Glossary
What is WebM?
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WebM is an open, royalty-free video container format released by Google in 2010, designed for the web. It wraps video codecs (typically VP8, VP9, or AV1) and audio codecs (typically Opus or Vorbis). WebM is the default output of Chrome's tab capture and most browser-based screen recorders including Pullsy, and it plays natively in every modern browser without a codec install.
WebM is the right format for the screen but the wrong format for the rest of the world. QuickTime, iMovie, and Final Cut accept WebM only with plugin workarounds. Some social platforms and intranet tools still reject WebM uploads. The standard handoff is: record in WebM, then convert to MP4 (H.264 + AAC) before sharing outside the browser. The conversion is fast in ffmpeg.wasm and is exactly what Pullsy's webm-to-mp4 tool does, entirely in the browser with no upload. WebM is also a smaller file than MP4 for the same content at modern codec settings, which is why browsers default to it for screen capture — but the compatibility gap is the reason conversion matters. Related terms: screen recording, video transcript, screencast.