ffmpeg: how to convert mov file to gif , and gif is resized [duplicate]

Question

how to use ffmpeg to convert mov file to gif , and gif is resized directly?

Here is the raw file

I firstly convert mov to gif,

ffmpeg -i input.mov -pix_fmt rgb24 output.gif,

then use imageMagick to resize the gif.

convert   output.gif -coalesce temporary.gif
convert -size 756x1504   temporary.gif -resize 189x376 smaller.gif

Here is the result:

How to use ffmpeg to do this directly, without using imagemagick