.webm — WebM Video
Video video/webm
What a .webm file is
An open, royalty-free container for VP8/VP9 or AV1 video with Vorbis or Opus audio, designed for HTML5 video.
How to open it
All current browsers, VLC, MPV.
Worth knowing
Smaller than MP4 at equivalent quality, but Safari support arrived late and some older devices still struggle.