[Spoffo]

Suddenly, Quicktime on one of my desktop Macs shows a blank white screen when I try to play back MPEG 4 files though the sound is playing back ok. On my MacBook Pro, which has the identical software configuration, MPEG 4s still play back fine. Also, all the other CODECs I've checked still play back OK on the desktop machine

Details of the two machines:

Desktop (problem) Dual G5 tower, OSX 10.4.11, QT(pro) 7.5.0

MacBook Pro (no problem) 2.16ghz Intel Core 2 Duo, OSX 10.4.11, QT(pro) 7.5.0

It's possible that the problem occurred after a software update, but I don't recall one.

The very specific behavior says to me that somehow the MPEG 4 component of QT got corrupted on the desktop machine. However, my attempt to swap-in the good MPEG 4 component from the laptop was blocked because the suspect file is reported as "in use" all the time and won't let itself be over-written.

I also tried a clean download and re-install of QT (though I didn't manually dump all the QT files first.) The re-install seemed to go fine, but nothing changed.

I'm out of ideas. Anyone?

[Spoffo]

Well, I fixed it, but it certainly was a pain. After plowing around a bunch of Apple support forums and trying every sort of strip-and-reinstall option, the only remaining fix was a complete archive and re-install of OSX 10.4 from my original disc, followed by about an hour's worth of system update to get to 10.4.11 followed by downloading and installing Quicktime 10.4.5

Nobody had any idea what exactly had broken in my QT or why. Just a general conclusion that it was deep in the system level, where once it breaks it stays broken. And one more vote for the idea that QT 7.5 is definitely not ready for prime time! (Even though - so far - it hasn't given me any problems on my Mac Book Pro)