{
  "id": "magic/mp3-id3",
  "family": "magic",
  "slug": "mp3-id3",
  "title": "MP3 / ID3 signature (ID3 or FF Fx frame sync)",
  "summary": "An MP3 file most often begins with an ID3v2 tag whose first three bytes are the ASCII 'ID3' (0x49 0x44 0x33). A bare MPEG audio stream instead begins with an 11-bit frame sync: 0xFF followed by a byte whose top 3 bits are set (0xE0 mask), commonly seen as FF FB / FF F3 / FF F2.",
  "kind": "signature",
  "aliases": [
    "MP3 magic",
    "ID3",
    "ID3v2",
    "MPEG frame sync"
  ],
  "status": "de-facto",
  "verification": "verified",
  "tier": "C",
  "source_url": "https://id3.org/id3v2.4.0-structure",
  "source_version": "ID3v2.4.0 structure (tag identifier 'ID3'); MPEG frame sync per ISO/IEC 11172-3",
  "retrieved_date": "2026-05-29",
  "attribution": [
    {
      "claim_ref": "ext.magic_hex",
      "source_url": "https://id3.org/id3v2.4.0-structure",
      "source_version": "retrieved 2026-05-29",
      "note": "ID3v2 tag begins with the file identifier 'ID3' (49 44 33) followed by two version bytes and flags."
    },
    {
      "claim_ref": "ext.notes",
      "source_url": "https://en.wikipedia.org/wiki/MP3#File_structure",
      "source_version": "retrieved 2026-05-29",
      "note": "Corroborates that MPEG audio frames begin with an 11-bit sync (FF Ex/Fx); ID3v2 tags commonly prefix MP3 files, ID3v1 trails them."
    }
  ],
  "see_also": [
    "magic/flac",
    "magic/ogg"
  ],
  "ext_type": "file-signature@1",
  "ext": {
    "magic_hex": "49 44 33",
    "offset": 0,
    "magic_ascii": "ID3",
    "extensions": [
      "mp3"
    ],
    "mime": "audio/mpeg",
    "notes": [
      "Tagged file: starts 'ID3' (49 44 33) — an ID3v2 header — then the audio frames follow after the tag.",
      "Untagged file: starts with an MPEG frame sync, 0xFF then a byte masked 0xE0, e.g. FF FB (MPEG-1 Layer III), FF F3 / FF F2 (MPEG-2/2.5 Layer III).",
      "ID3v1 metadata, if present, is a fixed 128-byte block at the END of the file starting with the ASCII 'TAG' (54 41 47).",
      "Because the audio is frame-based, detection by frame sync can have false positives; the ID3 prefix is the reliable signal when present."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}