Question

On iOS, why can the Jellyfin app play Opus music fine, but Finamp cannot without forcing transcoding to AAC in Finamp settings?

Details

I recently lossy-encoded my FLAC music library to Opus format and created a new library for it on my Jellyfin server. I started trying to use the Jellyfin iOS app to play music from the library, which works fine with one caveat: if the phone screen locks, the next track in the queue will not play. This seems to be related to a limitation in a library used for the Jellyfin iOS app (expo).

The only workaround I am aware of to continue playing music from a Jellyfin server on iOS after the screen locks is to use the Finamp app instead, which is a purpose-built music player app for Jellyfin servers. But it will not play Opus tracks on iOS, apparently because iOS doesn't natively support Opus except when it's in a CAF container, which is non-standard and exceedingly rare. I have to set Finamp to transcode all music to AAC in order to play the tracks.

Why can the Jellyfin app play Opus tracks on iOS without issue, but Finamp can't?