vidpickr

Glossary · format

What is WebM?

WebM is an open container format developed by Google for the web. It pairs VP9 or AV1 video with Opus or Vorbis audio, all royalty-free. WebM files play natively in every modern browser and are common on YouTube, Wikipedia, and OBS recording outputs.

Also called:.webm · web media

WebM is a deliberately constrained subset of Matroska (.mkv) — same fundamental design, narrower codec choices. The narrowness is the point: every WebM file is guaranteed to play in any modern browser without plugins. There are no "this file won't play" surprises like there sometimes are with MKV.

YouTube serves a WebM version of every popular video alongside the MP4 version. Browsers that prefer VP9/AV1 (Chrome, Firefox, modern Edge) get WebM; older Safari and various TVs get MP4/H.264.

For downloading: pick MP4 if you need universal device support, pick WebM if you want the smallest file for the same quality and your destination supports it.

Common questions

Will WebM play on my iPhone?
Native iOS Safari support arrived in iOS 14.5. Older versions and many third-party iOS apps don't accept WebM. Pick MP4 for older iOS targets.

Related terms

MKV (Matroska)

MKV (Matroska) is an open, flexible container format that holds video, audio, subtitles, chapters, and metadata in a single file.

Container (file format)

A container is the file format that wraps one or more audio and video streams into a single file.

VP9

VP9 is a royalty-free video codec developed by Google, used widely on YouTube and in WebM files.

AV1

AV1 is a royalty-free, open-source video codec from the Alliance for Open Media.

VidPickr is a free, browser-based YouTube downloader. Every term in this glossary either describes how YouTube delivers video or why your downloads behave the way they do. Try the downloader →