[PapuaNewGuinea]

Lossy codecs suck at gapless playback. Some have support via vendor-specific extensions, but it’s hit or miss whether a particular player will support it. With FLAC you can always be 100% sure that your album is gapless.

[edflsafoiewq]

That's just MP3, Vorbis and Opus don't have that problem.

[aaaaaaaaaaab]

Nope. Opus and Vorbis are better, but they still don't support 100% gapless playback.

E.g. create a full-scale sine wave, split it into two files, then convert them to "gapless" Opus. Now open the files in Audacity and you'll see that there's a small amount of ringing at the boundary, so it is not truly gapless.

If you try the same with AAC using Apple's gapless metadata (i.e. iTunSMPB) you'll find that the boundary is perfectly continuous.

[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.