[edflsafoiewq]

AFAIK iTunSMPB just tells you where playback should start/end, which is also all the Ogg metadata does for you. MP3s can have iTunSMPB too, it's just a matter of if a player supports it. Is there any specific feature of AAC that makes gapless playback possible?

[aaaaaaaaaaab]

Nope, there’s nothing special to gapless playback. But as it stands, libopus cannot produce truly gapless files right now. Is it a bug in libopus? Most likely.