YouTube High Definition or almost or better then 320x240
www.squidoo.com/youtubehdyou can now view youtube videos in 640x480 or the highest the video was uploaded up to 640x480
this is standard TV size or definition.
there are other websites that offer "real HDTV" video like
Veoh and awesome the best so far is www.vimeo.com/hd supports HD in 1280x7201. On your YouTube Account page,
2. click on Video Playback Quality and you're now able to choose
"always show me higher quality when available" or
"I have a slow connection.
Never play higher-quality video" which is set by default.
So if you want to turn on HD, you must set "I have a fast connection. Always play higher-quality video when it's available" but only if you have a fast internet connection, otherwise you might find that videos don't play as quickly or smoothly.