visualise.sh doesn't work with older players and VLC

[liamdalg]

The visualise.sh script won't work with Windows Media Player and other old players, and also won't work with VLC due to a bug with playing low framerate videos.

These two stackoverflow answers have some information about them:

https://stackoverflow.com/a/44033863 for Windows/older players (should only need pix_fmt option)
https://stackoverflow.com/a/41797724 for VLC

I think we need to have something like:

ffmpeg -framerate 3 -r 30 -pix_fmt yuv420p -i out/%010d.png output.mp4

Will need to fix the visualise.sh script and redo the example videos.

[liamdalg]

We should sort this out soon, people keep complaining about it

[liamdalg]

https://gist.github.com/Vestride/278e13915894821e1d6f this might work as well (and be less weird about video size)