Yeah, that works fine too. I cannot reproduce the error on the commandline as any user.

What's weird is the format of the error:

sh: /usr/bin/mplayer: Permission Denied

I only see it in the browser (or the debug.txt file) and it only seems to happen with the thumbnail creation. The conversion itself works.

I swear I've seen this happen before with PHP, but I can't remember. Something is preventing the shell from executing the mplayer binary.