NEW YORK (AP) — Comcast, the country's largest cable company, is offering its own online video alternative as people spend fewer hours watching live TV and more time using tablets and phones for entertainment.

The new service, called Stream, will be available to Comcast's Internet customers and cost $15 a month. For now, it will include only broadcast networks like FOX and NBC in addition to HBO, but no cable channels like AMC or TNT.

Anyone can watch broadcast networks for free on a TV with an antenna, which costs about $20 and up. And HBO already sells a stand-alone streaming service for $15 a month.

Comcast has ambitions to offer more TV online, however. It wants to add cable channels over the next year so that online TV subscribers have "access to any of the content we have available" for traditional cable customers by the end of March in 2016, said Marcien Jenckes, Comcast Cable's executive vice president for consumer services. Prices will be similar to traditional cable, he said.

Comcast's service, which is only for its customers, follows the launch earlier this year of Dish Network's nationwide Internet TV service, Sling TV, which sells for $20 a month and includes cable channels like ESPN, AMC and Food Network. You can also add on HBO. A slew of Internet TV options have come in the past year as many cable and TV companies think younger customers prefer to watch TV online, without paying for a full bundle that can easily top $70 a month.

The ability to smother competitors' online TV services was a major reason why regulators were concerned about Comcast's bid to buy Time Warner Cable. It would have created a TV and Internet behemoth that would serve more than half of the country's high-speed Internet customers, as calculated by the government.

The deal never went through. Comcast dropped its bid in April.

Comcast Corp., which is based in Philadelphia, said Monday that it will launch the service in Boston at the end of the summer, followed by Chicago and Seattle. It plans to make it available to all its Internet service customers by early 2016. Jenckes declined to say how many customers Comcast hoped to win online.

Comcast had more than 22 million Internet customers at the end of the first quarter.

The Stream service has limitations. You can watch live TV at home but there are rights restrictions for a lot of live content if you want to watch on your phone outside your home network.

It will work on computers, tablets and phones but won't work directly on TVs. Instead, users can log in to HBO's app and other channel apps through TV-connected gadgets like an Apple TV or Roku, for example.

Stream does come with a DVR service that can store 20 hours of video.

Many young people like sharing passwords for online TV accounts with their friends. Stream allows only two streams on separate devices at the same time.

Like with Dish's Sling TV, Stream customers could sign up online and disconnect the service at any time. A major complaint about cable service is contracts that are difficult to escape and having to drop off set-top boxes and other equipment after canceling service.

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Damian Troise contributed to this report.