It seems that in addition to the 5 minutes of continuous recording, the Xbox One will record the moment when you unlock and achievement. Moreover, Microsoft opened the possibility to devs of also recording player’s reaction with Kinect when this occurs.
All this info was from Xbox Australia product manager Adam Pollington in an interview with YouTuber ChampChong at EB Games Expo.
Official Source: http://www.youtube.com/watch?feature=player_embedded&v=D9CNbpFdQvw
http://gearnuke.com/xbox-one-dvr-records-gameplay-every-time-an-achievement-is-unlocked/