Comcast is launching yet another video streaming service for you to consider purchasing.

The cable giant announced today it's launching Xfinity Instant TV, what is essentially a bundle of local broadcast networks, for $18 per month. The service will only be available to Comcast broadband subscribers.

The company said the new service is currently available in select areas and will be rolled out nationally in markets where Comcast is offered over the next two weeks.

This type of "over-the-top" offering is far from new. Comcast will be pitting itself against other services such as Sling TV, YouTube TV, and Hulu Live TV that also offer live television over the internet rather than a traditional cable subscription.

What's still unclear is the benefit this service would have over a simple TV antenna. Right now, most people can already get access to local standard cable channels using an HDTV antenna, which costs about $30. Based on what Comcast is saying, it appears there will be quite a lot of overlap.

"Available channels vary by region, but all Limited Basic lineups include popular broadcast channels like ABC, CBS, The CW, FOX, NBC, and PBS as well as public, educational, and government channels. Plus, most include Univision and Telemundo," Comcast says on a Xfinity Instant TV support page.

One of the major selling points of this new service is that subscribers will not need a set-top box (like they do with a traditional cable subscription), and they can also add or remove programming bundles at any time.

The goal here appears to be upselling customers who are subscribing to broadband but not cable TV. This new streaming service could entice some of these customers to upgrade and essentially serve as an on ramp to full-fledged cable subscriptions.

The only major drawback here is that the basic Xfinity Instant TV package doesn't come with popular cable channels like ESPN, CNN, MSNBC, or CNBC (ones that can't be accessed using a simple TV antenna). Those channels will cost customers an additional $30 per month.

Comcast is also offering an entertainment package that includes cable channels like A&E, AMC, Comedy Central, Discovery, Food Network TBS, TNT, and USA for an additional $15 per month. A kids and family option is also available for an extra $10 a month and includes channels like Cartoon Network, Disney Channel, MTV, and Nickelodeon.

Xfinity Instant TV will be available on most popular platforms including web browsers, mobile apps, and streaming devices such as Roku. Another weird detail: the subscription won't let customers rent or purchase videos on-demand. Customers also won't be able to buy pay-per-views with the service (sorry, UFC and boxing fans!).

Whether the new service actually catches on remains to be seen. Comcast has already been testing the service in Boston and Chicago for the last two years with at least some success. Now that it's being rolled out nationwide, the real test begins.