What is a WebM file?
WebM — royalty-free web video
What is it?
WebM is a video format designed exclusively for the web: lightweight, royalty-free, and playable directly in the browser without an external player.
It's a stripped-down version of the Matroska container, deliberately limited to a handful of open codecs — VP8, VP9 or AV1 for video, Vorbis or Opus for audio.
History & origin
Google released WebM in 2010, after acquiring the company behind the VP8 codec, and made it entirely free of licensing fees.
The goal was clear: give the web an alternative to H.264, which was then covered by a patent pool demanding licensing payments. This effort directly paved the way, a few years later, to AV1.
Why it is useful
Very light files at equal quality, native playback in every browser, and no royalties to pay.
It supports video transparency, which MP4 doesn't — useful for overlaying an animation on a page.
Limits & drawbacks
Outside the browser, compatibility falls apart: TVs, set-top players and editing software often don't support it.
Encoding in VP9 or AV1 is much slower than in H.264.
Practical tips
WebM is the right choice for video embedded in a web page. For emailing a file or playing it on a TV, convert it to MP4 first.
On a website, serving both formats — WebM for modern browsers, MP4 as a fallback — remains the safest strategy.
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