Ancestry web Links on the persons overview page can also be used for storing links to youtube videos. The main advantage is indeed the fullscreen mode. There are still some disadvantages of this workoround: 1. Creating the link for every person separately. Never ever replace the video on youtube or you have to change every reference on ancestry manually. 2. Probably not a solution for private family trees. 3. Youtube can drop accounts in the future (for instance when they are not used for a very long time). 4. Managing videos in a dfferent way than photos is annoying.
I wonder why ancestry does not offer a youtube-like upload service. Maybe they are afraid of abuse and the effort to prevent it. But porn detection software exists on the market so this is not really the point. They could even offer new price models for movie-rich family trees?