What is MP3?

MP3 is a lossy audio format that discards frequencies the ear is least likely to notice. Its patents expired in 2017, and it remains the audio file that plays on absolutely everything.

MP3 at a glance

MIME type: audio/mpeg
File extensions: .mp3
Specification: MPEG-1 and MPEG-2 Audio Layer III, ISO/IEC 11172-3 and 13818-3
Compression: Lossy. Bitrate sets the trade: 128 kbps for speech, 192 kbps as a general default, 320 kbps as the practical ceiling.
Transparency: Not applicable.
Animation: Not applicable.
Colour depth: Not applicable. Sample rates up to 48 kHz, mono or stereo.
Metadata: ID3v1 and ID3v2 tags: title, artist, album, cover art.
Support: Universal, including car stereos, older phones and hardware players that reject everything else.

Strengths and weaknesses

Plays on every device ever built with a speaker and a file browser.
Small files: an hour of speech at 128 kbps is around 55 MB.
No licensing questions remain now that the patents have lapsed.

Modern codecs such as Opus and AAC sound better at the same bitrate.
No multichannel audio in ordinary use.
Re-encoding an MP3 into another MP3 compounds the loss.

Choosing a bitrate

For a podcast, a lecture or any spoken recording, 128 kbps is transparent enough and keeps the file small. For music extracted from a video, 192 kbps is the usual balance and 320 kbps is worth it only if the source was high quality to begin with.

Extracting audio from a compressed video cannot exceed the quality already in that video. If the clip was encoded with 128 kbps AAC, asking for 320 kbps MP3 produces a larger file containing exactly the same sound.

Working with MP3 files

Convert to MP3

MP4 to MP3Extract audio as MP3