After upgrading to iTunes 7, playback of videos purchased from the iTunes store became unwatchably slow and jerky. The video would play for about 1 second, then freeze, then play, then freeze.
The solution was to turn off the Internal microphone in sound control panel under "Input".
Thanks to Wmatthies on the Apple discussion forums for this idea.
I had the same problem with iTunes v7.5.
I resolved it by getting into Quicktime Preferences, Advanced, and unselected all check boxes under DirectX section, those related to video acceleration.
Now it works perfect!
Posted by: Sergio on November 14, 2007 7:50 AMHad the same problem when upgraded to 7.5 - the DirectX solution worked great!
Thx
Posted by: B_Sharples on January 2, 2008 3:11 PMSanity restored. Many thanks.
Posted by: rtm on March 13, 2008 6:52 PM