Essentially, the app turns your Xbox 360 game system into an additional receiver for Xfinity video content that's streamed over the High Speed Internet portion of your Comcast "double play" service. To make it all work, you have to subscribe to both Comcast's Xfinity TV and High Speed Internet, as well as Microsoft's Xbox Live Gold which costs $99 a year.
No live (or "linear," in cable-speak) TV shows will be available through the app, at least at launch. But there will be "thousands of TV shows and movies" to chose from - many free, some for rental.
And here's the most interesting (and controversial) revelation in the posting. Because the content is being delivered over Comcast's "private IP network and not the public internet," the cable-co won't "count" the streaming "against a customer's bandwidth cap" as it now does with users of other streaming services. (Go over the cap and the operator can shut off or slow down your service, until the beginning of the next billing cycle.)
Why are customers of Comcast digital TV shut out, if they use another provider for internet? According to the FAQ, the streaming service needs "a Comcast modem to verify that the customer is in the home and to deliver the content to the Xbox." Bummer.
Adding extra gloss - Xfinity TV for Xbox works with the game system's Dashboard search tools and with the voice/gesture navigation of the Kinect peripheral.
Update: Just received a statement this afternoon from the Washington, D.C. based communications watchdog group Public Knowledge, suggesting that Comcast's favored nation treatment for streaming Xfinity TV runs counter to the principals of "net neutrality." . Here it is: