Once you have decided not to keep audio losslessly, you still have to pick a lossy format. The three that matter in practice are MP3, M4A (which holds AAC audio) and OGG Vorbis. They do the same job — shrink audio by discarding what you are least likely to hear — but they were designed at different times for different reasons, and that shows.

MP3: the one that plays everywhere

MP3 arrived in the early 1990s and became the format that made digital music portable. It is technically the oldest and least efficient of the three, and it is still the right answer more often than not, for one reason: absolutely everything plays it.

Car head units from 2004. Gym treadmills. Cheap MP3 players. DJ software. Voice recorders. Church PA systems. Every phone, every computer, every streaming app. There is no device on which an MP3 will surprise you by not working, and that reliability is worth more than a marginal quality advantage in most real situations.

Its cost is efficiency. At low bitrates MP3 shows its age — below about 128 kbps it audibly struggles where newer codecs cope. At 192 kbps and above, that stops mattering. Convert with the MP3 converter.

M4A (AAC): better sound per megabyte

AAC was designed as MP3's successor and does the job measurably better. At the same bitrate it retains more detail, most obviously in cymbals, sibilance and the top of the frequency range. A 128 kbps AAC file is roughly the equal of a 160–192 kbps MP3.

It is also everywhere you might not expect. Apple built its ecosystem on it, so M4A is native to iPhone, iPad, Mac, the Music app, Podcasts and Apple Books. YouTube uses AAC. So do most streaming services. Android has supported it for many years, so it is not the Apple-only format its reputation suggests.

Choose M4A when the destination devices are reasonably modern, especially if they are Apple's — you get smaller files at the same quality and native handling throughout. The only real risk is older hardware that expects MP3 and nothing else.

OGG Vorbis: open and royalty-free

OGG Vorbis exists because MP3 was encumbered by patents for most of its life and some projects could not or would not pay. It is free, open and unpatented, with quality broadly comparable to AAC and clearly better than MP3 per megabyte.

Its niche is specific but real. Game engines — Unity, Godot, and most audio middleware — treat OGG as a first-class format precisely because there is no licensing footnote. Linux distributions and open-source software favour it. Wikipedia's audio files use it.

For consumer listening it is the weakest choice of the three simply because consumer hardware support is patchier. But if a game engine or an open-source tool asks for OGG, the OGG converter is what you want.

Side by side

Quality per megabyte: AAC ≈ Vorbis > MP3. The gap is significant below 160 kbps and small above it.

Device support: MP3 > AAC > Vorbis, and the gap between MP3 and everything else is what matters when old hardware is involved.

Apple integration: M4A, decisively.

Licensing: OGG is free and open; MP3's patents have now expired; AAC's have not entirely.

Choosing without agonising

If the files have to play on anything you do not control — a friend's car, a community centre's sound system, an unknown device — use MP3 at 192 kbps. If everything is your own reasonably modern kit, especially Apple kit, use M4A at 192 kbps for smaller files at the same quality. If a game engine or an open-source project asks for OGG, use OGG. That is the whole decision.

One thing worth avoiding either way: converting between lossy formats repeatedly. Each pass discards a little more, and the damage accumulates. If you have a lossless source, generate each lossy version from it rather than from another lossy file — the lossless formats guide explains how to set that up, and the bitrate guide covers what setting to use when you do. If you are converting a whole collection in one go, the bulk conversion guide has the workflow.