Write a customized version of 'screengif'

[rein]

In short, suite this script to my usage: ffmpeg -i in.mov -s 600x400 -pix_fmt rgb24 -r 10 -f gif - | gifsicle --optimize=3 --delay=3 > out.gif

Reference:

1. https://gist.github.com/dergachev/4627207
2. https://github.com/dergachev/screengif (Ruby implementation)
3. https://trac.ffmpeg.org/wiki/Scaling (Would want something like -vf scale=iw/2:-1 to scale it down in half