Compress Audio
Make an audio file small enough to send, by lowering its bitrate.
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or drag them here
MP3, M4A, WAV, FLAC, or OGG
- Takes
- MP3, M4A, AAC, WAV, FLAC, OGG, and Opus — the result is always an MP3, whatever went in. Several at once, all on the same bitrate. AIFF and WMA are not readable in a browser and will be refused.
- Size
- No cap, and nothing is uploaded, so the only ceiling is your own tab's memory. The file is read off disk in pieces rather than loaded whole; a 29 MB, 12-minute MP3 came out the other side in about four seconds. What is held is the new file — at 128 kbps, roughly 1 MB per minute.
Your file never leaves your browser during processing
How it works
To compress an audio file, drop it onto this page and choose a lower bitrate than the one it already has — the expected size is shown before you commit, and the whole re-encode happens in your browser with nothing uploaded.
There is exactly one way to make an audio file meaningfully smaller: spend fewer bits on each second of sound. That is what the bitrate is. A 15-minute recording at 256 kbps is 29 MB; the same recording at 96 kbps is 11 MB. The tool re-encodes your file at the bitrate you pick, and because a constant-bitrate MP3 spends the same number of bits on every second, the expected size can be worked out from the bitrate and the length before anything is processed — it is arithmetic, not a guess, and the finished file lands within about a percent of it.
The important thing to understand is what is being traded. Lowering the bitrate throws away detail permanently, and the encoder chooses what to throw away based on what is hardest to hear. On speech that is very forgiving: a lecture or an interview at 64 kbps mono is perfectly clear and about a twentieth of the size of the original recording. On music it is less forgiving, and the artefacts show up first in cymbals, reverb tails, and applause.
Raising the bitrate is not an option this tool will encourage, because it does nothing. If your file is 128 kbps, encoding it at 320 kbps produces a file two and a half times larger holding the same audio, made marginally worse by the extra pass — the discarded detail is not stored anywhere. The tool reads your file first, shows you the bitrate it actually has, and warns you if the setting you picked is at or above it.
Everything runs in your browser: your file is decoded locally, re-encoded by a WebAssembly MP3 encoder loaded before processing starts, and handed straight back to you. The counter under the tool monitors network activity during the work and stays at zero bytes sent.
FAQ
How small can I make an audio file?
At 64 kbps mono — the practical floor for clear speech — an hour of audio is about 28 MB, against 60 MB at 128 kbps stereo and 600 MB as a WAV. For music, 128 kbps is a sensible floor before the loss becomes obvious.
Why did my file get bigger?
Because the bitrate you chose is higher than the file already had. Re-encoding at a higher bitrate cannot restore detail that was discarded when the file was first made — it only writes more bits about the same audio. Check the bitrate shown when the file loads and pick something below it.
Does compressing audio lose quality?
Yes, and permanently. This is not a zip file — the audio is decoded and re-encoded, and the difference between the two is discarded. If the recording is irreplaceable, compress a copy.
Should I use mono?
For speech, yes: mixing to mono halves the information the encoder has to carry, so 64 kbps mono sounds better than 64 kbps stereo on a voice recording. For music, no — the stereo image is gone for good once the file is written.
What formats can I compress?
MP3, M4A, AAC, WAV, FLAC, and OGG all go in; the result always comes out as MP3, which every device can play. Video files are handled by the extract-audio tool instead.