Recording .webm

Hey,

Recently I’ve seen some videos here on facepunch where users posted .webm files, that were played automaticly, just as if it was an animated gif.
I’m wondering how to use this in Garry’s Mod, could anyone explain this to me, or did they convert it using third party software?

simply type gm_video in console

Thanks, and I think gm_video again to stop it?

yep