ALITTLEDESIGN  I am experiencing exactly the same thing with the Finder after updating Quicktime 7.6. Finder window blinks and no matter the application window I will be reverted to the Finder and have to "click" back into the application. Have tried the link suggested for stuffit system preferences and so far, so good.

http://www.macfixit.com/article.php?story=20090121223437550  
(Version 7.6)

MCRAIGCHR  I'm having the same problem. 10.4.11 ... Finder crashing constantly.  
(Version 7.6)

YOUDAMNKIDS  Woops, didn't see that you could reply to other comments, but yeah, I'm having the same problem in 10.4.11, and it did auto update.  
(Version 7.6)

YOUDAMNKIDS  I don't think it's a sytem version issue, because I just installed the Tiger version linked at the top of the page, and I'm still having the same problem.  
(Version 7.6)

YOUDAMNKIDS  Two things:

!) I've noticed it's not just changing the system's focus, it's actually restarting the finder every couple minutes. Icons blink, system focus changes, and any open finder windows close.

2) Reverting back to an older version of Quicktime doesn't stop this from happening.  
(Version 7.6)

YOUDAMNKIDS  Here's a fix for anyone still needing it:

http://www.macfixit.com/article.php?story=20090121223437550  
(Version 7.6)

MISHA  Might be an issue with the test video, then. VLC is more forgiving of encoding errors than QuickTime is, but that doesn't make it any 'better'. What codec does the video use? When was it encoded, and using what?  
(Version 7.6)

GREGM  MISHA

Created June 2004

Apple Cinepak

320 x 240,

Millions

8-bit Unsigned Integer, Mono, 22.050 kHz

Dumped Perian, thinking that might be a conflict --- QT 7.6 still pixelated, 7.5.5 OK  
(Version 7.6)

MISHA  Wow, Cinepak... haven't heard that name in years. That's an ancient codec, great for its time in the '030/'040 and 386/486 days but pretty ancient by today's standards and seldom used. Not saying that's a reason why it *shouldn't* playback in QuickTime anymore, just that that probably shouldn't be your benchmark for whether QuickTime playback is performing up to expectations.

For that, I'd check out something newer... like a video encoded with h.264 at an HD resolution, such as one of these: http://www.apple.com/trailers/disney/earth/hd/

If you're still using Cinepak, I'd be curious to know why... unless you need compatibility with really old hardware, h.264 is the way to go. The baseline profile is relatively lightweight (which is why even 5G iPods can play back video encoded with it).  
(Version 7.6)

GREGM  Thanks Misha

I was able to convert to a nice h.264 with a multitude of programs in the pre-update system.

After updating to 7.6, the only thing I had that would do it *without* "preserving" the pixelations was my old VisualHub.

As for why I keep it --- I had a close relative that disconnected from the world for a while. His response to my worries was the short cute "Happy Boy" clip.  
(Version 7.6)

ROBBY.IS.ON  ...and three stars for that! Right... oO  
(Version 7.6)

ECHOROB  Sorry forgot to say i am running 10.4.11  
(Version 7.5.5)