{
  "id": "magic/matroska-webm",
  "family": "magic",
  "slug": "matroska-webm",
  "title": "Matroska / WebM signature (EBML 1A 45 DF A3)",
  "summary": "Matroska (.mkv) and WebM files are EBML documents; they begin with the 4-byte EBML header magic 0x1A 0x45 0xDF 0xA3. The DocType element later in the header distinguishes 'matroska' from 'webm'.",
  "kind": "signature",
  "aliases": [
    "Matroska magic",
    "WebM magic",
    "EBML header",
    "MKV"
  ],
  "status": "standard",
  "verification": "verified",
  "tier": "C",
  "source_url": "https://www.rfc-editor.org/rfc/rfc8794#section-4.1",
  "source_version": "RFC 8794 (EBML), Section 4.1 EBML Header (EBML element ID 0x1A45DFA3)",
  "retrieved_date": "2026-05-29",
  "attribution": [
    {
      "claim_ref": "ext.magic_hex",
      "source_url": "https://www.rfc-editor.org/rfc/rfc8794#section-4.1",
      "source_version": "RFC 8794",
      "note": "Every EBML document starts with the EBML Header element whose ID is 0x1A45DFA3."
    },
    {
      "claim_ref": "ext.notes",
      "source_url": "https://www.matroska.org/technical/elements.html",
      "source_version": "retrieved 2026-05-29",
      "note": "DocType element ('matroska' vs 'webm') inside the EBML header distinguishes the two profiles; both share the 1A 45 DF A3 magic."
    }
  ],
  "see_also": [
    "magic/ogg",
    "magic/webp"
  ],
  "ext_type": "file-signature@1",
  "ext": {
    "magic_hex": "1A 45 DF A3",
    "offset": 0,
    "magic_ascii": "\\x1aE\\xdf\\xa3",
    "extensions": [
      "mkv",
      "mka",
      "mks",
      "webm"
    ],
    "mime": "video/x-matroska",
    "spec": "RFC 8794 (EBML) + Matroska/WebM specifications",
    "notes": [
      "1A 45 DF A3 is the EBML Header element ID, shared by all EBML documents (Matroska, WebM).",
      "The DocType child element holds the ASCII string 'matroska' or 'webm'; that is what tells them apart.",
      "WebM is a constrained Matroska profile (VP8/VP9/AV1 video, Vorbis/Opus audio)."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}