Comcast adds 18 networks to online trial

CBS is first broadcast network to join

CBS and 17 cable networks are joining the Comcast online video trial called Online on Demand.

The news comes one day after HBO and Cinemax joined; TBS, TNT and Starz came on board earlier.

Comcast in a few weeks will test the service, which gives cable TV subscribers access to shows online without an extra fee. Comcast wants to rebrand the service and take it nationwide by year's end.

Comcast -- and the cable networks involved -- are hoping they have found a way to retain subscribers even as more and TV shows make their way to the Internet at sites like, which is owned by Fox, ABC and NBC.

Also joining Online on Demand on Tuesday were AMC, A&E, BBC America, DIY Network, E! Entertainment, Fine Living Network, Food Network, HGTV, Hallmark Channel, History, IFC, MGM Impact, Sundance Channel, WE tv, the Style Network, G4 and Fearnet.

CBS is the first broadcast network on board. Much of its programming is available online at its own