Library & files
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.
In practice
AAC beats MP3 at the same bit rate — the reason to prefer MP3 anyway is that every club player reads it.
Check what is actually inside an .m4a before assuming: AAC is lossy and ALAC is lossless, and the extension does not distinguish them. If a track only exists as AAC, converting it to MP3 for the stick means re-encoding something already lossy, which loses a little more — so carry the AAC if the player reads it and convert only when you have to.
Lossy
What AAC is
AAC or ALAC
What .m4a can contain
MP3
What every player reads
Where these come from: Format properties and player conventions, not catalog figures. For what we can measure, see why re-encoding costs you.
Why it matters
The confusion worth clearing up is that .m4a is a container rather than a codec. What is inside is normally AAC and occasionally ALAC, which is lossless — so two files with the same extension can be very different things, and only the file’s details tell you which you have.
For a DJ the reason to prefer MP3 anyway is not quality but reach. Every club player and every piece of DJ software reads MP3 without question, and a format that is technically better and occasionally unreadable is worse in a booth.
Frequently asked
Is M4A the same as AAC?+
Not quite. M4A is the container; AAC is the codec usually inside it. The same container can hold ALAC, which is lossless, so the extension alone does not tell you what you have.
Is AAC better than MP3?+
At the same bit rate, generally yes. That advantage is smaller than the compatibility advantage MP3 has in a booth, which is why most DJ libraries are MP3 regardless.
Can DJ software play M4A?+
Most can, and support has improved a lot. Club players are the weaker link, which is the argument for keeping the set itself in a format nothing refuses.
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.
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.
Lossless
Lossless means the encoding discards nothing: decode the file and the original samples come back bit for bit. WAV, AIFF, FLAC and ALAC are lossless; MP3 and AAC are not.
FLAC
FLAC is a lossless compressed format: it shrinks a file without discarding any audio, so decoding returns the original samples exactly. It typically lands around 60% the size of the WAV it came from.
Explore: Lossy compression · Browse the catalog · Bit rate · All DJ terms