Audio Format Cheat Sheet: MP3, AAC, M4A, OGG, and FLAC

Five audio formats cover almost everything you'll ever run into, and most of the confusion around them comes from not knowing which bucket each one falls into. Four are lossy and compressed, built to be small and convenient. One is lossless, built to preserve everything. Here's what each is actually for.

The lossy, compressed family

MP3 is the format everyone's device plays, full stop. It's not the most efficient compressor of the group - AAC beats it at the same file size - but its advantage isn't technical, it's universal. Car stereos from a decade ago, the cheapest MP3 player made, every phone and laptop and smart speaker on the market - all of it plays MP3 without a second thought. When compatibility is the priority over squeezing out the last bit of quality, MP3 is still the safe default.

AAC and M4A are effectively the same underlying format wearing different file extensions, and they're a genuine step up from MP3 in efficiency - better quality at the same file size, or a smaller file at the same quality. This is why Apple uses it as its default (an M4A is what your iPhone's Voice Memos app or GarageBand saves by default) and why YouTube's own audio streams are AAC under the hood. It plays natively and easily on Apple devices and in most modern software; support outside that world is good but not quite as universal as MP3's.

OGG is the open-source entry in the group, developed as a patent-free alternative to formats like MP3. It's common in video games, where it's often used for music and sound effects because of its open licensing, and it shows up in some streaming and voice-chat software too. You'll run into it less often as an end-user download than MP3 or AAC, but it's a solid, genuinely open format where it is used.

FLAC: lossless, for when compression itself is the problem

FLAC is a different category entirely - it's lossless, meaning it compresses the file size somewhat but discards nothing, so the audio decoded back out is bit-for-bit identical to the original. That makes it the right choice specifically for archiving: a recording, a purchased album, anything you want a permanent, exact copy of rather than a compressed approximation. The cost is size - a FLAC file runs several times larger than an MP3 of the same track, closer to WAV than to any of the lossy formats above. For casual listening, that extra size buys you nothing you can reliably hear; for archiving, it buys you the certainty that you kept everything.

A practical picker by scenario

Podcasting: MP3 or AAC, prioritizing small file size so episodes download quickly and don't eat into a listener's data plan - nobody needs lossless audio to hear someone talking into a microphone.

Music archiving: FLAC, if you want a permanent copy that hasn't thrown anything away. This is the one case on this list where the extra file size is actually buying you something real.

iPhone voice memos: M4A is what you'll already have, and there's no reason to convert it unless you're moving the file to a device or app that specifically wants MP3 instead - a lot of car stereos and older hardware are still built around MP3 and can be picky about anything else.

Maximum compatibility: MP3, every time. If you don't know what device or software the file is going to end up on, MP3 is the one format that's played almost everywhere for over two decades running.

Lossy versus lossless, one more time

If this all comes down to one decision: are you listening and sharing, or are you archiving and editing? MP3, AAC, M4A, and OGG are all built for the first case - small, convenient, good enough that most ears can't tell the difference from the original in normal listening. FLAC (and WAV, its uncompressed cousin) are built for the second - exact copies at the cost of file size. Our MP3 vs WAV guide goes deeper into that specific lossy-versus-lossless trade-off if you want the fuller comparison, including when WAV makes more sense than FLAC for editing work specifically.

Converting between them

Whichever format you've ended up with, converting is usually a two-minute fix rather than a reason to re-record anything. Our M4A to MP3 converter handles the most common compatibility complaint - a voice memo or Apple-recorded file that won't play somewhere MP3 is expected - and our MP3 to WAV tool goes the other direction when you need an uncompressed file for editing software. Pick the format that matches what you're actually doing with the file, not the one that sounds the most technical.