[theora] ogg, ogm or mkv

[ogg.k.ogg.k at googlemail.com]

> Matroska has support for chapters, in-file subtitles of different formats,
> multiple (multi-channel) [vorbis] audio tracks (with language identifiers)
> and
> has lower file-format overhead than ogg.

Ogg has always (*) had support for multiple audio tracks (whether
Vorbis or other), language identifiers in the LANGUAGE tag in each
stream's Vorbis comment packet, and new support for subtitles
(both text and image) (and multiple tracks of them too).

Tool support for creation might well be suboptimal, true.

(*) as a first approximation, and probably a second too, but I'm
no Ogg historian.