Videos in iTunes lag

I have a problem playing videos in iTunes. The videos will not play quite right. It lags through the movie.
I have updated both iTunes and Quicktime.
I’ve tried to wait 10 minutes between a pause and I have tried to change the settings to play with standard definition.
The same video file can be run without problems in vlc.
I use iTunes on Windows 7 with 6 gb of RAM. When I sync these videos to my iphone, they work perfectly.
I have no problems with other video players, than my iTunes / Quicktime.
I have searched on the web but can not really find anything.
Some say that it’s something with a codec problem, but do not know what to do about it.
But if anyone has a tip for me, then you would be very helpful.
sincerely RichardPoyner
Answer #1
Please Help