Post record optimisation

From personal experience it's a tall ask to record in one step on low performance computers.
Suggest add option to post-optimise the original _'uncompressed'_ file recorded
Here is what is used (...before finding ffscreencast)
- i record in as efficient a format as I could find for low performance cpu AND _drive. _i could be wrong about libx264 and rgb24 usage._
- i also record only 640x480/vga/sntsc at 20 fps then reduce to 10
- 18MB -> 1.1MB
- libopus support for mono 16-20 kbps is very efficient for voiceovers
- i've also been looking for a way to record 'faked' mouseclick sounds and keypresses into a channel so it's not using the microphone to record the typing. could use same solution to show modifier and function keys pressed on overlay **see** `https://github.com/wavexx/screenkey`

**#my 60 second test record**
ffmpeg -f x11grab -framerate 20 -video_size 640X480 -i :0.0 -c:v libx264rgb -pix_fmt rgb24 -tune animation -crf 0 -preset ultrafast -t 60 raw.mp4
## one minute is about 16mb

**#my_ re-compress, _oddly_ -crf 35 still looks good.**
ffmpeg -i raw.mp4 -c:v libx264rgb -r 10 -preset veryslow -crf 35 -tune animation -movflags faststart compressed.mp4