How do I convert MP3 to AAC?

Drop the MP3 onto the converter at the top of this page, keep 128 kbps or choose another AAC bitrate, press Convert to AAC and download the .aac file. It works in your browser with no software or account, for files up to 100 MB and 30 minutes, as long as the browser has an AAC encoder.

What is the difference between .aac and .m4a?

Both contain AAC audio. An .aac file is the raw stream, frame after frame with a short ADTS header on each; an .m4a wraps the same audio in an MP4 container with an index and tags. Apple apps and most phones prefer .m4a; some car stereos, older players and streaming tools ask for .aac.

Will my car stereo play the .aac file?

It depends on the stereo. Look for .aac or AAC in the manual's list of playable files: some units read .aac but not .m4a, some the reverse, and some read neither. If yours only plays MP3, keep the MP3; the AAC to MP3 Converter on this site handles the reverse trip.

Does converting MP3 to AAC improve quality or save space?

It does not improve quality: the AAC can only keep what the MP3 already has. It saves space only if you pick a lower bitrate than the MP3, for example 96 kbps mono for a voice recording. At the same bitrate the .aac is about the same size as the MP3.

Is the MP3 uploaded anywhere?

No. Decoding the MP3, encoding AAC and adding the ADTS headers all happen in your browser, so the audio never reaches ParrotNotes or anyone else. The page counts ordinary events such as the bitrate chosen, never the file or its name.

MP3 to AAC Converter

Make a plain .aac file from an MP3, for a car stereo, an older player or any program that asks for .aac rather than .m4a. Pick a bitrate and download. Free, no sign-up, and the conversion happens on your device.

Checking whether this browser can encode AAC…

Drop your MP3 here or click to browse

MP3, WAV, M4A, OGG, FLAC, Opus or WebM, up to 100 MB and 30 minutes.

The file is converted in your browser and is not uploaded.

How to convert MP3 to AAC

One file at a time. WAV, M4A, OGG, FLAC and other files your browser can play work as well.

1
Drop the MP3
Drag it onto the box above or click to choose it. The page checks first that this browser can encode AAC, then shows the file's length and the size the .aac will be.
2
Pick a bitrate
128 kbps is the default and suits most MP3s and speech. Choose 192 or 256 for music, and switch on mono for a one-voice recording to halve the size.
3
Save the .aac
The audio is decoded, encoded as AAC-LC and written frame by frame with an ADTS header in front of each frame. Listen to the preview, then download it with the same name and an .aac ending.

.aac or .m4a: same sound, different wrapper

Both hold AAC audio, and at the same bitrate they sound the same. The difference is packaging: an .aac file is the bare audio stream, while an .m4a puts that stream inside an MP4 container.

	.aac (ADTS)	.m4a (MP4)
Audio inside	AAC	AAC (or Apple Lossless)
Structure	A run of frames, each with a 7-byte header	Boxes: a header with an index, then the audio
Length and seeking	Not stored; players count or estimate	Stored in the header; seeking is exact
Title, artist, cover	No standard place for them	Stored in the file
Typical use	Streams, encoders, players that list .aac	Apple Music, iPhone, most phone apps

MDN describes ADTS as AAC audio with a small header on every frame, meant for streaming; M4A is the audio-only form of the MP4 container.Adding the file to Apple Music, iTunes or an iPhone? Use the MP3 to M4A Converter instead: Apple's apps expect AAC inside an .m4a.Need to go the other way? The AAC to MP3 Converter turns .aac and .m4a files back into MP3s.

When you need a plain .aac file

Most of the time an .m4a is the better AAC file. These are the cases where the bare stream is what is asked for.

Car stereos and head units
Some head units and USB media players list .aac as a supported file type and skip .m4a, or the other way round. Check the manual's list of file types; if it names .aac, this is the file to copy to the stick.
Older portable players
Some older MP3 players and Bluetooth speakers with a card slot read AAC only as a raw stream. A bare .aac is the simplest AAC file such a device can be given.
Streaming and broadcast tools
Internet radio encoders, playout software and some video tools take or send AAC as an ADTS stream. A ready .aac file can go straight into that kind of pipeline without a container to strip.
Upload forms and app pickers
Some web forms, editors and phone apps name .aac in their list of accepted files and grey out everything else. Converting gets the recording through the picker.

Converting MP3 to AAC will not improve the sound

An MP3 has already thrown away part of the original audio. AAC encodes what is left, so the .aac cannot sound better than the MP3, and a second lossy encode can lose a little more.

Keep that loss small by choosing an AAC bitrate at least as high as the MP3's: 128 kbps for a typical 128 kbps MP3, 192 or 256 for music you care about. Going above the source only makes the file larger.

Convert because a device or program wants .aac. Keep the MP3 as well, and if you still have the original recording or a WAV, convert that instead.

How big the .aac will be

AAC at a set bitrate grows by the same amount each second, and each frame adds its 7-byte header, about 0.3 KB a second at 44.1 kHz. The converter shows the size for your file before you start.

AAC bitrate	Per minute	Per 30 minutes
96 kbps	721 KB	21.1 MB
128 kbps	955 KB	28.0 MB
192 kbps	1.4 MB	41.7 MB
256 kbps	1.8 MB	55.4 MB

At a fixed bitrate a mono file is the same size as a stereo one; mono spends all the bits on one channel, so speech can drop to 96 kbps. Real files land within a few percent of these figures. 1 MB = 1,048,576 bytes.

Which browsers can write .aac

The page uses the browser's WebCodecs audio encoder with AAC, the same encoder as our MP3 to M4A page, and checks it when the page opens. If your browser has no AAC encoder, the page says so and does not hand you a different format.

Browser	WebCodecs audio encoder	AAC on this page
Chrome on a computer	Version 94 and later	Yes, our AAC encoder was tested on a Mac
Edge	Version 94 and later	Checked on load
Safari on Mac, iPhone and iPad	Version 26 and later	Checked on load
Firefox on a computer	Version 130 and later	Checked on load
Firefox on Android	Not available	No

The version numbers come from MDN's browser compatibility data. Whether the encoder includes AAC depends on the browser and the device.

Changing formats is a detour. ParrotNotes starts with the recording.

You are changing a file's format so a device will take it. ParrotNotes records on your phone and hands you the transcript and a summary of the recording, free for 100 minutes of recording a month.

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Related tools

MP3 to AAC FAQ

Sources

MP3 to AAC Converter

How to convert MP3 to AAC

Drop the MP3

Pick a bitrate

Save the .aac