Until now, most online ad spending has been diverted from brands' print budgets -- but the rise of online video is now letting online marketers make a play for brands' TV budgets too, says RBC Capital Markets analyst Mark Mahaney. "The number of people watching TV seems to be stagnating or declining, and the number of people turning to the Internet for entertainment is surging," he says. "It almost inevitably drives these TV budgets online."