Two years ago, streaming-device maker Roku circulated a presentation to partners that showed a school of fish swimming toward an area marked “subscription.” Meanwhile, a lone fish labeled “Roku” was heading away from the group toward an area called “advertising.” The implication: Roku was swimming against the tide by launching a free, ad-supported streaming channel for users of its devices.

Now, that presentation would have to look different. Partly drawn by Roku’s early success, the number of fish swimming toward advertising-supported online video is growing: Viacom is in talks to acquire Pluto TV, an ad-supported streaming service, in a deal that could be valued between $300 million and $500 million, according to three people familiar with the matter. The media giant, which owns Nickelodeon, Comedy Central and MTV, had also held talks with Pluto TV competitor Tubi TV.