AT&T did not disclose the terms of the deal.
Chernin Group, former News Corp president Peter Chernin's holding company, produces films and TV shows, and has a stake in Crunchyroll, a subscription and video-on-demand service.
"AT&T's massive reach on those platforms across mobile and broadband and their commitment to the online video space make them the perfect fit for this venture with us," Chernin said.
Earlier this year, The Chernin Group tried to buy the Hulu online video site.
In January, Verizon acquired Intel's OnCue service for an undisclosed sum to accelerate its push into next-generation video services.