Verizon and Hearst are building a joint venture to make digital video aimed at young viewers known as millennials, aiming to launch two channels in the spring on platforms like the mobile carrier's Go90 app and its unit AOL. The two channels, RatedRed.com and Seriously.TV, will launch before NewFronts, a series of New York-based events during which digital media companies fete advertisers and media buyers with the hope of scoring ad deals.