[FEATURE/SPIKE] - Add option for VP9 video encoding via ffmpeg.

[bitbound]

I created a pipeline (https://github.com/bitbound/ffmpeg-minimal) for producing a small build of ffmpeg with the minimal amount of features necessary for encoding to VP9. Raw screen captures are piped in via stdin, and the encoded video is output to stdout.

I want to try adding an option to use with with remote control.

Similar experiments in the past have shown MediaSources API to be too slow due to buffering, so I'll try using VideoDecoder and drawing directly to a canvas.