74 lines
2.7 KiB
C++
74 lines
2.7 KiB
C++
/*
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* Copyright (C) 2013 Google Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of Apple Inc. ("Apple") nor the names of
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* its contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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* LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef DownSampler_h
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#define DownSampler_h
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#include "AudioArray.h"
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#include "DirectConvolver.h"
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namespace WebCore {
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// DownSampler down-samples the source stream by a factor of 2x.
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class DownSampler final {
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WTF_MAKE_FAST_ALLOCATED;
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public:
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explicit DownSampler(size_t inputBlockSize);
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// The destination buffer |destP| is of size sourceFramesToProcess / 2.
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void process(const float* sourceP, float* destP, size_t sourceFramesToProcess);
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void reset();
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// Latency based on the destination sample-rate.
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size_t latencyFrames() const;
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private:
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enum { DefaultKernelSize = 256 };
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size_t m_inputBlockSize;
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// Computes ideal band-limited half-band filter coefficients.
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// In other words, filter out all frequencies higher than 0.25 * Nyquist.
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void initializeKernel();
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AudioFloatArray m_reducedKernel { DefaultKernelSize / 2 };
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// Half-band filter.
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DirectConvolver m_convolver;
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AudioFloatArray m_tempBuffer;
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// Used as delay-line (FIR filter history) for the input samples to account for the 0.5 term right in the middle of the kernel.
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AudioFloatArray m_inputBuffer;
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};
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} // namespace WebCore
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#endif // DownSampler_h
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