You're asking for site-related tech support. So, as far as I know, this [u]is[/u] the most appropriate place to post your question.

I'm using the site from a Windows computer and I've never had that problem. It does sound like something you may be able to fix by updating your graphics card video drivers.

You can also try using the forum's search feature to locate past threads that deal with video playback issues.

Nicolai