Title, Artist, Album Artist, Composer: which MP3 tag field does what

An MP3 tag is a small form stapled to the front of the file: Title, Artist, Album and a handful more. Your player reads the form and files the song. Most of the fields do what the label says. Two of them, Album Artist and Composer, take a moment to understand, and between them they caused most of the mess in my own library before I worked out what they were for.

Where the fields live

The tag is a block of data called ID3, and nearly every tagger writes version 2.3 of it by default. Inside that block each field is a "frame" with a four-letter ID. You never type these yourself, but desktop taggers show them, so here's the lot.

There's also an older tag, ID3v1, which is 128 bytes bolted onto the end of the file. It has room for Title, Artist, Album, Year, Comment, Track and a one-byte genre code, and every text field is chopped at 30 characters (28 for the comment when a track number is stored). No Album Artist, no art. If you've ever seen a title cut off mid-word, that's ID3v1. What's inside an MP3 tag shows what both versions look like in the raw bytes.

Title, Artist and Album

Title is the name of this one track. Artist is who performs it. Album is the release it came from. Most of the time that's all the thinking required.

The traps are about consistency, not meaning. "The Beatles" and "Beatles" are two artists to your player. "Abbey Road" and "Abbey Road (Remastered)" are two albums. A trailing space nobody can see makes a third. When an album shows up in pieces it's nearly always one of these or the Album Artist problem below; the fixes are in why an album splits into several.

Album Artist, the field everyone skips

Here's the situation. You've got a film soundtrack with fifteen tracks by fifteen different bands. Artist is correct on every one. You open your phone's music app and instead of one album you have fifteen, each holding a single track, all with the same name.

That's the Artist field doing exactly what it was told. The player groups by artist first and album second, so fifteen artists means fifteen groups. The same thing happens on an ordinary album when track 7 is "Someone feat. Somebody Else". That one track wanders off on its own.

Album Artist answers a different question. Not "who performs this track" but "whose album is this". On a compilation you set it to "Various Artists" on every track. On an album with a guest on one song you set it to the main act. Apple Music, iTunes, Windows Media Player and most phone players group by Album Artist when it's present and only fall back to Artist when it isn't. Fill it in and the fifteen little albums snap back into one.

I set it on everything now, even solo albums where it just repeats the Artist. It costs nothing, and it means the grouping never depends on a guess.

Composer is not a spare Artist field

For pop music Composer sits empty and nobody minds. For classical and film music it's the whole point. Artist is who performed the recording: the orchestra, the conductor, the pianist. Composer is who wrote the notes.

Put "Beethoven" in Artist and you've built a large pile of tracks by one performer who hasn't been in a studio for some time. Put the orchestra in Artist and Beethoven in Composer and both questions get a correct answer. Film scores work the same way: orchestra in Artist, composer in Composer.

Track and disc numbers

Track number puts songs in album order. Leave it out and the player has to guess an order from the title or filename, which is rarely the one on the sleeve. You can write it as 3 or as 3/12, position and total. The total is optional. I fill it in because it makes a half-copied album obvious: nine files, all saying /12.

Disc number does the same job for multi-disc sets and takes the same form, 1/2. Skip it and disc two's track 1 can land right next to disc one's track 1, so a double album plays as interleaved pairs. Set it and the discs line up.

Year, Genre and Comment

Year is the release year. ID3v2.3 stores it in a plain frame called TYER; ID3v2.4 replaced that with a recording date, TDRC. Players mostly use it to sort an artist's albums into order, and a bare year is enough for that.

Genre is free text in ID3v2. "Rock", "Folk", "Songs for the car", anything you like. The old ID3v1 tag stored it as a single byte from a fixed list, which is why some taggers still offer a dropdown of those names; the full list is in the ID3v1 genre list. Pick something you'd actually filter by. I've been through three schemes and settled on about a dozen genres, because a hundred genres is the same as none.

Comment is a notebook. Where the file came from, that the rip has a click at 2:14, that this is the good live version. Players rarely show it and nothing groups by it, so it's the one field you can't break anything with.

Cover art

The picture lives inside the file too, in an APIC frame, so it travels with the MP3 wherever you copy it. Some players pick up a folder.jpg sitting next to the files; every player that shows art at all reads the embedded one. One square image per file is plenty. It has to look right at the size of a stamp on a phone screen, not on a poster.

Which fields actually matter

My opinion, after years of tidying: Title, Artist, Album, Album Artist, Track number and cover art. Those six are what a player uses to build the screen you look at. Get them right on every file and the library looks finished.

Year and Genre are nice. Disc number matters only if you own multi-disc sets. Composer matters if you listen to classical or scores and can otherwise stay empty. Comment, Lyrics, BPM and Key are for people who already know they want them.

What the editor here does and doesn't write

The editor on this site writes Title, Artist, Album, Year, Track, Genre, Comment and cover art. It has no fields for Album Artist, Composer, Disc number, Lyrics, BPM or Key.

That's deliberate. It's built for the quick fix: a wrong title, a missing cover, a folder of files with no tags at all. For a compilation that needs "Various Artists" on every track, or a box set that needs disc numbers, use a desktop tagger. Mp3tag (Windows and macOS) and Kid3 (Windows, macOS and Linux) are both free, and both have the fields this one doesn't.