How can you watch YouTube videos in high definition?

Add this to the end of the video url: &fmt=18

For example...

Normal Quality: YouTube.com/watch?v=LU13MRtSD7E">http://YouTube.com/watch?v=LU13MRtSD7E

High Definition: http://YouTube.com/watch?v=LU13MRtSD7E&fmt=18 Just one step! 1. watch full song on you tube (enabled HD) then go to run type (%temp%) then click UP and open temporary internet files. arrange by size and then copy largest file to your document. or if you are Windows Seven or Vista users then type this C:\Users\yourusername\AppData\Local\Microsoft\Windows\Temporary Internet File