I've been able to do it by resizing the video to 1280x720
Here's an example:
http://www.youtube.com/watch?v=5oh3GKnHBbw (skip ahead a bit; for some reason the beginning of the video is glitched and gets stuck)
The question here is not whether you can do this though... it's whether you'd want to. Unless you have a crap-ton of money chances are that you're going to be capturing at something like 640x480 interlaced. When you blow that up to an HD resolution the result is pretty ugly, as the crap resolution and deinterlacing artifacts become very visible.
Despite this in the past I would have recommended doing this 100%. When youtube first started doing HD their player was still standard size, which meant that HD videos were essentially just higher quality versions of regular HQ. They looked MUCH better. Now that youtube has upped the player size for HD videos (
![Frown :( :(](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
) though it's really up to you. The increased size makes said artifacts more visible, but on the flip side HQ widescreen videos look like crap anyways, so it just depends on your own taste.
(I say they look like crap because with widescreen videos youtube takes the standard HQ 480x360 resolution and reduces the vertical resolution to make it fit in a 16:9 screen; resulting in 480x270. When that reduced res video is streched to fit the new larger widescreen player the result isn't very flattering. Despite that I go widescreen anyways because the extra viewing room is very nice. Just think of youtube adding widescreen as a clever way to reduce bandwidth costs
![Stick Out Tongue :p :p](/styles/default/xenforo/smilies/tongue.gif)
)
oh, and here is the same vid above in standard HQ:
http://www.youtube.com/watch?v=bHrLjLBn0m8.