Understanding MP3 tags
ID3, and the metadata your music player reads.
How an MP3 file carries title, artist and album info, the difference between ID3v1 and ID3v2, and the album-art trick that's been the same since 1998.
ID3 in two flavours.
ID3 is the metadata format embedded inside MP3 files. ID3v1 (1996): a fixed 128- byte chunk at the end of the file with seven fields (title, artist, album, year, comment, genre, track number), each fixed-length and ASCII. Limited to 30 characters per field, no Unicode, no album art. ID3v2 (1998 onward): variable- length tag at the start of the file, supports arbitrary number of frames, Unicode, embedded images. Almost every file you'll meet uses ID3v2.
Frames are typed slots.
An ID3v2 tag is a header plus a list of frames. Each frame has a 4-character ID and a payload. TIT2 is title, TPE1 is lead artist, TALB is album, TRCK is track number, TYER (v2.3) or TDRC (v2.4) is year, APIC is attached picture (album art), COMM is comment, TCON is genre. The cryptic codes are stable across versions; tag editors translate them to friendly labels.
Album art is APIC.
The most common embedded image is the album cover, stored as an APIC frame carrying a JPEG or PNG plus a "picture type" byte (3 = "Cover (front)"). The image is embedded directly in every MP3 — every copy carries the same cover regardless of where the file lives. For an album of 12 tracks, that's the same image stored 12 times, which is wasteful but universally portable. Streaming services don't have this problem because they store the image once and serve it separately.
A worked edit.
A folder of 10 MP3 files freshly ripped from a CD, no metadata. The editor reads each file, presents an editable form (title, artist, album, track number, year, genre), saves the new ID3v2 tag back into each file. If the CD title was recognised by a service like MusicBrainz, the editor fills in everything from the database lookup; otherwise the user types it in once for the album and per-track for titles.
Bulk album tag
TALB, TPE1, TYER set across all tracks
Album-level fields the same per file; per-track fields differ.
TIT2 + TRCK per track ; TALB + TPE1 + TYER shared
= Library-ready files
Where tags hide bugs.
ID3v2 has version 2.3 (widely supported) and 2.4 (slightly newer features). Older software writes 2.3; modern software defaults to 2.3 for compatibility but may read 2.4. A file with both v1 and v2 tags is common; some players read one, some read the other, some merge. Encoding bugs cause mojibake (broken Unicode display) on players that misinterpret the byte order mark. Standardising your library on ID3v2.3 UTF-16 covers 99 % of cases.
Other formats, other tag systems.
ID3 is MP3-specific. FLAC uses Vorbis Comments (key=value pairs, simpler). M4A/AAC uses MP4 atoms (a hierarchical tree borrowed from QuickTime). OGG uses Vorbis Comments. WAV's INFO chunk is rarely used. Modern tag editors abstract over all of these and present a unified UI; under the hood each format has its own scheme. The conceptual model — typed fields, embedded images, per-file metadata — is the same; the wire format differs.