Convert MP3 to AAC
Re-encode MP3s as AAC audio in .m4a files, on your own device.
- Nothing is uploaded
- Works offline after first use
- Open source
- No watermark · limit is your device’s memory; phones hold less
Convert MP3 to AAC in your browser. It is free, needs no account and adds no watermark, and your files are not uploaded: everything runs in your browser on your device. The size limit is your device’s memory, and phones hold less; give the page a short while after your first run to save itself for offline use, and then it works offline.
Done
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Open the network tab. Your files never appear in it.
Add files and run the tool to see every request this tab makes.
Your files are processed on this device and never sent to a server. Reload the page to clear everything from memory.
AAC is the codec that succeeded MP3. At the same bitrate it usually sounds a little cleaner, and it is what Apple Music, YouTube, iPhone voice memos and most streaming services use. This page decodes each MP3 in your browser and re-encodes it as AAC-LC with the browser’s own encoder. Nothing is uploaded.
The file you get is an .m4a: AAC audio inside an MP4 container. That is the normal way to ship AAC as a file, and iPhones, the Music app, Android, Windows and VLC all play it. A bare .aac stream is rarer and many players and video editors handle it worse, so the page does not write one.
Converting from MP3 cannot add quality, because the detail the MP3 threw away is gone. 192 kbps AAC keeps what a 256 or 320 kbps MP3 had; for a 128 kbps MP3 or a podcast, 128 kbps AAC is enough and the file stays small. The output is written at 48 kHz, the rate browser AAC encoders work at.
If you only need the file for an iPhone or iTunes, the MP3 to M4A page covers the same conversion with notes on ringtones and the Music app.
How it works
- Drop one or more MP3 files, or tap to pick them.
- AAC at 192 kbps is already chosen. Use 128 kbps for speech.
- Convert. Each .m4a downloads when it is ready; several come as a zip.
In your browser, not on a server
Your browser decodes the sound with the decoders it uses to play media on any website. The new file is written in your tab: MP3 by LAME compiled to WebAssembly, WAV by a few lines of code, FLAC by a small lossless encoder in this site’s code (fixed predictors and Rice coding, as the FLAC format describes), and M4A or OGG by the browser’s own AAC and Opus encoders (WebCodecs), packed by Mediabunny (MPL-2.0). WAV and FLAC keep the original sample rate.
Compared with upload-based tools: Online audio converters upload every file, queue it, cap free use at a few files or a few hundred megabytes, and keep the upload for hours. Recordings of meetings, unreleased songs and voice memos are private. Here the files never leave your device and a whole folder converts at once.
Verify it yourself. Give the page a short while after your first run to save itself for offline use, then turn off Wi-Fi or switch to airplane mode and run the tool again. Or open your browser's developer tools (F12, or Cmd-Option-I on a Mac), pick the Network tab, and watch it while you convert. The panel above does the same count for you.
Questions
Why is the file .m4a and not .aac?
AAC is the codec, and .m4a is the usual file for it: the same AAC audio wrapped in an MP4 container that carries a duration and seeks properly. You can rename .m4a to .m4b for an audiobook, but nearly every player treats it as the AAC file you wanted.
Does it work in Firefox?
Browsers borrow the operating system’s AAC encoder, and Firefox, like Chrome on Linux, does not have one it can use. Open the page in Safari, or in Chrome or Edge on Windows or Mac.
Is AAC better than MP3?
From an original recording, AAC sounds a little better than MP3 at the same bitrate. From an MP3 it keeps the MP3’s quality and never more, and each lossy conversion costs a little. Keep your MP3s as the originals.
Are the title, artist and cover art kept?
No. The .m4a is written from the decoded sound, so the MP3’s tags are not copied across. Add them in your music app after importing.
Is the file uploaded anywhere?
No. There is no server in this process. The page is a static file and the work is done by code running inside your browser tab. Give the page a short while after your first run to save itself for offline use; then you can turn off Wi-Fi and it still works.
More video and audio tools
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Video to AVI
Turn MP4, MOV, WebM and MKV files into AVI files. Converted on this device, not uploaded.
Video to WebM
Turn MP4, MOV and MKV files into WebM with VP9 video and Opus sound. Converted on this device, not uploaded.
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Guides
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- How to merge audio filesJoining voice notes, podcast segments or songs end to end is simple once you know the right tool. Here is the desktop way and a private browser way.
- How to reduce MP3 sizeAn MP3 gets smaller when you lower its bitrate, make it mono, shorten it, or switch format. Here is what each saves, with measured results.