Comcast on Tuesday announced the beta launch of Watchable, an app for professional short-form content, as it makes a play for a piece of digital advertising.

The service — an app and a stand-alone website, plus a tab on Comcast's X1 set-top box — will launch with about 30 online network partners, including Buzzfeed, Vox, Vice, Machinima, GoPro and Maker Studios.