Thanks so much for the answer Alan. But everything is updated to the latest.
I have:
reinstalled windows 8 and done all the updates
installed all the latest intel drivers (except chipset and infrared that for some reason wont install)
installed the latest silverlight and the latest flash player.
tested youtube and netflix on both firefox, ie and chrome.
tested netlix on the netflix app.
All this is tested on a panasonic viera p55st50 (plasma tv) running on 50hz
conclusion.
besides the weird driver problem all youtube and netflix videos are stuttering.
I have attached my dxdiag outputfile.
regards
Daniel