I think we should enable support to upload Matroska and WebM (WebM being a profile of Matroska, using VP8 video and Vorbis audio).
Matroska files are much more suitable for re-use (especially editing) than already supported OGG container format.
File extensions/mime types for Matroska:
.mkv video/mkv video/x-matroska
File extensions/mime types for WebM: