Comcast yesterday launched an online streaming video service for its Internet customers; the $15-per-month "Comcast Stream" will include live TV from HBO and broadcast networks as well as on-demand videos.

In a first for Comcast, the package will not require a cable TV subscription. But it still has a major limitation. Live TV channels can only be watched while customers are on their home Internet connections. When customers are on the road, they'll be able to watch on-demand and recorded videos but not live TV through Comcast's service.

Comcast Stream may end up providing a good amount of out-of-home video, though. Like a cable TV account, a Comcast Stream subscription will still let users sign into channel-specific apps such as HBO Go from any Internet connection.

Comcast also promised Stream customers access to its existing cloud-based DVR service that lets you "record all your favorites and watch them later." The cloud DVR stores recorded TV on Comcast servers and lets customers access it anywhere, but the recordings are managed by the home Internet gateway. This limits customers to recording two channels at once and storing 20 hours of video.

Besides HBO, supported networks will include ABC, CBS, CW, FOX, NBC, PBS, Telemundo, and Univision. Local channels will vary by market.

Comcast describes the new service as "streaming cable." This apparently isn't just semantics—a Comcast spokesperson told Ars that Comcast Stream is delivered as a managed service over the Comcast IP gateway in customers' homes. This should ensure a quality of service similar to what's provided by cable TV. But it won't be on your TV, because Comcast Stream works on phones, tablets, and computers, but doesn't have an application for set-top boxes like the Apple TV or Roku.

You could hook a laptop up to your TV or sign into channel-specific apps on any number of set-top boxes, but that's not as convenient as it could be. Comcast has also controversially taken its time striking deals to authenticate applications on third-party devices such as the PS4.

Comcast Stream is "unlike anything we’ve ever offered: no extra device or additional equipment required… or even a TV," the company said in its announcement. "With Stream, Xfinity Internet customers can watch live TV from about a dozen networks—including all the major broadcast nets and HBO—on laptops, tablets and phones in their home. It includes thousands of on demand movies and shows to watch home or away and even comes with access to TV Everywhere and a cloud DVR so you can record all your favorites and watch them later."

Comcast’s previous streaming efforts were unpopular

A previous Comcast service called "Streampix" launched in 2012 but required a cable TV subscription—except in one trial area where it was available to a small number of broadband-only customers.

Comcast's previous streaming video attempts have been failures by the company's own admission. Comcast's streaming ambitions became a key topic when the company attempted to purchase Time Warner Cable; that deal was thwarted by regulators who said they worried a bigger Comcast would use its control of customers' Internet connections to squash competition from online video services that market to Comcast broadband subscribers. Comcast had tried to convince the government that it would pose no threat to online video companies because its own streaming products were unpopular.

The new service will be available to any Comcast Internet user. That's more than 22 million subscribers, giving the country's largest ISP a new way to compete against Netflix and other online video companies in its own territory. Comcast has revealed no plans to offer the service to users of other Internet access providers.

"Stream will be available to our Xfinity Internet customers for only $15 per month and will first launch in Boston at the end of the summer," Comcast wrote. "We’ll take it to Chicago and Seattle next, with plans to make it available everywhere in our footprint by early 2016. To find out when Stream is available in your area just email us here."

Comcast Stream is cheaper than Dish's Sling TV, which also offers live TV channels, but Sling TV doesn't require a subscription to any specific cable or satellite provider and works anywhere in the US. The basic Sling service is $20 per month and comes with channels such as ESPN and AMC, which aren't available on Comcast Stream. But Sling TV charges $15 per month extra for HBO.

If purchased separately, HBO's online service HBO Now costs $15 per month, but it works on any Internet connection. TV viewers can also get broadcast networks for free after buying an over-the-air antenna.

Channel offerings for Comcast Stream could expand, but for now the service doesn't offer ESPN or regional sports networks, so customers with extensive sports watching habits will still want to buy a much pricier cable TV subscription.

Comcast customers will be able to sign up for the new service without calling the company, and they can also cancel online. That can only be viewed as a positive, given how difficult it can be to sign up for other Comcast services and how difficult it can be to cancel them. Comcast Stream has no long-term commitments or contracts.