"Today at the VidCon 2010 conference, we announced support for videos shot in 4K (a reference resolution of 4096 x 3072), meaning that now we support original video resolution from 360p all the way up to 4096p. To give some perspective on the size of 4K, the ideal screen size for a 4K video is 25 feet; IMAX movies are projected through two 2k resolution projectors.
We always want videos on YouTube to be available in the highest quality possible, as creators intend. In December of last year, we announced support for 1080p, or full HD. At 1096 x 3072 pixels, 4K is nearly four times the size of 1080p. To view any video in a source resolution greater than 1080p, select "Original" in the video quality pulldown menu:
To illustrate the power of 4K, please check out the videos in this playlist; each one was created by a filmmaker with access to a 4K
camera. (Be warned: watching videos in 4K, even on YouTube, will require
ultra-fast high-speed broadband connections).
Because 4K represents the highest quality of video available, there are a few limitations that you should be aware of. First off, video cameras that shoot in 4K aren’t cheap, and projectors that show videos in 4K are typically the size of a small refrigerator. And, as we mentioned, watching these videos on YouTube will require super-fast broadband."