>>1555913https://cloudconvert.com/webm-converterWith the wrench button, choose none under audio/audio codec if you want it to work on 4chan outside of /gif/ and /wsg/. Webms with audio will get an upload not allowed message on the rest of 4chan.
Also pay attention to size as there are data size as there are size limits on 4chan too. /gif/ and /wsg/ have larger size limits.
BACK IN MY DAY, you had to make your own webms by installing/programming ffmpeg on your computer and learning a command line that worked for your shit.
But yeah, just use this site. And stick to what I mentioned above. You can use that site for a lot of shit.