YouTube recently launched an exclusive High Definition section for the US users. Users who have access to this section can watch the videos in 720p HD quality.
How YouTube has this working is when you happen to upload a video onto YouTube in HD quality - YouTube will automatically have a new buton called "Watch it in HD" just below the player's lower right hand corner. Currently you have a button called "watch it in high quality" in that space for a few videos. On clicking the "Watch it in HD" button, it expands the standard viewing window to 16 x 9 with a 1280 x 720 resolution for HD viewing.
Also, YouTube already says that users who would like to have their videos available in HD quality need to look at the videos' aspect ratio. Also, the new YouTube widescreen player will automatically add "pillarbox" bars to 4:3 videos, so if a video was already letterboxed to fit the 4:3 window, it will be doubly resized (that's a concern since it will surely create an unpleasant viewing experience).
Currently we are seeing that the HD resolution of 720p is fast becoming a standard among the online video sharing sites. Professional video content syndication web sites such as Hulu already offer HD as an option. Soon we'll have Netflix and Amazon video on-demand services to offer high definition through the browser as well. So this area is gonna be competitive!!
