third_party/WebKit/Source/platform/audio/AudioDelayDSPKernel.cpp

/*
 * Copyright (C) 2010, Google Inc. All rights reserved.
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#include "platform/audio/AudioDelayDSPKernel.h"

#include <cmath>
#include "platform/audio/AudioUtilities.h"
#include "platform/wtf/MathExtras.h"

namespace blink {

const float kSmoothingTimeConstant = 0.020f;  // 20ms

AudioDelayDSPKernel::AudioDelayDSPKernel(AudioDSPKernelProcessor* processor,
                                         size_t processing_size_in_frames)
    : AudioDSPKernel(processor),
      write_index_(0),
      first_time_(true),
      delay_times_(processing_size_in_frames) {}

AudioDelayDSPKernel::AudioDelayDSPKernel(double max_delay_time,
                                         float sample_rate)
    : AudioDSPKernel(sample_rate),
      max_delay_time_(max_delay_time),
      write_index_(0),
      first_time_(true) {
  DCHECK_GT(max_delay_time, 0.0);
  DCHECK(!std::isnan(max_delay_time));
  if (max_delay_time <= 0.0 || std::isnan(max_delay_time))
    return;

  size_t buffer_length = BufferLengthForDelay(max_delay_time, sample_rate);
  DCHECK(buffer_length);
  if (!buffer_length)
    return;

  buffer_.Allocate(buffer_length);
  buffer_.Zero();

  smoothing_rate_ = AudioUtilities::DiscreteTimeConstantForSampleRate(
      kSmoothingTimeConstant, sample_rate);
}

size_t AudioDelayDSPKernel::BufferLengthForDelay(double max_delay_time,
                                                 double sample_rate) const {
  // Compute the length of the buffer needed to handle a max delay of
  // |maxDelayTime|. One is added to handle the case where the actual delay
  // equals the maximum delay.
  return 1 + AudioUtilities::TimeToSampleFrame(max_delay_time, sample_rate);
}

bool AudioDelayDSPKernel::HasSampleAccurateValues() {
  return false;
}

void AudioDelayDSPKernel::CalculateSampleAccurateValues(float*, size_t) {
  NOTREACHED();
}

double AudioDelayDSPKernel::DelayTime(float sample_rate) {
  return desired_delay_frames_ / sample_rate;
}

void AudioDelayDSPKernel::Process(const float* source,
                                  float* destination,
                                  size_t frames_to_process) {
  size_t buffer_length = buffer_.size();
  float* buffer = buffer_.Data();

  DCHECK(buffer_length);
  if (!buffer_length)
    return;

  DCHECK(source);
  DCHECK(destination);
  if (!source || !destination)
    return;

  float sample_rate = this->SampleRate();
  double delay_time = 0;
  float* delay_times = delay_times_.Data();
  double max_time = MaxDelayTime();

  bool sample_accurate = HasSampleAccurateValues();

  if (sample_accurate) {
    CalculateSampleAccurateValues(delay_times, frames_to_process);
  } else {
    delay_time = this->DelayTime(sample_rate);

    // Make sure the delay time is in a valid range.
    delay_time = clampTo(delay_time, 0.0, max_time);

    if (first_time_) {
      current_delay_time_ = delay_time;
      first_time_ = false;
    }
  }

  for (unsigned i = 0; i < frames_to_process; ++i) {
    if (sample_accurate) {
      delay_time = delay_times[i];
      if (std::isnan(delay_time))
        delay_time = max_time;
      else
        delay_time = clampTo(delay_time, 0.0, max_time);
      current_delay_time_ = delay_time;
    } else {
      // Approach desired delay time.
      current_delay_time_ +=
          (delay_time - current_delay_time_) * smoothing_rate_;
    }

    double desired_delay_frames = current_delay_time_ * sample_rate;

    double read_position = write_index_ + buffer_length - desired_delay_frames;
    if (read_position >= buffer_length)
      read_position -= buffer_length;

    // Linearly interpolate in-between delay times.
    int read_index1 = static_cast<int>(read_position);
    int read_index2 = (read_index1 + 1) % buffer_length;
    double interpolation_factor = read_position - read_index1;

    double input = static_cast<float>(*source++);
    buffer[write_index_] = static_cast<float>(input);
    write_index_ = (write_index_ + 1) % buffer_length;

    double sample1 = buffer[read_index1];
    double sample2 = buffer[read_index2];

    double output =
        (1.0 - interpolation_factor) * sample1 + interpolation_factor * sample2;

    *destination++ = static_cast<float>(output);
  }
}

void AudioDelayDSPKernel::Reset() {
  first_time_ = true;
  buffer_.Zero();
}

double AudioDelayDSPKernel::TailTime() const {
  // Account for worst case delay.
  // Don't try to track actual delay time which can change dynamically.
  return max_delay_time_;
}

double AudioDelayDSPKernel::LatencyTime() const {
  return 0;
}

}  // namespace blink