The deal that should get done in the media world is a merger of Time Warner and CBS, former CBS CEO Mel Karmazin told CNBC on Tuesday.  In fact, he said, he would even invest his own money if such a deal were to materialize.  "It just makes sense. What's the reason it wouldn't work?" he said in a "Squawk Box" interview.  He said such a combination would have synergy: Time Warner has Warner Bros. Pictures, while CBS has no movie studio. The companies could also fit well together in sports and news. Timer Warner operates Turner Sports and CNN. Leveraging CBS' deal to carry NFL games could also help a combined company in negotiations with cable providers, he added.  Read MoreNo 'significant' talks to buy AOL: Verizon CEO  Media companies have no choice but to expand in today's business, he said.  "If you take a look and you see all the consolidation that's gone on in the advertising agency world, you see that there is so much advertising inventory out there that there is far more supply than demand," he said. "In order to have the position to deal with advertisers, to deal with distributors, you need to be bigger."  Two major deals—Comcast Cable's bid to buy Time Warner Cable and AT&T's offer to purchase DirecTV—will likely be approved, said Karmazin, who also held executive positions at Sirius and Viacom..  "It should get done. It's hard to find good reasons to stop it, and I believe at the end of the day it's not anticompetitive. I don't believe that there is any monopoly they're going to have. I don't think it's going to be harmful and I think that the competition doesn't like it," he said.  Read More Streaming has put 'fear in the eyes' of old media: Levinsohn  On the issue of "unbundling" television content—or offering it outside of traditional cable packages—Karmazin said it offers consumers greater choice, but the vast majority of people will still want the whole slate that cable subscriptions provide.  "I don't believe this 'quote' little bundle is going to get a whole lot of people to not have the broadcast networks, to not have CNBC, to not have all of the great content out there," he said, referring to Dish Network's decision to unbundle certain channels, including ESPN.  Read MoreDish's Sling TV launches $20, live, over-the-top service
Former CBS chief Mel Karmazin also says media companies must get bigger in order to deal with advertisers and distributors.