Common: Add a NullAudioStream implementation

src/common/null_audio_stream.h

@@ -0,0 +1,17 @@
+#pragma once
+#include "audio_stream.h"
+
+class NullAudioStream final : public AudioStream
+{
+public:
+  NullAudioStream();
+  ~NullAudioStream();
+
+  static std::unique_ptr<AudioStream> Create();
+
+protected:
+  bool OpenDevice() override;
+  void PauseDevice(bool paused) override;
+  void CloseDevice() override;
+  void BufferAvailable() override;
+};