thanks for the info. I was aware that Mplayer OSX does launch a 
seperate tool, but not that MythTV directly launches these playback 
tools by itself.

That, of course, would explain it.

I've just had a look at the subapp bundles and their structure is 
quite f***ed up (sorry) - especially with regards to their missing 
bundle identifier. Another problem is that I have no idea on whether 
these seperate tools will react to key presses at all or under which 
circumstances which one is invoked (there seem to be at least 4 
different versions).

Best regards, 
Felix