Nearly two dozen TV networks are joining Comcast’s nationwide trial of its On Demand Online streaming video service, thanks to a series of recent agreements. CBS is the latest network to join the impressive lineup, which also includes HBO and Cinemax as of yesterday, and will be offering some of its content through Comcast.net and Fancast.com at no cost for Comcast cable subscribers – at least during the test phase.

Others joining the trial include BBC America, Food Network, A&E, AMC, History, E! Entertainment, and DIY Network. The service comes at a time when consumers are catching on to the amount of content available online, legally or otherwise, and as more cable customers drop their subscriptions. At issue is whether the future of online television will be advertisement-funded or require paid a subscription. Naturally, Comcast aims to preserve the industry’s lucrative subscription business model amid the rise of sites like Hulu and YouTube.

Time Warner is jointly developing the delivery system with Comcast, though its version is called TV Everywhere. Comcast's trial will involve some 5,000 customers throughout the country, with the goal of testing authentication technology intended to keep out everyone but paying subscribers.