I use this command I found on SO (was the first Google result): https://video.stackexchange.com/a/28276 https://video.stackexchange.com/a/28276 ffmpeg -i

I use this command I found on SO (was the first Google result): https://video.stackexchange.com/a/28276 https://video.stackexchange.com/a/28276 ffmpeg -i input.mp4 -b:v 0 -crf 30 -pass 1 -an -f webm /dev/null ffmpeg -i input.mp4 -b:v 0 -crf 30 -pass 2 output.webm Making it two passes seems to be important for WEBM according to the post. It has worked well for me so far, but I need to look it up every time.