YouTube has recently doubled its video limit size from 1GB to 2GB, allowing you to upload longer and larger video files. You can also “force” HD viewing of videos by adding &hd=1 to the end of the video URL. See our previous story on accessing “Higher Quality” YouTube videos.
For example, if you upload a video and its URL is http://www.youtube.com/watch?v=pxyJ_ZQVhTI, add &hd=1 to the end to get a larger and higher resolution video playback. Hence, http://www.youtube.com/watch?v=pxyJ_ZQVhTI&hd=1 would be the complete URL.
Here is some more information on uploading HD video directly from the YouTube blog:
“To embed the HD version of a video on a website or blog, click the ‘customize’ button to the right of the embed box on the video page. Some options will appear; simply check ‘play in HD’. The embed code that’s generated will cause the video to start playing in HD as soon as a viewer clicks play. We recommend embedding HD videos at the largest size (853×505) for maximum enjoyment.”