Compress audio

Reduce file size by adjusting the bitrate

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What is Compress audio?

This tool reduces the size of your sound files so they fit in an email, send faster or stop filling up your phone. It is especially useful for voice notes, podcasts and long recordings.

You lower the quality just enough with a slider and instantly see how big each file will be. Speech can be reduced a lot without anyone noticing; with music it pays to be more careful.

How to use it

  1. Upload one or more audio files.
  2. Choose the format: MP3, M4A (AAC) or Opus.
  3. Set the bitrate with the slider and, if you like, switch to mono or change the sample rate.
  4. Check the estimated size and click Compress.
  5. Download the files or the ZIP with all of them.

Advantages

Technical details

Audio is re-encoded with ffmpeg to MP3 (LAME), M4A (AAC) or OGG Opus (libopus) at a constant bitrate from 32 to 320 kbps in steps of 8 (Opus is limited to 16–256 kbps). You can force stereo or mono (-ac) and resample to 48, 44.1, 32, 24, 22.05 or 16 kHz (-ar); Opus only supports 48, 24, 16, 12 and 8 kHz, so the nearest one is used. The estimated size is calculated as duration times bitrate and may vary slightly because of the container header. Accepts the usual audio formats and videos, up to 300 MB per file.

Frequently asked questions

How do I reduce the size of an MP3?

Upload it, choose MP3, lower the bitrate (for example to 96 or 64 kbps) and click Compress. You will see the estimated size before processing.

What bitrate should I use for speech?

For speech 48–64 kbps is enough, and in mono it sounds practically the same. With Opus you can go even lower while keeping good quality.

What bitrate should I use for music?

From 128 kbps in MP3 or AAC music sounds good; 192 kbps or more is considered high quality.

Does switching to mono reduce the size?

At a constant bitrate the size is set by the bitrate, but in mono those bits go to a single channel, so you can lower the bitrate without losing quality.

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