What is a .webm file and how do I open it?

WebM is an open, royalty-free video format built for the web. It uses efficient VP9 or AV1 video and plays directly in modern browsers, which makes it common for background videos and HTML5 players.

What is a .webm file used for?

WebM is a trimmed-down cousin of Matroska aimed squarely at the web. It pairs VP8, VP9 or AV1 video with Vorbis or Opus audio, all free of licensing fees.

Browsers play WebM natively, so it is a favourite for embedded and background video where you want small files and no plugins.

Outside the browser, support is thinner, so for editing or sharing you may convert a WebM to MP4.

What opens a .webm file?

The .webm format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list.

Windows

VLC
any browser

macOS

VLC
Chrome, Firefox

Linux

VLC
mpv
any browser

Web

Most modern browsers

Open a .webm file step by step

Confirm the file really is a .webm. Drop it into the WhatFileType identifier, which reads its signature in your browser without uploading anything.
On Windows, open it with VLC or any browser.
On Mac, use VLC or Chrome, Firefox.
On Linux, try VLC or mpv.
Still stuck? Convert the .webm to MP4, which opens more widely.

Why can't I open my .webm file?

Almost always because no installed app understands WebM. Install one of the apps above, or convert the file to a format your existing software already reads. If double-clicking opens the wrong program instead of nothing at all, the file association is set to the wrong app rather than the file being broken.

The other possibility is that the file is not really a .webm at all. Drop it into the file identifier to check it by its bytes instead of its name. Nothing is uploaded.

How to convert a .webm file

You can convert a .webm file to MP4, GIF, MOV using a conversion tool or the export menu of an app that opens it.

What is the .webm file signature (magic bytes)?

A .webm file starts with the hex bytes 1A 45 DF A3. Programs identify WebM by those bytes, not by the filename, so a renamed file still gives itself away.

These are the documented signatures for WebM. For a full breakdown, see the Matroska / WebM file signature page.

Documented magic-byte signatures for the .webm format
Hex signature	Offset	ASCII	Note
1A 45 DF A3	0	-	EBML header (shared with MKV)

See the full magic-numbers reference for every format.

Frequently asked questions