The signals only work for TV subscribers who are also Time Warner Cable Internet customers and are on their home Wi-Fi network. They must live in an area that runs from Ventura on the coast to San Bernardino inland and south through San Diego.
The addition of the local ABC, CBS, NBC and Fox affiliates, among about 50 other stations, rounds out a lineup of more than 100 live TV channels that can be watched on smartphones, computers, tablets, Roku streaming devices, Samsung smart TVs or Xbox 360 consoles.
The move is part of a four-year-old industry initiative called "TV Everywhere," which is meant to enhance the benefits of a pay TV subscription and dissuade customers from dropping service in favour of video streaming services like Netflix and free TV that can be accessed with an antenna.
The company has said that it wants to enable viewing of its TV programming on whatever devices its customers choose, partly on the hope that it can one day save costs on maintaining its fleet of set-top boxes.
Time Warner Cable, the nation's second-largest cable TV provider, launched live local TV station signals on its app in New York in March 2012 and in Kansas City in April.
The major cable and satellite TV companies offer a wide range of content through apps, but it's mainly on-demand reruns so subscribers to catch up on episodes of shows like "The Walking Dead."
TV providers and network operators have been slow to offer the same access to live TV programming, mainly because mobile viewing has not been counted in audience ratings by The Nielsen Co. The ratings agency plans to launch mobile measurement next fall.
"The big hang-up for the networks is measurement," said Bill Niemeyer, a senior analyst with research firm The Diffusion Group. "They get paid based on who's watching, and if somebody's watching the live linear broadcast on a device that isn't getting measured, it's like it's not happening and they're not getting paid."
Consumer demand for live TV programming over the Internet is strong, the research firm found. In a survey it conducted in January, the company found that nearly half of the 1,000 U.S. adult broadband Internet users it polled had watched live programming over the Internet through such services as Watch ESPN.
More than a third of respondents said their view of their TV operator would improve if they were offered live TV access on all their devices.
The Walt Disney Co. began making live local ABC programming available on its Watch ABC app in May and has now rolled out the service to subscribers of certain pay TV providers in the eight markets where it owns stations, including New York, Los Angeles and Chicago.
The Watch ABC app is truly mobile, allowing customers to view live broadcasts outside their homes and on cellular data networks. The app inserts ads that are sold separately from the Nielsen-rated system for mobile viewers.
Despite the lack of mobile viewing measurement, NBC also plans to make its live local TV stations available through apps beginning in major markets early in the new year, according to Ron Lamprecht, executive vice-president of digital distribution at NBCUniversal, a division of Comcast Corp.
Viewing will be available both in and outside the home and the company will sell advertising separate from the Nielsen system for now, he said.
"There's enough value here for us and consumers to get going on this," he said. "We'll develop the advertising piece as we progress the product."
Not all the major broadcasters are moving quickly to enable live local TV programming over the Internet.
CBS Corp. invested in a digital video delivery company called Syncbak in April but has yet to unveil its plans. Fox, a unit of Twenty-First Century Fox Inc., is backing a mobile offering called Dyle Mobile for on-the-go viewing but it requires a mobile antenna attachment that is sold separately.