Format overview
What is WebM?
WebM is a Matroska-derived container designed for royalty-free web media. Common combinations include VP8 or VP9 video with Vorbis or Opus audio; current workflows may also use AV1.
WebM can support alpha transparency with compatible VP8 or VP9 encoding, making it useful for overlays and web animation as well as ordinary video.
Compatibility
Browser and device compatibility
Current browsers support common WebM combinations, but exact codec and alpha support varies. Some editing applications, televisions, and Apple-oriented delivery systems prefer MP4 or MOV.
A .webm extension does not guarantee that every browser can decode the contained AV1, VP9, or audio profile, so test the actual output on each target platform.
Practical use
When should you convert WebM?
Keep WebM for compatible web delivery, especially when VP9, AV1, Opus, or transparency is required. Convert to H.264 MP4 for broader device and application support, or to an editing profile before timeline work.
For websites, provide formats that match the browser audience and use HTML video source fallbacks when one codec cannot cover every target.