Hi all. I think for music, admin might just be able to define some categories. But, if he has to define categories for videos, then there will be just too many. What I think should work in that case is tagging. These tags will be search able & also as you type in the search box, you will have tag suggestions popping down. Just like yahoo search engine.
Same way, as you upload your media & start entering your tags, the tag suggestions from already existing tags will start popping down. see more This might just avoid repetitions.
Also admin will be able to view all the tags all via admin section & moderate or alter if required.
Let me know what you all think of this ok.