Fox Corp. and Comcast Corp. are each in discussions to acquire advertising-supported video services, as entertainment giants increasingly look to offer free or low-cost alternatives for consumers who don’t want to pay for streaming subscriptions.

Fox has expressed interest in acquiring Tubi, an ad-supported streaming service that carries reruns of television shows and movies, according to people familiar with the matter. The companies are discussing a deal that could be valued at north of $500 million, the people said.

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