VideoRecordingDemo: Make it work less pathetically on OSX and Windows.

It’s still crap, but a bit less than before:
- Pure video recording works well enough on OSX and Windows: On OSX,
both the H264 encoder and theoraenc work well. On Windows, H264
overloads the machine to the point of hanging Matlab, but theoraenc
works well enough.
- Video + Audio recording requires explicit definition of the
AudioSource and its properties, otherwise everything hangs completely.
However, even with that, audio recording works well, but video is
extremely choppy to the point of being almost useless.

-> So we have ok’ish video recording on Windows and OSX.
-> Painfully bad video+audio recording on Windows and OSX.
-> Perfect video and video+audio recording on Linux, at least last time
i checked.