I recently had a movie (mkv container) with an opus audio track.
When I try to save the audio track ("Audio / Save Audio")
a dialog pops and offers to save the track as "fileName.*".
If I change the "*" to "opus" and have a look at the generated file
it is of none identifyable content.
Raw opus streams are useless, we don't have means to encapsulate it into an Ogg container as it should be. A nice-to-have, sure.
But for... say... aac streams it does well? ... Saves as aac file...
AAC streams (AAC LC only) are exported as ADTS (audio data transport stream) which is a very simple format. Ogg is much more complex, will need to use libogg for that.