Update: Albert Penello has recently confirmed that the footage is indeed faked. The info comes by way of a thread on NeoGAF:
A new leaked video has surfaced on YouTube that claims to show off the Xbox One’s start-up screen, giving an impression on how long the console might take to boot up.
The footage itself is only nine seconds, but if genuine, it displays the Xbox One’s rather swift start-up sequence and fluid transitions.
The question of the video’s authenticity is still a major factor, and has since been unverified, but there are also other things to take into consideration including the lag in timing that arises from the console’s initial power-up. The video shows a boot time of five to six seconds for the Xbox One, which is a fraction of the time it takes current-gen consoles like the PS3 and Xbox 360 to start-up.
Although the footage basically matches the recent screens of the Xbox One’s UI–except for the black background–it may very well be illegitimate, but even still it will be interesting to see how far the console’s actual boot-up timing strays from the sequence in the video.
Via EGM Now