MP3 (MPEG-1 Audio Layer III)

MP3 is the format that put a thousand songs in your pocket. It compresses audio down to roughly a tenth of the original size while still sounding good to most ears, which is why it took over music in the late 1990s and never really left. Two decades later it is still the safest bet when you want an audio file that will open anywhere.

An MP3 file is lossy compressed audio. It uses a psychoacoustic model, a set of rules about what the human ear can and cannot hear, to throw away the parts of the sound you are least likely to notice and keep the rest. The amount it keeps is set by the bitrate. A 320 kbps MP3 keeps a lot and sounds close to the source. A 128 kbps MP3 keeps less and saves space.

Development started in the late 1980s at the Fraunhofer Institute in Germany and was standardized as part of MPEG-1 in 1991, then MPEG-2 in 1993. It exploded with the rise of file sharing and portable players around 1999 to 2001. The core patents expired in 2017, so MP3 is now free to use, which only cemented its place as the universal audio format.

MP3 stores audio as a sequence of short frames, each independently decodable, which is why you can start playing an MP3 from the middle. Encoding can be constant bitrate (CBR), where every second uses the same data, or variable bitrate (VBR), where quiet or simple passages use less. VBR usually gives better quality per megabyte. ID3 tags at the start or end of the file hold the title, artist, album, and cover art.

• Music libraries and players
• Podcasts and spoken word
• Sharing audio where it must open on any device
• Anywhere small file size matters more than perfect fidelity

Everything plays MP3: phones, browsers, cars, smart speakers, every operating system. It is the closest thing audio has to a universal format, so you almost never have to think about compatibility.