What is WebM?
WebM is an open, royalty-free video container built on Matroska, holding VP8, VP9 or AV1 video with Vorbis or Opus audio. It was designed for the web and is what most browsers produce when a page records video.
WebM at a glance
- MIME type
- video/webm
- File extensions
- .webm
- Specification
- WebM Project container, a constrained subset of Matroska
- Compression
- VP9 and AV1 compress considerably better than H.264 at the same visible quality.
- Transparency
- Supported with VP8 and VP9 alpha channels, which is unusual and useful for web overlays.
- Animation
- Not applicable — it is video.
- Colour depth
- 8-bit for VP8, up to 12-bit with HDR for VP9 and AV1.
- Metadata
- Title, language and track tags. Less standardised than MP4 metadata.
- Support
- Native in Chrome, Firefox and Edge. Safari support depends on version and codec. Television sets, older phones and most video editors do not accept it.
Strengths and weaknesses
- Royalty-free, with no licensing questions for anyone shipping a player.
- VP9 and AV1 give a genuinely smaller file than H.264 at matched quality.
- Supports video with a transparent background, which MP4 in practice does not.
- Poor support outside browsers — do not send a WebM to someone by email.
- Encoding is slower than H.264, sometimes by a large factor.
- Screen recordings and downloads arrive as WebM and then refuse to open in normal editors.
Why you keep ending up with WebM files
Browser-based screen recorders, meeting tools and download extensions produce WebM because that is what the browser’s own recording interface emits. The file is perfectly valid; it simply belongs to the web rather than to the desktop.
Converting to MP4 with H.264 is the standard fix and is what makes the file open in a video editor, play on a television, or upload to a service that only accepts MP4.
Working with WebM files
Convert or edit a WebM file
- WEBM to MP4Convert WEBM video to MP4
- Compress VideoReduce video file size
- MP4 to MP3Extract audio as MP3
- MP4 to GIFTurn short clips into GIF
- Video TrimmerCut a section from a video
- Resize VideoChange video resolution
- Rotate VideoRotate or flip a video
- Mute VideoRemove audio from a video
- Adjust SpeedSpeed up or slow down video
- Reverse VideoPlay a video backwards
Formats people compare this with
- MP4MP4 is a container format, not a codec: it wraps video (usually H.264), audio (usually AAC) and metadata in one file, and it is the closest thing to a universally playable video file..
- MOVMOV is Apple’s QuickTime container — the format iPhones and Macs record into.
- GIFGIF is a lossless image format limited to a 256-colour palette per frame, with frame-based animation and one-bit transparency — obsolete for still images, still universal for short looping clips..