The short answer

The name is usually read as “MP3 URL”. The format was developed by Fraunhofer for its WinPlay3 software, and many players adopted it later; its origin is not formally documented. There is no formal specification either. An M3U file is a text file with the extension .m3u, and .m3u8 is the same format saved as UTF-8. Either one can be opened in any text editor.

What is inside

A basic file has two kinds of lines:

  • An optional header, #EXTM3U, which marks the file as extended.
  • Entries: a path or address on its own line, often preceded by an #EXTINF line giving a title and a duration.

Lines that begin with # are tags or comments. A player reads the lines that it understands and skips the rest.

What it does not contain

An M3U file does not hold audio, video or image data. It holds only the locations of those things. If a location is wrong, moved or offline, the list still opens but the entry will not play.

Who uses it

Music players, media servers and some streaming applications read M3U files to build a queue. Developers also write them when they need a simple, editable list that any tool can produce.

Next steps

To see every line of a file, use the M3U File Inspector. For a line-by-line walk through an example, read anatomy of an M3U file. If you need to know which extension to use, read M3U vs M3U8.