1 files changed, 83 insertions, 0 deletions
diff --git a/dom/media/webrtc/SineWaveGenerator.h b/dom/media/webrtc/SineWaveGenerator.h
new file mode 100644
index 0000000000..d30ccf448f
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+++ b/dom/media/webrtc/SineWaveGenerator.h
@@ -0,0 +1,83 @@
+/* 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_ */