The "Misc Options" gives you the option to choose, if audio shall be recorded or not, by selecting "Captur Audio". Of course, this is only possible, if an audio source is available.
Beside that, you have the option to cancel the audio recording after a set time automatically. "Use Timelimit" is the selector and enter the time in seconds.
1 minute = 60 second
1 hour = 3600 seconds
If your graphic card, does not support Overlay, or if you are having troubles
with this, deactivate it, by using the "Overlay"-Switch. This might
lower your capture speed.
Newer Graphic Boards should support Overlay without any problems.