That's right, Xbox One has the capability to capture HD videos, but you'll only be able to share them on XBL at launch - Facebook and Youtube to follow in 2014 according to to Microsoft’s Albert Penello.
During a recent demonstration of the Xbox One's interface, Penello is reported to have stated that captured videos will not be shareable beyond Xbox Live - he hopes to see Facebook at Youtube following in 2014.
According to Destructoid
, a 30 second gameplay clip was saved in 720p almost instantly using a simple voice-activated command over Kinect.
Sony's PS4 will support HDMI video capture too, but not at launch - read here.