On the roof of a luxury building at the edge of Central Park, 585 feet above the concrete, a lawyer named David Goodfriend has attached a modest four-foot antenna that is a threat to the entire TV-industrial complex.

The device is there to soak up TV signals coursing through the air — content from NBC, ABC, Fox, PBS and CBS, including megahits like “This Is Us” and this Sunday’s broadcast of Super Bowl LIII. Once plucked from the ether, the content is piped through the internet and assembled into an app called Locast. It’s a streaming service, and it makes all of this network programming available to subscribers in ways that are more convenient than relying on a home antenna : It’s viewable on almost any device, at any time, in pristine quality that doesn’t cut in and out . It’s also completely free.

If this sounds familiar, you might be thinking of Aereo, the Barry Diller-backed start-up that in 2012 threatened to upend the media industry by capturing over-the-air TV signals and streaming the content to subscribers for a fee — while not paying broadcasters a dime. NBC, CBS, ABC and Fox banded together and sued, eventually convincing the Supreme Court that Aereo had violated copyright law. The clear implication for many: If you mess with the broadcasters, you’ll file for bankruptcy and cost your investors more than $100 million.

Mr. Goodfriend took a different lesson. A former media executive with stints at the Federal Communications Commission and in the Clinton administration, he wondered if an Aereo-like offering that was structured as a noncommercial entity would remain within the law. Last January, he started Locast in New York. The service now has about 60,000 users in Houston, Chicago, Boston, Philadelphia, Dallas and Denver as well as New York, and will soon add more in Washington, D.C.