Xbox One's built-in game footage buffer is limited to recording at 720p/30fps resolution, regardless of how high-res the actual game you're actually playing may be.
The limitation's obviously been put in place to stop the constant buffering system from eating up too many resources and absorbing all your hard drive space, as even capturing five minutes worth of 1080p video would result in an enormous video file that'd be a pain to store, edit and share online.
It does mean there will be a small drop in quality, though. Xbox One games are targeting the full 1080p at 60fps HD dream, so your magic headshot moments won't be saved at quite the same level of clarity. Your grandchildren won't be quite so impressed when browsing your YouTube channel 50 years from now. [IGN via Eurogamer]