Apple is planning to introduce a new Apple TV set-top box as early as April and is negotiating with Time Warner Cable Inc. and other potential partners to add video content, according to people with knowledge of the matter. Apple is aiming to have the device available for sale by the Christmas holidays, though the release date could change because the company is still in the process of securing new agreements with programming and distribution partners, said two people, who asked not to be identified because the plans are private. The new device, which plugs into a television set, will have a faster processor than the previous version and an upgraded interface to make it easier for customers to navigate between TV shows, movies and other online content, one person said. An agreement with Time Warner Cable would mark the first such deal with a pay-TV provider.