What is webm?
An open, web-native video container - typically VP9 or AV1 video with Opus audio - built for smaller files on the open web.
WebM was built by Google specifically for royalty-free, efficient web video. It produces smaller files than MP4 at similar visual quality, which makes it a good choice for embedding video on your own site, but only a couple of social platforms (YouTube being the main one) accept it as a direct upload.
Converting a WebM to MP4 (or back) is a genuine re-encode, not a fast container swap - both are lossy formats, so keep the original source if you might need to convert again later.
Koldflux picks the right codec, container and bitrate for every platform automatically - this glossary exists because our own team had to get it right first.
Automate this in Koldflux