Yesterday I needed to convert a video screen recording I made to a GIF in order to upload to Github. I discovered that this can be done quickly and easily with a terminal tool called ffmpeg. Here's how you do it:
brew install ffmpeg
brew install gifsicle
ffmpeg -i Screen\ Recording\ 2020-09-11\ at\ 19.36.10.mov -s 1440x900 -pix_fmt rgb24 -r 10 -f gif - | gifsicle --optimize=3 --delay=3 > screen-recording.gif
Screen\ Recording\ 2020-09-11\ at\ 19.36.10.mov with the path to the video file and
screen-recording.gif with the path to the GIF you want to create.
Hope this helps someone :)