Performance Video and sound. One thing I have already learned from collecting this material is that items most likely to be made available are those that are generated in the normal development of a performance. Directors and designers are busy people, and are unlikely to be willing to spend additional time writing or typing. Films and commercial releases of music tracks are formidably difficult to obtain copyright information about, let alone getting permission to use them. This solution will clearly not work for an Internet site.
Stage productions offer more promise, though the difficulties here are still significant.