Comcast is introducing a service that lets customers make Skype video calls over their televisions, part of a push to add revenue and stem subscriber defections.

The Skype on Xfinity service, which lets users make high-definition video calls, has launched in Boston and Seattle and will be available in cities including Atlanta, Chicago and Miami by the end of the week, the cable giant said.

Comcast is seeking ways to keep its cable customers loyal while adding features that can bring in additional revenue.

Skype on Xfinity, which includes a video camera and a special remote control, lets users make video calls and send instant messages while watching TV.