If you mean recording starts to stutter after 8-10 seconds, but it continues nevertheless, then that's ok. The final recording will be smooth. Your computer can't keep up, but LFS Record will just wait upon each frame until LFS is ready before proceeding to the next frame.
If you mean the recording really stops and does not continue, then that's a problem. So please let me know which it is.
Regarding sound; yeah like Morpha said it's not possible to record both video and sound at the same time. However, I've been thinking, it should be possible to record video separately and sound separately. In two recording passes. And then you can merge the two later on. So I'll have a think about that. I can maybe add an audio layer for that purpose; I'm quite interested in that, as I've never programmed with sound before