Compress AAC files in your browser
AAC usually sounds better than MP3 at the same bitrate. This writes a plain ADTS .aac stream; choose MP3 instead only when old-player compatibility matters more.
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How to compress an AAC file
The file is read in this tab. It is never uploaded, and a long recording is not stopped by an arbitrary server limit.
Set a bitrate directly or switch on a target size. Turn on mono for speech, and leave it off when stereo placement matters.
The two players let you compare the source and result. Duration, channels, sample rate and the resulting bitrate sit beside them.
The result is an .aac file containing AAC audio in ADTS, produced from memory without a trip through a remote service.
What AAC compression changes
AAC is a lossy audio codec. It removes information the encoder judges less audible, so lowering the bitrate makes a predictable saving but cannot be undone. Re-encoding an existing AAC adds another lossy generation; use the original WAV or recording where you still have it, and use this page when the AAC is the only source left.
At the same bitrate AAC is generally more efficient than MP3, especially below 128 kbps. That does not mean every setting is transparent. Music at 192 or 160 kbps is a cautious reduction, 128 is a practical everyday setting, and 96 or 64 belongs to speech unless a rougher result is acceptable.
The .aac extension here means ADTS: a lightweight sequence of framed AAC audio. It is useful in broadcast and audio pipelines, but old car stereos and desktop applications are more likely to recognise MP3. Apple libraries and consumer music players often prefer the same AAC audio inside an .m4a container instead.
Mono and metadata are separate levers. Downmixing genuinely removes a channel and is sensible only when the channels carry no useful difference. Stripping tags removes titles and artwork rather than sound, so a large cover image can be a free saving while an untagged file changes almost nothing.
AAC compression FAQ
Is AAC better than MP3 at the same bitrate?
Usually, yes. AAC was designed later and tends to preserve transients and high frequencies more cleanly, particularly around 64 to 128 kbps. MP3 still wins for old hardware and software compatibility, so the better format depends on where the file must play.
What is the difference between AAC and M4A?
AAC is the audio codec. This page writes those frames in a small ADTS .aac stream. M4A is an MPEG-4 container that commonly holds AAC and has broader support for library metadata and artwork. The sound can be encoded identically even though the files are wrapped differently.
What bitrate should I choose for AAC?
Use 160 or 192 kbps for music when you want a cautious result, 128 kbps for a smaller everyday copy, and 64 to 96 kbps mono for speech. A second lossy encode always has a cost, so begin with the highest setting that meets the real size limit.
Can AAC compression be lossless?
No. AAC is a lossy codec, and changing its bitrate discards information. Removing a cover image or text tags is lossless with respect to the sound, but it does not make the audio frames themselves smaller.
Can I make an AAC fit a specific attachment limit?
Yes. Switch on the target control and enter the limit in kilobytes. Constant bitrate makes size mostly a duration calculation, so the page chooses the highest supported bitrate under the figure and tells you when even 32 kbps cannot fit.
Does the file leave my device?
No. Mediabunny and the AAC encoder run in this browser tab. The encoder code is downloaded when it is needed, but your recording is not sent back with that request or stored on a server.
Can this compress AAC audio inside a video?
No. This is an ADTS audio tool, not a video editor or an audio extractor. Video compression belongs at vidshift.io, where the container, picture and soundtrack can be handled together.
Related
Same format joins the queue. Anything else re-routes to its own tool.