Compress audio
Shrink recordings, podcasts and songs to send or store. Done on this device, never uploaded.
- Nothing is uploaded
- Works offline after first use
- Open source
- No watermark · limit is your device’s memory; phones hold less
Makes MP3, WAV, M4A and other audio files smaller, or fits them under 8, 16 or 25 MB. 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
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.
How it works
- Drop one or more audio files (MP3, WAV, M4A, FLAC, OGG), or tap to pick them.
- Choose how hard to compress, or a size limit such as 25 MB for email. Tick Mono for a voice recording.
- Compress. One file downloads straight away; several download as a zip.
In your browser, not on a server
Your browser decodes the sound with its own audio decoders. When you set a size limit, the bitrate is worked out from the length of the sound so the file lands under it. The smaller file is then written in your tab, as MP3 by LAME compiled to WebAssembly or as OGG by the browser’s own Opus encoder (WebCodecs) with Mediabunny (MPL-2.0) writing the container.
Compared with upload-based tools: Online audio compressors upload the recording before they shrink it, which for a large WAV is the slowest part, and cap free files at 50 to 100 MB. Here nothing is uploaded, so the limit is your device’s memory (phones hold less) and private recordings stay on your device.
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
Are my files uploaded?
No. Your browser decodes the sound and the smaller file is written inside the page: MP3 by LAME compiled to WebAssembly, OGG by the browser’s own Opus encoder. Your files are not uploaded, so the size limit is your device’s memory (phones hold less), and the page works offline after one visit and a short wait (MP3 output needs one MP3 run first).
How much smaller will it get?
A WAV shrinks to about a tenth at 128 kbps. An MP3 that is already 320 kbps drops to about 40%, and one at 128 kbps only gets smaller at a lower setting. If a file is already smaller than the setting would make it, you get it back unchanged.
How does Fit under work?
It works out the bitrate that brings the file under the limit from its length, and uses that when it is lower than your chosen setting. An hour of audio needs about 48 kbps to fit in 25 MB, fine for speech. Tick Mono as well for recordings of talk.
MP3 or OGG?
MP3 plays everywhere. OGG with Opus sounds better at low bitrates, so a voice memo at 48 kbps Opus is as clear as a 96 kbps MP3; Chrome, Firefox, Android, Discord and WhatsApp play it, older iPhones may not.
More video and audio tools
Pitch and speed changer
Change the key of a song, or play it faster or slower, keeping the other the same. Done on this device.
BPM and key finder
Drop an audio file and read its tempo, key and Camelot code. The song is analysed on this device.
Online tuner
Play a note and see how sharp or flat it is. Guitar, bass, ukulele, violin or chromatic, with the sound kept in your tab.
Metronome
A steady click at any tempo, with the bar, the subdivisions and tap tempo, running on your device.
Popular conversions
Guides
- 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.