dom/media/webrtc/SineWaveGenerator.h
author Sylvestre Ledru <sledru@mozilla.com>
Mon, 19 Nov 2018 13:25:37 +0000
changeset 446960 0ceae9db9ec0be18daa1a279511ad305723185d4
parent 406270 df7b724956eb943a25b30f3f75204f8d8255c1d2
permissions -rw-r--r--
Bug 1204606 - Reformat of dom/media r=jya # skip-blame Differential Revision: https://phabricator.services.mozilla.com/D12251

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef SINEWAVEGENERATOR_H_
#define SINEWAVEGENERATOR_H_

#include "MediaSegment.h"

namespace mozilla {

// generate 1k sine wave per second
class SineWaveGenerator {
 public:
  static const int bytesPerSample = 2;
  static const int millisecondsPerSecond = PR_MSEC_PER_SEC;

  explicit SineWaveGenerator(uint32_t aSampleRate, uint32_t aFrequency)
      : mTotalLength(aSampleRate / aFrequency), mReadLength(0) {
    // If we allow arbitrary frequencies, there's no guarantee we won't get
    // rounded here We could include an error term and adjust for it in
    // generation; not worth the trouble
    // MOZ_ASSERT(mTotalLength * aFrequency == aSampleRate);
    mAudioBuffer = MakeUnique<int16_t[]>(mTotalLength);
    for (int i = 0; i < mTotalLength; i++) {
      // Set volume to -20db. It's from 32768.0 * 10^(-20/20) = 3276.8
      mAudioBuffer[i] = (3276.8f * sin(2 * M_PI * i / mTotalLength));
    }
  }

  // NOTE: only safely called from a single thread (MSG callback)
  void generate(int16_t* aBuffer, TrackTicks aLengthInSamples) {
    TrackTicks remaining = aLengthInSamples;

    while (remaining) {
      TrackTicks processSamples = 0;

      if (mTotalLength - mReadLength >= remaining) {
        processSamples = remaining;
      } else {
        processSamples = mTotalLength - mReadLength;
      }
      memcpy(aBuffer, &mAudioBuffer[mReadLength],
             processSamples * bytesPerSample);
      aBuffer += processSamples;
      mReadLength += processSamples;
      remaining -= processSamples;
      if (mReadLength == mTotalLength) {
        mReadLength = 0;
      }
    }
  }

 private:
  UniquePtr<int16_t[]> mAudioBuffer;
  TrackTicks mTotalLength;
  TrackTicks mReadLength;
};

}  // namespace mozilla

#endif /* SINEWAVEGENERATOR_H_ */