Index: Source/core/platform/audio/UpSampler.cpp |
diff --git a/Source/core/platform/audio/UpSampler.cpp b/Source/core/platform/audio/UpSampler.cpp |
new file mode 100644 |
index 0000000000000000000000000000000000000000..cb69747c9fdd4dd534ebbf151a7250806a4dc179 |
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+++ b/Source/core/platform/audio/UpSampler.cpp |
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+/* |
+ * Copyright (C) 2013 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 "config.h" |
+ |
+#if ENABLE(WEB_AUDIO) |
+ |
+#include "core/platform/audio/UpSampler.h" |
+ |
+#include "wtf/MathExtras.h" |
+ |
+namespace WebCore { |
+ |
+UpSampler::UpSampler(size_t inputBlockSize) |
+ : m_inputBlockSize(inputBlockSize) |
+ , m_kernel(DefaultKernelSize) |
+ , m_tempBuffer(inputBlockSize) |
+ , m_inputBuffer(inputBlockSize * 2) |
+ , m_convolver(inputBlockSize) |
+{ |
+ initializeKernel(); |
+} |
+ |
+void UpSampler::initializeKernel() |
+{ |
+ // Blackman window parameters. |
+ double alpha = 0.16; |
+ double a0 = 0.5 * (1.0 - alpha); |
+ double a1 = 0.5; |
+ double a2 = 0.5 * alpha; |
+ |
+ int n = m_kernel.size(); |
+ int halfSize = n / 2; |
+ double subsampleOffset = -0.5; |
+ |
+ for (int i = 0; i < n; ++i) { |
+ // Compute the sinc() with offset. |
+ double s = piDouble * (i - halfSize - subsampleOffset); |
+ double sinc = !s ? 1.0 : sin(s) / s; |
+ |
+ // Compute Blackman window, matching the offset of the sinc(). |
+ double x = (i - subsampleOffset) / n; |
+ double window = a0 - a1 * cos(2.0 * piDouble * x) + a2 * cos(4.0 * piDouble * x); |
+ |
+ // Window the sinc() function. |
+ m_kernel[i] = sinc * window; |
+ } |
+} |
+ |
+void UpSampler::process(const float* sourceP, float* destP, size_t sourceFramesToProcess) |
+{ |
+ ASSERT(sourceFramesToProcess == m_tempBuffer.size()); |
+ if (sourceFramesToProcess != m_tempBuffer.size()) |
+ return; |
+ |
+ // Copy source samples to 2nd half of input buffer. |
+ float* inputP = m_inputBuffer.data() + m_inputBlockSize; |
+ memcpy(inputP, sourceP, sizeof(float) * sourceFramesToProcess); |
+ |
+ int halfSize = m_kernel.size() / 2; |
+ |
+ // Copy even sample-frames 0,2,4,6... (delayed by the linear phase delay) directly into destP. |
+ for (unsigned i = 0; i < sourceFramesToProcess; ++i) |
+ destP[i * 2] = inputP[i - halfSize]; |
Ken Russell (switch to Gerrit)
2013/05/23 02:29:25
Checks and assertions are needed to ensure that "i
Chris Rogers
2013/05/24 20:09:04
Done.
|
+ |
+ // Compute odd sample-frames 1,3,5,7... |
+ float* oddSamplesP = m_tempBuffer.data(); |
+ m_convolver.process(&m_kernel, sourceP, oddSamplesP, sourceFramesToProcess); |
+ |
+ for (unsigned i = 0; i < sourceFramesToProcess; ++i) |
+ destP[i * 2 + 1] = oddSamplesP[i]; |
+ |
+ // Copy 2nd half of input buffer to 1st half. |
+ memcpy(m_inputBuffer.data(), inputP, sizeof(float) * sourceFramesToProcess); |
Ken Russell (switch to Gerrit)
2013/05/23 02:29:25
Again could you please explain to me why m_inputBu
Chris Rogers
2013/05/24 20:09:04
Added comment in header file.
|
+} |
+ |
+void UpSampler::reset() |
+{ |
+ m_convolver.reset(); |
+ m_inputBuffer.zero(); |
+} |
+ |
+size_t UpSampler::latencyFrames() const |
+{ |
+ // Divide by two since this is a linear phase kernel and the delay is at the center of the kernel. |
+ return m_kernel.size() / 2; |
+} |
+ |
+} // namespace WebCore |
+ |
+#endif // ENABLE(WEB_AUDIO) |