFO will call the provider enough times to
   // satisfy the request for data.
   m_fifo = wrapUnique(new AudioPullFIFO(*this, numberOfOutputChannels, fifoSize,
                                         AudioUtilities::kRenderQuantumFrames));
 
   // Input buffering.
@@ skipping 70 matching lines @@
   AudioBus* sourceBus = nullptr;
   if (m_inputFifo->framesInFifo() >= framesToProcess) {
     m_inputFifo->consume(m_inputBus.get(), framesToProcess);
     sourceBus = m_inputBus.get();
   }
 
   m_callback.render(sourceBus, bus, framesToProcess);
 }
 
 }  // namespace blink