1 files changed, 107 insertions, 0 deletions
diff --git a/dom/media/webaudio/blink/HRTFKernel.cpp b/dom/media/webaudio/blink/HRTFKernel.cpp
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index 000000000..3ee5e63a3
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+++ b/dom/media/webaudio/blink/HRTFKernel.cpp
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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.
+ * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of
+ *     its contributors may be used to endorse or promote products derived
+ *     from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE 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 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.
+ */
+
+#include "HRTFKernel.h"
+namespace WebCore {
+
+// Takes the input audio channel |impulseP| as an input impulse response and calculates the average group delay.
+// This represents the initial delay before the most energetic part of the impulse response.
+// The sample-frame delay is removed from the |impulseP| impulse response, and this value  is returned.
+// The |length| of the passed in |impulseP| must be must be a power of 2.
+static float extractAverageGroupDelay(float* impulseP, size_t length)
+{
+    // Check for power-of-2.
+    MOZ_ASSERT(length && (length & (length - 1)) == 0);
+
+    FFTBlock estimationFrame(length);
+    estimationFrame.PerformFFT(impulseP);
+
+    float frameDelay = static_cast<float>(estimationFrame.ExtractAverageGroupDelay());
+    estimationFrame.GetInverse(impulseP);
+
+    return frameDelay;
+}
+
+HRTFKernel::HRTFKernel(float* impulseResponse, size_t length, float sampleRate)
+    : m_frameDelay(0)
+    , m_sampleRate(sampleRate)
+{
+    AlignedTArray<float> buffer;
+    // copy to a 32-byte aligned buffer
+    if (((uintptr_t)impulseResponse & 31) != 0) {
+      buffer.SetLength(length);
+      mozilla::PodCopy(buffer.Elements(), impulseResponse, length);
+      impulseResponse = buffer.Elements();
+    }
+
+    // Determine the leading delay (average group delay) for the response.
+    m_frameDelay = extractAverageGroupDelay(impulseResponse, length);
+
+    // The FFT size (with zero padding) needs to be twice the response length
+    // in order to do proper convolution.
+    unsigned fftSize = 2 * length;
+
+    // Quick fade-out (apply window) at truncation point
+    // because the impulse response has been truncated.
+    unsigned numberOfFadeOutFrames = static_cast<unsigned>(sampleRate / 4410); // 10 sample-frames @44.1KHz sample-rate
+    MOZ_ASSERT(numberOfFadeOutFrames < length);
+    if (numberOfFadeOutFrames < length) {
+        for (unsigned i = length - numberOfFadeOutFrames; i < length; ++i) {
+            float x = 1.0f - static_cast<float>(i - (length - numberOfFadeOutFrames)) / numberOfFadeOutFrames;
+            impulseResponse[i] *= x;
+        }
+    }
+
+    m_fftFrame = new FFTBlock(fftSize);
+    m_fftFrame->PadAndMakeScaledDFT(impulseResponse, length);
+}
+
+// Interpolates two kernels with x: 0 -> 1 and returns the result.
+nsReturnRef<HRTFKernel> HRTFKernel::createInterpolatedKernel(HRTFKernel* kernel1, HRTFKernel* kernel2, float x)
+{
+    MOZ_ASSERT(kernel1 && kernel2);
+    if (!kernel1 || !kernel2)
+        return nsReturnRef<HRTFKernel>();
+
+    MOZ_ASSERT(x >= 0.0 && x < 1.0);
+    x = mozilla::clamped(x, 0.0f, 1.0f);
+
+    float sampleRate1 = kernel1->sampleRate();
+    float sampleRate2 = kernel2->sampleRate();
+    MOZ_ASSERT(sampleRate1 == sampleRate2);
+    if (sampleRate1 != sampleRate2)
+        return nsReturnRef<HRTFKernel>();
+
+    float frameDelay = (1 - x) * kernel1->frameDelay() + x * kernel2->frameDelay();
+
+    nsAutoPtr<FFTBlock> interpolatedFrame(
+        FFTBlock::CreateInterpolatedBlock(*kernel1->fftFrame(), *kernel2->fftFrame(), x));
+    return HRTFKernel::create(interpolatedFrame, frameDelay, sampleRate1);
+}
+
+} // namespace WebCore