And then there's the whole Matroska situation, where you have .mkv (video with or without other stuff, any codec), .mka (audio with or without other stuff, but no video, any codec), .mks (subtitles only), .mk3d (stereoscopic video), and debatably .webm (video and/or audio each in one of two specific codecs, generally more opinionated than "regular" Matroska, but probably compatible with a wider range of software).

In principle, you could go through an entire library of multimedia and uniformly encapsulate everything in Matroska, but I'm not sure if there's a point to doing that.