Argh. What a strange thing. Took me a while to figure this out. It quartz extreme is graphics acceleration For Mac os x.
If you boot up a mac mini and the display is off it assumes it is a headless Mac and turns f quartz extreme acceleration.
but then if you try to watch tv and the tv is turned in later you don’t get any graphics acceleration and everything from vlc to iMovie fails.
So you either need to remember to leave you ac system powered up when you reboot. Or you have to buy a gizmo that fakes out the hdmi signal. Argh!