What is the WEBM file format?
A .webm file contains multimedia data as a Matroska-derived container - a constrained subset of the .MKV format designed for open web delivery. The format was developed with support from Google in 2010 as a free, open format for internet-related purposes. A .webm container can comprise:
- video stream data encoded in VP8, VP9, or AV1 technology,
- audio stream data compressed using the Opus or Vorbis codec,
- text tracks in WebVTT format - the initial version of the format did not support any type of subtitles.
The format is restricted to only selected codecs, all of which are open-source to facilitate use in free and paid applications. Web browsers that support WebM should have no problem opening any .webm file, as no additional codecs need to be installed on the system. The format is well-suited for streaming of variable quality and adaptive bitrate delivery. .webm is also commonly used for videoconferencing.
No additional software is required to use this format, as any application that supports it already has the necessary resources to process .webm data. When a file stores audio and video, its MIME type is video/webm; for audio-only content, the MIME type is audio/webm. .webm shares its binary header magic (1A 45 DF A3) with .MKV files and is distinguished internally by a DocType element. Related open formats include .OGG for audio and .MP4 for wider codec support.
Security & safety
RISK: LOWA WebM file contains media data, not executable code, so the file itself is low risk. Real-world dangers are adjacent: fake 'WebM codec packs' or 'WebM player' downloads that bundle adware (you never need one - VLC and browsers play WebM natively), .webm.exe double-extension tricks, and online converters that upload your private video to a third-party server. Use a local tool (VLC/HandBrake/ffmpeg) for anything private and keep players updated.
Format details
in a nutshellPrograms that open WEBM files
Windows4 apps
VLC media player
Open-source Right-click the .webm → Open with → VLC. Plays VP8/VP9/AV1 + Vorbis/Opus with built-in codecs. 
Any web browser (Chrome, Firefox, Edge)
Free Drag the .webm into a browser tab - WebM is a native web format and plays instantly. Quick way to view without installing anything.
Media Player (Windows 11) / Movies & TV
Built-in Double-click to play; Windows 10/11 supports WebM (install 'VP9 Video Extensions' / 'Web Media Extensions' from the Store if a codec is missing). 
macOS2 apps
VLC media player
Open-source Drag the .webm onto VLC - QuickTime Player has limited WebM support, so VLC is the reliable choice.
IINA
Open-source Modern native macOS player (built on mpv) that handles WebM; set as default for .webm in Finder. 
Linux2 apps
Android1 app
VLC for Android
Open-source Open from a file manager; Android also plays WebM natively in most galleries/browsers.
VLC for iOS
Open-source Add the file via Files/AirDrop and play in VLC; iOS's built-in player has limited WebM support.
CloudConvert
Freemium Upload the .webm to convert it to MP4 in-browser; convenient for one-off small files (uploads to a third party - avoid for private video). Technical details
deep spec| Container base | EBML (Extensible Binary Meta Language) - a constrained Matroska subset optimised for open web delivery |
| Supported video codecs | VP8, VP9, and AV1 |
| Supported audio codecs | Opus and Vorbis |
| Subtitle format | WebVTT (Web Video Text Tracks) |
| MIME type | video/webm (audio + video); audio/webm (audio only) |
| Magic bytes | 1A 45 DF A3 at offset 0 (EBML header; shared with MKV, distinguished by DocType “webm”) |
| DocType identifier | “webm” stored in the EBML DocType element, distinguishing it from Matroska’s “matroska” |
| Native browser support | Chrome, Firefox, Edge, and Opera play .webm natively without plugins or extra codec packs |
| Adaptive streaming | Compatible with MPEG-DASH for adaptive bitrate delivery over HTTP |
| Maximum resolution | No hard container limit; VP9 and AV1 support up to 8K (7680×4320) in practice |
| HDR support | VP9 Profile 2 and AV1 support 10-bit and 12-bit colour depth for HDR content (BT.2020 colour space) |
| Alpha channel video | VP8 and VP9 support a dedicated alpha plane for transparent video layers |
| Multi-track support | A single .webm file can contain multiple video, audio, and subtitle tracks |
| Random-access seeking | Block-accurate seeking enabled by EBML Cues index elements embedded in the container |
| Encoding toolchain | ffmpeg supports .webm output via -c:v libvpx-vp9 (or libaom-av1) and -c:a libopus |
| Colour primaries | VP9 and AV1 signal BT.709, BT.2020, and DCI-P3 colour primaries for SDR and wide-gamut content |
| Released | 2010 (Google, royalty-free web video) |
| Open standard | Yes · royalty-free |
| Specification | www.webmproject.org |
WEBM conversions
Community Q&A
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