720p video from YouTube. Yes, YouTube. Click to enlarge.

Update: My bookmarklet has been broken by Google, but the script it was based on has been fixed and has added support for 720p HD downloading. Use that instead.

In addition to expanding their player to 960px wide for all videos, YouTube received a more quiet upgrade today. In addition to normal quality and high quality, they have now added 720p HD video. Few HD YouTube videos exist at the moment, but for those that do you can simply append &fmt=22 to the end of the URL. Interestingly, I seem to be the first to have figured out how to actually download (rather than stream) these new 720p HD videos directly from YouTube.

Simply drag this link to your bookmarks bar:  DL YouTube HD

This is what is known as a bookmarklet, a JavaScript bookmark able to act on the current page. To use it, find a YouTube video that’s available in 720p (example). Click on the bookmarklet, and at the bottom of the gray info box on the right a link labled “Download as 720p HD MP4″ will appear. Right-click and save, and the download will begin.

Credits: My bookmarklet is a modification of googlesystem.blogspot.com’s bookmarklet for downloading high quality (but not HD) YouTube videos, which I found via robotdestroy on MacOSXHints.

Update: After seeing my bookmarklet, Nathan Hammond took it even further by making his own bookmarklet that automatically starts the download. Very nice!