Convert AAC to MP3 in your browser

For the player, editor or upload form that will not read a bare .aac stream. AAC is the better codec, so this is about compatibility rather than quality.

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AAC to MP3 options

Bitrate (kbps) 192

Your AAC is already lossy and MP3 is the weaker codec, so matching the source number would lose more than it appears to. 192 is the default for that reason. For speech from a recorder or a dash cam, 96 with mono is plenty.

Downmix to mono Off

One channel instead of two. Recorders, dash cams and stream rips of talk content are frequently the same signal twice, and this halves the file with nothing lost.

Strip tags and cover art Off

Off by default, though a raw ADTS stream often carries no tags to begin with. Where one has an ID3 block in front of the audio, it is carried into the MP3 unless you turn this on.

Convert to a target size Off

MP3 size is bitrate times duration, so we work the bitrate out from the length of the recording. A long stream rip is exactly the case where a fixed figure is easier to reason about than a bitrate.

How to convert AAC to MP3

01

Drop the AAC files

Stream rips, recorder output, dash cam audio, anything with a bare .aac extension. The duration is measured from the packets rather than trusted from a header that ADTS does not have.

02

Pick a bitrate

192 keeps a second lossy pass from being audible on music. For speech, drop to 96 and turn on mono, which usually sounds identical and is a quarter of the size.

03

Save the MP3

A .mp3 with proper framing that Windows, car stereos, DAWs, podcast hosts and every upload form accept without needing to know what ADTS is.

Why will nothing open my .aac file?

Because it is not a container. An .aac file is normally a raw ADTS stream: AAC audio frames each carrying a small header, one after another, with nothing wrapped around them. There is no index, no duration field and usually no metadata, which is why players show it with an unknown length, why seeking jumps around, and why plenty of editors and upload forms refuse it outright. The same audio inside an .m4a would be accepted everywhere, because that is an MP4 container with all of those parts.

MP3 is the other kind of file that solves this, and it solves it more thoroughly. It is also a stream of frames rather than a container, but it is the format every piece of audio software on earth has handled for thirty years, complete with the conventions for tags, VBR headers and duration that grew up around it. That is the entire trade this page makes: you move from the better codec to the one nothing refuses.

Because the source is already lossy, this is a second encode over audio that has had detail removed once, and AAC being the stronger codec means matching its bitrate in MP3 would lose more than the number suggests. That is why 192 is the default rather than whatever your file reports. If the audio came from a recorder that can also write WAV or M4A, recording in one of those and skipping this page entirely is the better answer.

AAC to MP3 FAQ

Why does my .aac show the wrong duration before converting?

ADTS has no duration box for a player to read, so most software estimates one from the file size and the first frame, which is wrong whenever the bitrate varies. This tool scans the packets instead, which is why the length shown here is the real one.

Is AAC better than MP3?

Yes, at the same bitrate, especially below 128 kbps. That is the cost of this conversion and the reason the default sits at 192 rather than matching your source. You convert because something will not play the AAC, not because MP3 sounds better.

What about .m4a files, are they the same thing?

The audio usually is, but the file is not. An .m4a is AAC inside an MP4 container, with the duration, seeking and metadata a bare stream lacks. It has its own page here, because the two need different explanations even though the codec matches.

Can I convert a long recording or a whole folder?

Yes. Drop the folder and every file queues with the same settings. Nothing is uploaded, so a two hour stream rip is limited by your own machine rather than by anyone's file size rules.

Will the quality drop?

A little, and unavoidably: this is a second lossy encode. At 192 kbps from a normal AAC the difference is very hard to hear on music, and for speech at 96 kbps mono it is inaudible on a phone or a car speaker.

Are my AAC files uploaded to convert them?

No. The AAC is decoded and the MP3 is written by your own browser, in this tab. There is no upload endpoint in the site for a file to go to, which you can check in your network tools: convert something and watch that no request carries it. Disconnect from the network after the page loads and it still works.