Audio tool
Audio Compressor
Shrink an audio file to MP3, AAC, Opus or FLAC at a bitrate you pick, in seconds.
Your audio stays on this device. The MP3 encoder runs in this browser, so the file is never uploaded.
That costs you three formats. M4A, OGG/Opus and FLAC needed encoders a browser does not have, so they are gone rather than offered and broken. MP3 and WAV are what most people want when they are shrinking a file anyway.
Choose your file
Choose the output
Which bitrate to pick
128 kbps is the default because it is transparent enough for most listeners on most equipment, and it roughly quarters a CD-quality WAV. Use 192 or 320 for music you care about, or if you will edit the result further.
64 kbps is for speech: a recorded lecture, an interview, a voice memo. Music at 64 sounds watery. Speech at 64 is fine and the file is half the size again.
Dropping the sample rate as well as the bitrate is worth trying for speech. 22.05 kHz at 64 kbps produces a remarkably small file that still reads clearly, because speech does not use anything above 11 kHz.
Choosing a bitrate that suits what you are listening to
MP3 throws away detail the encoder predicts you will not notice, so the useful question is where your material sits. Speech is forgiving: an interview, a lecture recording, or a podcast holds together well at a modest bitrate because the ear needs less precision for voice than for music.
Music with cymbals, strings, or layered synthesis is where low bitrates show first, usually as a watery shimmer around high frequencies. If the recording is something you will listen to repeatedly or play on a good system, stay at a higher bitrate and accept the larger file. If it is a voice memo you will play once, the smaller file is the better trade.
A constant bitrate keeps the file size predictable, which is what you want when the destination has a hard limit. A variable bitrate spends its budget where the audio is complex, so it usually sounds better at the same average size but gives you a less predictable total.
Do not re-encode an MP3 to a lower bitrate expecting a smaller file with the same quality. The loss has already happened once, and every further pass adds another round of it, so always start from the original recording if you still have it.
Further reading: Read the full guide: Audio Compressor
Common questions
Is my audio uploaded?
No. The MP3 encoder (LAME, compiled to WebAssembly) runs in this page, so your audio is never uploaded. Everything happens on your device and nothing is left behind afterwards. Encoding is slower here than it would be on a server, which is the cost of not sending the file anywhere.
Which formats can it produce?
MP3, AAC or M4A, Opus in an Ogg container, FLAC and WAV. MP3 and AAC are lossy and will be smaller. FLAC is lossless but still compresses well on most audio. WAV is uncompressed, so converting to it makes the file bigger, not smaller.
Will it definitely make my file smaller?
No, and it will tell you when it does not. WAV is uncompressed, so WAV to WAV comes out about the same size. Re-encoding an MP3 that is already at the bitrate you are asking for is measurably worse than the first pass, because you are throwing away detail that cannot be recovered. The page shows the real difference, and says so plainly when the result is bigger.
How much smaller should I expect?
It depends entirely on the source and the bitrate you choose. A WAV recording converted to 128 kbps MP3 typically drops by well over 80%, because uncompressed audio is enormous. Already-compressed MP3 has far less to give — maybe 10 to 20% at a lower bitrate, and nothing at all at the same one. The page estimates the result before you convert, so you can see what your file will weigh first.
Is there a limit on the file?
40 MB. MP3, WAV, M4A, AAC, OGG, Opus, FLAC, AIFF, WMA, WebM and AMR are all accepted, up to that size. Anything larger is refused before the upload begins rather than partway through.