IN THIS ERA of cord-cutting and streaming services, there has remained one constant for television networks and advertisers looking to draw a crowd: live events.

Millions of Americans have continued to flock to their TVs during prime-time hours to catch extravaganzas like the Olympic Games, the Super Bowl or the Academy Awards as they happen. But even live events are now finding their way onto streaming platforms, and marketers are wondering how they can be sure to reach those viewers, too.

“What you’re seeing is a shift in how people engage with content that they still care passionately about,” said Simon Wardle, chief strategy officer of Octagon, the sports marketing unit of the Interpublic Group. “It’s indicative of this world of choice in which consumers live, which is fantastic if you’re a fan but is a little challenging if you are an advertiser or a brand trying to engage those fans.”

The change came into stark relief this month during the Summer Olympics in Rio de Janeiro. Thirteen days in, NBC’s average prime-time audience of 26.7 million viewers was incredibly high — more than triple the combined number of people watching ABC, CBS and Fox at that time. But it fell short of the network’s hopes. Some of that slip could be attributed to viewers dispersing to NBC’s live streams online or to its cable channels like MSNBC and Bravo, which were also showing the Olympics. (Also surely a factor: Some marquee events were shown on tape delay in prime time, meaning many fans already knew the outcome and may have been less inclined to watch.)