The film mogul Darryl F. Zanuck was among the skeptics in the years before networks started broadcasting shows seven nights a week. “Television won’t be able to hold on to any market it captures after the first six months,” he infamously predicted. “People will soon get tired of staring at a plywood box every night.”

To make sure that television sets would become something more than ungainly appliances, entertainment executives of the late 1940s and early 1950s went in search of programming. And they found it within earshot, in radio shows like “The Lone Ranger,” “Our Miss Brooks” and “Dragnet,” which were among the first TV hits.

With the rise of streaming, the entertainment industry is going through a similar transformation. Executives at Netflix, Amazon and Apple are spending wildly for content, which has created a sense of urgency among their rivals at broadcast networks and cable channels. And like their midcentury predecessors, they have been aggressive about buying up ready-made programming to fill their expanding slates. These days, that means podcasts.

“Homecoming,” the Amazon series starring Julia Roberts, is based on a fictional podcast from Gimlet Media. Bravo’s “Dirty John,” with Eric Bana in the role of the con man John Meehan, is based on a true crime series from The Los Angeles Times and the podcast network Wondery.