> possibly with a high-quality Theora encoding and highest quality Opus encoding muxed together using the WebM-complaint subset of > Matroska.
WebM is not allowed to contain Theora video, and you wouldn't want to anyway because VP8 is generally speaking better (slower, but better compression for any given quality and not slow enough for it to actually matter that much).
By the way, I must echo the general sentiment. the fact that archive.org supplies a JavaScript-based video player is not a problem if the user can just click on one of the video files and watch it that way, and that archive.org supplies MP4/MP3/etc conversions alongside favorable formats is not a problem. Archive.org is imperfect (my complaint is that uploading videos requires JavaScript), but it's not anywhere near as bad as YouTube and Vimeo and has no problems from a viewing perspective.
