ZDoom

I have the bad feeling that my understanding of programming isn't enough to get the problem Thanks for trying though

Define 'music's position'. Some formats can loop over certain sections a few times, others don't loop back to the start and so on, and so on. The only reliable thing would be time from playback start, everything else is not really doable unless you have a strictly linear music track, but that info is not known at all.

The depends on what you mean by "Show the current position". Showing is easy, as far as FMod is concerned (although MIDI positions seem a little ambiguous by the looks of it). How you expect to relate that back to setting it in a synchronous environment where music first and foremost runs in an entirely different thread, however, raises some questions.

I also don't know what controls the other sound libraries expose to this, including OpenAL and DUMB.

By the way, what's the most complicated thing about making the Music system show music's position? I still hope that one day it will be possible to make tracker music jump to a certain pattern after current pattern ends/after certain event (in the song).

... not to mention the case where two different and incompatible music backends need to mix their output.

Two music backends would need to be running at once. Furthermore, some midi ports can only operate a single connection at a time. Since ZDoom supports basically any music backend under the sun almost transparently, this becomes a logistical nightmare.

What is so complicated about fading music in and out? I am just curious.

But ZDoom's music system doesn't!

I have seen that this has been suggested already a million times, but why hasn't it been added yet? I mean it's 2015 now and not 1994, FMOD seems to be able to handle this.