third_party/WebKit/Source/platform/audio/AudioResamplerKernel.h

/*
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. 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 INC. OR ITS CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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 */

#ifndef AudioResamplerKernel_h
#define AudioResamplerKernel_h

#include "platform/PlatformExport.h"
#include "platform/audio/AudioArray.h"
#include "wtf/Allocator.h"

namespace blink {

class AudioResampler;

// AudioResamplerKernel does resampling on a single mono channel.
// It uses a simple linear interpolation for good performance.

class PLATFORM_EXPORT AudioResamplerKernel {
  USING_FAST_MALLOC(AudioResamplerKernel);
  WTF_MAKE_NONCOPYABLE(AudioResamplerKernel);

 public:
  AudioResamplerKernel(AudioResampler*);

  // getSourcePointer() should be called each time before process() is called.
  // Given a number of frames to process (for subsequent call to process()), it
  // returns a pointer and numberOfSourceFramesNeeded where sample data should
  // be copied. This sample data provides the input to the resampler when
  // process() is called.  framesToProcess must be less than or equal to
  // MaxFramesToProcess.
  float* getSourcePointer(size_t framesToProcess,
                          size_t* numberOfSourceFramesNeeded);

  // process() resamples framesToProcess frames from the source into
  // destination.  Each call to process() must be preceded by a call to
  // getSourcePointer() so that source input may be supplied.  framesToProcess
  // must be less than or equal to MaxFramesToProcess.
  void process(float* destination, size_t framesToProcess);

  // Resets the processing state.
  void reset();

  static const size_t MaxFramesToProcess;

 private:
  double rate() const;

  AudioResampler* m_resampler;
  AudioFloatArray m_sourceBuffer;

  // This is a (floating point) read index on the input stream.
  double m_virtualReadIndex;

  // We need to have continuity from one call of process() to the next.
  // m_lastValues stores the last two sample values from the last call to
  // process().  m_fillIndex represents how many buffered samples we have which
  // can be as many as 2.  For the first call to process() (or after reset())
  // there will be no buffered samples.
  float m_lastValues[2];
  unsigned m_fillIndex;
};

}  // namespace blink

#endif  // AudioResamplerKernel_h