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/* 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
template <typename Sample>
class SineWaveGenerator {
static_assert(std::is_same<Sample, int16_t>::value ||
std::is_same<Sample, float>::value);
public:
static const int bytesPerSample = sizeof(Sample);
static const int millisecondsPerSecond = PR_MSEC_PER_SEC;
/* If more than 1 channel, generated samples are interleaved. */
SineWaveGenerator(uint32_t aSampleRate, uint32_t aFrequency,
uint32_t aChannels = 1)
: mTotalLength(aSampleRate * aChannels / aFrequency), mReadLength(0) {
MOZ_ASSERT(aChannels >= 1);
// 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<Sample[]>(mTotalLength);
for (uint32_t i = 0; i < aSampleRate / aFrequency; ++i) {
for (uint32_t j = 0; j < aChannels; ++j) {
mAudioBuffer[i * aChannels + j] =
Amplitude() * sin(2 * M_PI * i * aChannels / mTotalLength);
}
}
}
// NOTE: only safely called from a single thread (MTG callback)
void generate(Sample* 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;
}
}
}
void SetOffset(TrackTicks aFrames) { mReadLength = aFrames % mTotalLength; }
TrackTicks Offset() const { return mReadLength; }
static float Amplitude() {
// Set volume to -20db.
if (std::is_same<Sample, int16_t>::value) {
return 3276.8; // 32768.0 * 10^(-20/20) = 3276.8
}
return 0.1f; // 1.0 * 10^(-20/20) = 0.1
}
private:
UniquePtr<Sample[]> mAudioBuffer;
TrackTicks mTotalLength;
TrackTicks mReadLength;
};
} // namespace mozilla
#endif /* SINEWAVEGENERATOR_H_ */