Compress audio files online

Frequently asked questions

Is my audio file uploaded?

No. Files are decoded, encoded and measured in your browser; they never leave your device and there is no account. You only get a file when you press download.

How do I make a file fit under a size, like 16 MB for WhatsApp?

Choose "Make it under…", type the size and the page picks the highest bitrate whose estimated size fits, showing the estimate before anything is encoded. MP3 is constant bitrate, so its estimate is within a small margin (tiny clips at very low bitrates can be a few hundred bytes off); Opus and AAC are shown as a range and the highest end must fit. If the real file still comes out over, it is encoded again at a lower bitrate. If the size cannot be reached at all (a long recording and a tiny limit) it says so and tells you the smallest possible size instead of pretending. Sizes use 1 MB = 1,048,576 bytes.

Which format should I choose?

MP3 plays everywhere. Opus (WebM or Ogg) and AAC (M4A) are generally rated better than MP3 at the same small size, especially for speech. The comparison table shows this file's estimated size in every format your browser can write. Opus and AAC need encoders built into your browser; formats it lacks are marked as not supported and are never offered as if they worked.

Is there variable bitrate (VBR)?

Not for MP3: the MP3 encoder used here is constant bitrate only, so MP3 gives you fixed bitrates. For a quality-style choice use Opus, where you pick a level (Voice, Small, Balanced, High, Best) that sets an average bitrate. The size then varies a little around it, which the estimate shows as a range.

Do mono, sample rate or surround settings change the size?

At a fixed bitrate the size depends on the bitrate and length, so mono and sample rate do not shrink an MP3 by themselves; they matter in size-limit mode, where dropping to mono or a lower rate lets a higher quality fit. The page shows the bitrate, sample rate and channels that were really written (for example, a very low bitrate is written at a lower sample rate on purpose, and some bitrates are not allowed at low rates). Surround files are mixed down to stereo with the centre channel kept.

Are the title, artist and cover art kept?

Yes, by default: tags are read from the original (MP3, M4A) and written into the new file (MP3 gets ID3v2.3), and you can strip them or drop just the cover. Cover art counts toward a size limit. A cover over 1 MB is not copied. MP3 files also get the header that lets players skip the encoder's added silence, so playback is gapless.

Can I compress several files at once?

Yes, up to 20. They are processed one after another with their own progress bar and error message, and you can download each file or all of them as one ZIP. If a result is not smaller than the original you can choose to put the original in the ZIP instead.

What does the loudness and dynamics option do?

"Audio compressor" also means dynamic-range compression, which turns down loud parts so the whole recording can be louder and more even. It is optional and off by default, and it does not make the file smaller. You can also set an overall loudness target (-16, -14 or -23 LUFS). Loudness is measured approximately, with a peak limit at -1 dB, so it can stop short of a target.

Can I hear it before I commit?

Yes. "Listen first" encodes a 12-second part of your file with the current settings and lets you switch between the original and the compressed version at the same playback position. By default both are matched to the same loudness, so the louder one doesn't seem better just because it is louder. The preview of the compressed side is decoded by your browser.

What can I open?

MP3, WAV, M4A, OGG and FLAC, or the sound of a video file, as far as your browser can decode them. Your original is never changed.