Modification of WEBM/MP4 multi-core

FFMPEG, the tool being used by y'all, is already multi-core capable and the command output can be modified easily to use additional CPU cores.

I'm using a 16 core, 32 thread CPU, and waiting for a WEBM render is HORRIBLY LONG! I make modifications using Handbrake (a FFMPEG frontend) and can run a re-render in seconds!

https://twitch.tv/eireman