Hulu, the NBC Universal/Fox Internet joint venture, currently in its beta stage and available to only a select group of testers, has begun adding high-definition content in the form of movie trailers and clips, it said Tuesday. Universal Studios has provided five of the 10 clips; 20th Century Fox, the other five. Unlike other content on Hulu, the HD clips do not include additional advertising. Testers reported that the HD video represented a significant improvement over Hulu's usual quality but that it takes longer to load and sometimes "skips."