Audio Compressor
Shrink audio files by lowering the bitrate or switching format. Runs in your browser, nothing is uploaded.
Everything runs in your browser. Your audio is never uploaded, and nothing is stored.
How to use it
Drop one or more audio files onto the box, or tap it to pick them. Format decides the codec. MP3 plays everywhere and is the safe default. M4A is AAC, which sounds better than MP3 at the same bitrate. Opus is smaller still at low bitrates but older players will refuse it. Bitrate is where the saving comes from. 128k is transparent enough for music on most speakers. 64k is fine for speech. 32k is phone-call quality and should only be used for voice notes. Mono halves the size of anything that does not need stereo, which covers most spoken recordings. The first run downloads a 31 MB engine. That happens once and is then cached.
Questions
Is my audio uploaded anywhere?
No. The whole thing runs inside your browser using a WebAssembly build of ffmpeg. The files never leave your device, which is why there is no size limit and no sign-up.
What bitrate should I use?
128k for music, 64k for speech, 32k only for voice notes where size matters more than clarity. Every step down is roughly half the file size.
Which format is smallest?
Opus, by a wide margin at low bitrates. The catch is support, so use M4A if the file has to play on older hardware and MP3 if it has to play on anything at all.
Can I make an already compressed file smaller?
Yes, but it is re-encoded from the compressed version, so the losses stack. Going from a 128k MP3 down to 64k works, it just will not sound as good as encoding 64k from the original.
Does Mono hurt music?
It collapses the stereo image, so yes for music. For interviews, podcasts and voice notes it is usually free size with no real loss.