AnalyserNode should downmix channels to mono.

third_party/WebKit/Source/modules/webaudio/RealtimeAnalyser.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
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 29 matching lines @@
 
 const unsigned RealtimeAnalyser::DefaultFFTSize = 2048;
 // All FFT implementations are expected to handle power-of-two sizes MinFFTSize <= size <= MaxFFTSize.
 const unsigned RealtimeAnalyser::MinFFTSize = 32;
 const unsigned RealtimeAnalyser::MaxFFTSize = 32768;
 const unsigned RealtimeAnalyser::InputBufferSize = RealtimeAnalyser::MaxFFTSize * 2;
 
 RealtimeAnalyser::RealtimeAnalyser()
     : m_inputBuffer(InputBufferSize)
     , m_writeIndex(0)
+    , m_downMixBus(AudioBus::create(1, AudioUtilities::kRenderQuantumFrames))
     , m_fftSize(DefaultFFTSize)
     , m_magnitudeBuffer(DefaultFFTSize / 2)
     , m_smoothingTimeConstant(DefaultSmoothingTimeConstant)
     , m_minDecibels(DefaultMinDecibels)
     , m_maxDecibels(DefaultMaxDecibels)
     , m_lastAnalysisTime(-1)
 {
     m_analysisFrame = adoptPtr(new FFTFrame(DefaultFFTSize));
 }
 
@@ skipping 25 matching lines @@
     if (!isBusGood)
         return;
 
     // FIXME : allow to work with non-FFTSize divisible chunking
     bool isDestinationGood = m_writeIndex < m_inputBuffer.size() && m_writeIndex + framesToProcess <= m_inputBuffer.size();
     ASSERT(isDestinationGood);
     if (!isDestinationGood)
         return;
 
     // Perform real-time analysis
-    const float* source = bus->channel(0)->data();
     float* dest = m_inputBuffer.data() + m_writeIndex;
 
-    // The source has already been sanity checked with isBusGood above.
-    memcpy(dest, source, sizeof(float) * framesToProcess);
-
-    // Sum all channels in one if numberOfChannels > 1.
-    unsigned numberOfChannels = bus->numberOfChannels();
-    if (numberOfChannels > 1) {
-        for (unsigned i = 1; i < numberOfChannels; ++i) {
-            source = bus->channel(i)->data();
-            VectorMath::vadd(dest, 1, source, 1, dest, 1, framesToProcess);
-        }
-        const float scale =  1.0 / numberOfChannels;
-        VectorMath::vsmul(dest, 1, &scale, dest, 1, framesToProcess);
-    }
+    // Clear the bus and downmix the input according to the down mixing rules.  Then save the result
+    // in the m_inputBuffer at the appropriate place.
+    m_downMixBus->zero();
+    m_downMixBus->sumFrom(*bus);
+    memcpy(dest, m_downMixBus->channel(0)->data(), framesToProcess * sizeof(*dest));
 
     m_writeIndex += framesToProcess;
     if (m_writeIndex >= InputBufferSize)
         m_writeIndex = 0;
 }
 
 namespace {
 
 void applyWindow(float* p, size_t n)
 {
@@ skipping 205 matching lines @@
             if (scaledValue > UCHAR_MAX)
                 scaledValue = UCHAR_MAX;
 
             destination[i] = static_cast<unsigned char>(scaledValue);
         }
     }
 }
 
 } // namespace blink