Library & files
Ogg and Opus
Ogg is an open container, usually holding Vorbis audio; Opus is a newer open codec that outperforms both at low bitrates. Both are lossy, both are free of licensing, and neither is standard in DJ software.
In practice
Good codecs, wrong ecosystem. If an Ogg or Opus file matters, buy it properly in a format your players read.
Do not transcode either into MP3 to make it play — you are stacking a second lossy encode on top of the first and the result is worse than both. Buy the track from a store instead, which gets you a clean file, correct tags and something the booth will definitely load. If you must carry one, test it in an actual player well before the gig rather than assuming firmware support you have not verified.
Lossy
Both of them
Not standard
In DJ hardware
Never transcode
The move that makes it worse
Where these come from: Codec characteristics and current DJ hardware support — published specifications, not catalog figures. For what we can measure, see what a second encode costs.
Why it matters
They are technically good and practically marginal. Opus in particular is better than MP3 at the same bitrate by any measure, but stores do not sell it, club players do not universally read it, and a format your gear might refuse is a format that costs you more than it saves.
Where they do turn up is in files pulled off the open web or out of a game or streaming source, which is exactly the material most likely to arrive without a clean provenance. The format is not the problem there; the source is.
Frequently asked
Can CDJs play Ogg or Opus files?+
Support is inconsistent and firmware-dependent, which makes them a bad bet for a booth. Test in a real player before you rely on one, or convert the source properly by buying it.
Is Opus better than MP3?+
At the same bitrate, measurably yes, especially low down. That does not help if the store does not sell it and the player will not read it.
Should I convert Ogg files to MP3?+
No. That is a lossy file encoded lossily again, which discards more than either step alone. Buy the track instead.
Related terms
Lossy compression
Lossy compression shrinks a file by discarding audio a listener is unlikely to notice. What it removes is gone permanently, and encoding an already-lossy file removes more on top.
Variable bitrate
Variable bitrate spends more data on complex passages and less on simple ones, so quality stays even and file size varies. Constant bitrate spends the same everywhere, so size is predictable and quality is not.
AAC and M4A
AAC is a lossy codec, usually delivered in an .m4a container, and it is what Apple’s ecosystem and most video use. At the same bit rate it generally holds up better than MP3.
Bit rate
Bit rate is how much data one second of audio uses, in kilobits per second. It decides the file size, and on a lossy format it decides how much of the original recording survives the encoding.
Explore: Audio quality checker · Lossy compression · Bitrate · All DJ terms