HD Lag?

Well ok so iv been trying to watch this clip on YT but when I go to play it in HD mode it gets uber laggy and just doesnt play at all, now I would assume the problem lies with my internet, but no, I have downloaded the video and when I play it on WMP I still get the super lag? iv run scans on my computer and iv definatly got no infection so why isnt it showing it in HD?

the clip I am trying to watch is this: YouTube - templar aion

Well, it works just fine for me. It's something on your end. What it is though, I have no idea. Sorry.