Free tool

AAC to MP3 converter

Drop a raw .aac file to convert AAC to MP3 in your browser, whether it is a radio recording, a voice recorder app’s file or an export: pick 128, 192 or 320 kbps, or copy the AAC into an M4A without re-encoding it.

  • Free
  • AAC-LC and HE-AAC
  • Nothing is uploaded

Save as

MP3 quality

Plays everywhere. The sound is re-encoded at the quality you pick.

Choose your AAC file

Any audio or video file, up to 1 GB and 2 hours. It’s converted in your browser; nothing is uploaded.

MP3 encoding by LAME, open-source software.

Recorded a radio interview or a talk as .aac? NoteOwl imports AAC files as they are and transcribes them on your Mac, with every speaker labelled.

Download free for MacSend to my Mac

How it works

How do you convert an .aac file to MP3?

Leave MP3 selected and drop the .aac file. The page reads it frame by frame, your browser decodes the AAC, and an MP3 encoder inside the page writes the result at the bitrate you chose. A five-minute stereo file took about three seconds in Chrome. Listen, then download.

  1. 1

    Choose MP3 or M4A

    MP3 for anything that won’t take .aac. M4A to keep the very same AAC sound, unchanged, in the usual AAC file.

  2. 2

    Add the .aac file

    AAC-LC or HE-AAC, mono or stereo: a stream recording, a recorder app’s file or an export.

  3. 3

    Download the result

    Hear it in the page first. The new file keeps the .aac file’s name with its new ending.

How big is the MP3, and how long does it take?

MP3 size follows the bitrate. A five-minute, 5.68 MB stereo AAC file at 160 kbps became 4.8 MB at 128 kbps and 7.2 MB at 192, in three to four seconds. Copying the same AAC into an M4A took under a fifth of a second in both browsers.

5 min, AAC-LC, 48 kHz stereo, 160 kbps, 5.68 MB
Saved asMP3, 128 kbps
Size4.8 MB
Took (Chrome / WebKit)3.4 s / 3.7 s
The same file
Saved asMP3, 192 kbps
Size7.2 MB
Took (Chrome / WebKit)3.1 s / 3.5 s
The same file
Saved asM4A, AAC copied as is
Size5.64 MB
Took (Chrome / WebKit)0.08 s / 0.13 s
1 min, HE-AAC
Saved asMP3, 192 kbps
SizeChrome: 1.44 MB at 48 kHz · WebKit: 1.2 MB at 24 kHz, 160 kbps
Took (Chrome / WebKit)0.7 s / 0.6 s

What is a raw .aac file?

AAC sound with no container around it. An .aac file is an ADTS stream: every short AAC frame begins with its own 7- or 9-byte header giving the sample rate and channels. There is no MP4 wrapper, so no index for seeking, no recorded length and usually no tags.

Many internet radio stations stream AAC this way, so a recording of such a stream is usually an .aac file, and some voice recorder apps and export menus write it too. An M4A holds the same AAC frames inside an MP4 container instead.

Sound
Raw .aac (ADTS)AAC-LC or HE-AAC
.m4aAAC, or Apple Lossless
Around the sound
Raw .aac (ADTS)A small header on every frame
.m4aAn MP4 container with an index
Length and tags
Raw .aac (ADTS)No length; tags rarely
.m4aBoth stored
Typical source
Raw .aac (ADTS)Radio stream recordings, some recorder apps
.m4aiPhone Voice Memos, music downloads

What is the difference between AAC-LC and HE-AAC?

AAC-LC (Low Complexity) is the everyday profile, found in M4A files and most video. HE-AAC adds spectral band replication: the core codes the sound at half the sample rate, and the decoder rebuilds the top octave from a little side information. Many low-bitrate internet radio streams use it.

An .aac file’s frame headers have no way to say HE-AAC. They describe the core as plain AAC at half the rate, and the decoder has to find the extra layer itself. Chrome’s decoder does, and the one-minute file in the table came out at its full 48 kHz. Safari’s plays only the core, so there the MP3 came out at 24 kHz with nothing above 12 kHz, and MP3 limits a 24 kHz file to 160 kbps. For HE-AAC radio recordings, convert in Chrome.

Should an AAC file become an M4A rather than an MP3?

Often, when it is headed for an iPhone, an iPad or a Mac. Choose M4A and the AAC frames move into an MP4 container untouched, with no re-encoding, so nothing is lost and there is no bitrate to choose. Choose MP3 when the destination asks for MP3.

The five-minute file in the table was copied in 0.08 seconds in Chrome and came out at 5.64 MB, against 7.2 MB as a 192 kbps MP3. The quality setting doesn’t apply to a copy. The M4A converter explains what else an M4A can hold.

Can NoteOwl open an .aac file without converting it?

Yes. NoteOwl imports AAC files directly, along with MP3, M4A, WAV, AIFF, FLAC and MP4, transcribes them on your Mac with on-device AI models, labels each speaker and keeps every transcript searchable. Convert to MP3 only for the people and players that need one.

FAQ

Questions about AAC to MP3

Is my AAC file uploaded?

No. The .aac file is read from your own device, decoded by your browser and written as an MP3 inside the page. Nothing is uploaded, and you don’t need an account.

Why does Safari make a 24 kHz MP3 from some AAC files?

Those files are HE-AAC, and Safari’s decoder gives only their core layer, which runs at half the rate. The MP3 then holds nothing above 12 kHz and is capped at 160 kbps. Chrome decodes the full sound, at twice that rate, so convert HE-AAC radio recordings there.

Which MP3 bitrate should I choose?

For speech, such as a talk or a radio interview, 128 kbps: about 0.96 MB a minute. For music, 192 kbps, the default, or 320 kbps. No MP3 setting can restore what the AAC encoder left out.

Can I put the AAC into an M4A instead?

Yes. Pick M4A and the AAC frames are moved into an M4A file exactly as they are: no re-encoding, no loss and no quality setting to choose. A five-minute file took 0.08 seconds in Chrome and 0.13 seconds in Safari’s engine.

Is AAC better than MP3?

AAC was designed to follow MP3 and usually sounds a little better at the same bitrate. MP3’s strength is reach: car stereos, older players and upload forms that turn away an .aac file accept an MP3.

Why won’t some apps open my .aac file?

A raw .aac has no MP4 container, so apps that expect AAC inside an M4A or MP4 may refuse it, and players that do open it have to estimate its length, since nothing in the file records it. An MP3, or the same AAC copied into an M4A, avoids both.

How long a recording can it convert?

Up to 2 hours or 1 GB per file. A two-hour radio recording saved as a 128 kbps MP3 comes to about 115 MB.

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About NoteOwl

NoteOwl is private AI meeting notes and memory for the Mac. It captures meetings without a bot joining the call, labels every speaker, writes summaries and action items, and builds a memory of every conversation that you can chat with — fully offline, because the speech recognition and the AI run on the Mac itself. Dictation into any app is free; Pro is a one-time purchase.

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