How to compress an audio file

Audio file size depends mostly on bitrate and length. Choosing a sensible bitrate can shrink a file by 90% or more with little audible difference. Here is how to pick one.

By 孤獨的時空旅人 · Updated 2026-10-16

Bitrate and file size

File size in bytes is roughly bitrate in bits per second times seconds, divided by 8. A 3-minute song at 96 kbps is about 2.2 MB, and one minute at 128 kbps is about 0.96 MB. A one-hour podcast at 64 kbps in mono is about 28.8 MB. Uncompressed WAV is far larger, so converting a WAV file saves the most.

Which bitrate to choose

For music you care about, 128 to 192 kbps is close to the original for most listeners. For speech and podcasts, 64 to 96 kbps is usually fine, and 48 kbps suits short voice notes. Go lower only if you accept audible loss, because every re-encode of a lossy file reduces quality a little.

When mono helps

Speech recorded with one microphone does not need two channels, and mono roughly halves the size. Keep stereo for music, where the left and right channels differ.

AAC and Opus

The Audio Compressor saves AAC in an .m4a file, which plays on phones, computers and most players. If your browser cannot encode AAC it saves Opus in an .opus file instead. MP3 output is not provided.

Do it privately

The file is decoded and re-encoded in your browser with WebCodecs, so recordings of meetings, lessons or interviews are not uploaded. Very long files can be slow on phones; compress on a computer when you can.

Tools used in this guide

Audio CompressorMake audio files smaller (AAC)Extract Audio from VideoSave the soundtrack as M4A Add Music to VideoBackground music with volume and fades Remove Silence from VideoCut silent pauses automatically

Frequently asked questions

How do I estimate the size?

Multiply the bitrate in bits per second by the length in seconds and divide by 8. For example 96 kbps for 180 seconds is about 2.2 MB.

What bitrate is good for podcasts?

64 to 96 kbps, and mono if there is a single speaker.

Can I get an MP3?

No. The output is AAC (.m4a), or Opus if your browser cannot encode AAC.

Is my audio uploaded?

No. It is processed in your browser.

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