Matroska / WebM file signature
Magic number at the start of the file
Matroska (MKV) and WebM share the EBML header 1A 45 DF A3. WebM is a strict subset of Matroska, so the outer bytes are identical; the DocType element inside (matroska or webm) distinguishes them.
What this magic number means
A magic number is a short, fixed run of bytes at a known position that tells a program what a file really is, no matter what the filename says. If a file starts with the bytes 1A 45 DF A3, it is a Matroska / WebM file.
Formats that use the 1A 45 DF A3 signature
These file types in our database carry this signature:
How to check a file's signature
You can read the first bytes of any file yourself. The magic bytes are shown in hex, the same way this page lists them.
Linux & macOS
- xxd -l 16 example.mkv
- hexdump -C -n 16 example.mkv
- file example.mkv
Windows (PowerShell)
- Format-Hex -Path example.mkv -Count 16
Python
- open("example.mkv","rb").read(4).hex()
In your browser
- Drop the file into the WhatFileType identifier, which reads the signature without uploading it.
Frequently asked questions
What is the Matroska / WebM file signature?
Matroska / WebM files start with the hex bytes 1A 45 DF A3. This magic number identifies the format regardless of the file's name or extension.
How do I check a file's magic number?
Open the file in a hex editor, or run a command such as xxd -l 16 example.mkv on Linux or macOS, or Format-Hex -Path example.mkv -Count 16 in Windows PowerShell, and read the first bytes.
Can a file fake the Matroska / WebM signature?
Renaming a file does not change its bytes, so the extension can lie but the signature usually cannot. A genuine Matroska / WebM file has these exact bytes; a file with the wrong bytes is not really Matroska / WebM, whatever its name says.