third_party/blink/renderer/platform/audio/down_sampler.h

/*
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#ifndef THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_DOWN_SAMPLER_H_
#define THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_DOWN_SAMPLER_H_

#include "base/macros.h"
#include "third_party/blink/renderer/platform/audio/audio_array.h"
#include "third_party/blink/renderer/platform/audio/simple_fft_convolver.h"
#include "third_party/blink/renderer/platform/wtf/allocator.h"

namespace blink {

// DownSampler down-samples the source stream by a factor of 2x.

class PLATFORM_EXPORT DownSampler {
  USING_FAST_MALLOC(DownSampler);

 public:
  explicit DownSampler(size_t input_block_size);

  // The destination buffer |destP| is of size sourceFramesToProcess / 2.
  void Process(const float* source_p,
               float* dest_p,
               size_t source_frames_to_process);

  void Reset();

  // Latency based on the destination sample-rate.
  size_t LatencyFrames() const;

 private:
  enum { kDefaultKernelSize = 256 };

  size_t input_block_size_;

  // Half-band filter. SimpleFFTConvolver is always faster than DirectConvolver.
  SimpleFFTConvolver convolver_;

  AudioFloatArray temp_buffer_;

  // 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.
  AudioFloatArray input_buffer_;

  DISALLOW_COPY_AND_ASSIGN(DownSampler);
};

}  // namespace blink

#endif  // THIRD_PARTY_BLINK_RENDERER_PLATFORM_AUDIO_DOWN_SAMPLER_H_