External/unoffical commentary track

Some movie critics / enthusiasts do their own commentary tracks for movies, Red Letter Media is a one of many examples. It would be neat if you could just copy such a track to movie folder / subfolder / use {meta descriptions}
Such functionality would also require following sub-functionalities:

  1. Playing (and pausing etc) indicated main and commentary audio tracks simultaneously
  2. Possibility to define delay time of commentary track
    a. by an absolute value
    b. “Start commentary track now” button (for some users it may be more intuitive approach)
  3. Lowering the volume of main audio track (e.g. 25% by default)

Disclaimer: I am able to mix commentary track into movie file on my own, so no need to explain me that (however I really appreciate how helpful this community is). It’s just a hassle which could be automated.

Fantasizing: in the future you could allow to buy commentary tracks from the app directly, which would be nice income stream probably