Comcast has had a rough couple of weeks with the implosion of the Time Warner merger. Maybe releasing a new feature will help it move past the disappointment? Xfinity Share is a tool that lets you stream pictures and video to a cable box, either yours or someone else's. This is part of the Xfinity X1 platform, so both you and the owner of the target box need to be subscribers.
Xfinity Share uses WebRTC to stream content from your phone to Comcast's set-top boxes. Your Xfinity contacts will be prompted to accept streaming invitations on their TV when you send a feed—so no, you can't just take over their screen, as fun as that would be. You can send live video or still images. You can also stream to other mobile devices using the Xfinity Share app.
There are obviously plenty of ways to share live video streams, but they usually require you to use a computer or phone to view them. This works on a TV, which makes it better for family members of a more... advanced age who might not be good with computers. In the coming months Comcast will add URL sharing, up to five simultaneous viewers, playback control for viewers, and photo storage in the X1 photos app.