Viacom President and CEO Bob Bakish and Les Moonves, CBS Chairman and CEO of CBS.

CBS and Viacom CEOs met Friday to discuss a deal to combine the two companies, sources told CNBC.

Les Moonves of CBS and Bob Bakish from Viacom are talking as the companies have made their requests for due diligence materials, the sources said. But the special committees of their boards have yet to meet.

Earlier this month, the boards of both companies said they had formed the special committees to explore a combination. Both companies, which are primarily owned by Sumner and Shari Redstone and split apart a decade ago, face a rapidly changing media industry. A deal could combine CBS's broadcast network with Viacom's cable channels and film studios.

Shares of CBS and Viacom were flat Wednesday.