When I set out a few weeks ago to figure out which multimedia player in Debian claimed to support most file formats / MIME types, I was a bit surprised how varied the sets of MIME types the various players claimed support for. The range was from 55 to 130 MIME types. I suspect most media formats are supported by all players, but this is not really reflected in the MimeTypes values in their desktop files. There are probably also some bogus MIME types listed, but it is hard to identify which one this is.
Anyway, in the mean time I got in touch with upstream for some of the players suggesting to add more MIME types to their desktop files, and decided to spend some time myself improving the situation for my favorite media player VLC. The fixes for VLC entered Debian unstable yesterday. The complete list of MIME types can be seen on the Multimedia player MIME type support status Debian wiki page.
The new "best" multimedia player in Debian? It is VLC, followed by totem, parole, kplayer, gnome-mpv, mpv, smplayer, mplayer-gui and kmplayer. I am sure some of the other players desktop files support several of the formats currently listed as working only with vlc, toten and parole.
A sad observation is that only 14 MIME types are listed as supported by all the tested multimedia players in Debian in their desktop files: audio/mpeg, audio/vnd.rn-realaudio, audio/x-mpegurl, audio/x-ms-wma, audio/x-scpls, audio/x-wav, video/mp4, video/mpeg, video/quicktime, video/vnd.rn-realvideo, video/x-matroska, video/x-ms-asf, video/x-ms-wmv and video/x-msvideo. Personally I find it sad that video/ogg and video/webm is not supported by all the media players in Debian. As far as I can tell, all of them can handle both formats.