I had the same question and Xfinity could not give me an answer. Go to these sites and read the information.
http://forums.comcast.com/t5/Xfinity-Connect-Mobile-App/DVR-Service-Unavailable/td-p/2049769
http://customer.comcast.com/help-and-support/cable-tv/requirements-for-dvr-manager.
Vince