With streaming ads poised for rapid expansion, the move will hasten advertisers’ exodus away from cable almost altogether.

Comcast is moving forward the spinoff of its cable network channels, a source familiar with the matter told CNBC's Julia Boorstin on Tuesday. The separation is expected to take about a year, and an announcement from the company could come as early as Wednesday,

Bravo stays with NBC, but other longtime cable networks such as E!, USA and MSNBC will be part of a new company.