Source/platform/audio/UpSampler.h

/*
 * Copyright (C) 2013 Google Inc. All rights reserved.
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#ifndef UpSampler_h
#define UpSampler_h

#include "platform/audio/AudioArray.h"
#include "platform/audio/DirectConvolver.h"

namespace WebCore {

// UpSampler up-samples the source stream by a factor of 2x.

class PLATFORM_EXPORT UpSampler {
public:
    UpSampler(size_t inputBlockSize);

    // The destination buffer |destP| is of size sourceFramesToProcess * 2.
    void process(const float* sourceP, float* destP, size_t sourceFramesToProcess);

    void reset();

    // Latency based on the source sample-rate.
    size_t latencyFrames() const;

private:
    enum { DefaultKernelSize = 128 };

    size_t m_inputBlockSize;

    // Computes ideal band-limited filter coefficients to sample in between each source sample-frame.
    // This filter will be used to compute the odd sample-frames of the output.
    void initializeKernel();
    AudioFloatArray m_kernel;

    // Computes the odd sample-frames of the output.
    DirectConvolver m_convolver;

    AudioFloatArray m_tempBuffer;

    // Delay line for generating the even sample-frames of the output.
    // The source samples are delayed exactly to match the linear phase delay of the FIR filter (convolution)
    // used to generate the odd sample-frames of the output.
    AudioFloatArray m_inputBuffer;
};

} // namespace WebCore

#endif // UpSampler_h