So, here are a few tests with folders with one type of file (n<=25 files):
- *.mp3 → files visible, files playable with proper “episode” screen incl. embeded image
- *.opus → invisible, therefore not playable
- *.m4b → invisible (a pity, because m4b is a dedicated format, M4B File Extension - What is an .m4b file and how do I open it?)
3a) renamed *.m4b to *.mp4 → visible, playable but some files no nice episode screen (conversion seems to loose audio book information?) - (other, native) *.m4a → visible, playable with nice “episode” screen
Alright, seems opus and m4b have issues. Anything else I can do to support figuring this out?