References:
– conversion: http://xmodulo.com/convert-video-animated-gif-image-linux.html
– monitor: https://www.imagemagick.org/discourse-server/viewtopic.php?t=15860
– remove every-other: https://stackoverflow.com/a/12604488/5678759
Create a folder, and move the video file in to the folder.
At this point you have files. Viewing the folder should let you see the thumbnails. You can pre and post delete any files you grabbed by accident.
If the images come from an animation, you might want to delete every-other-file.
Next use ImageMagick to build the GIF.
I added `-monitor` myself to see what was happening. In my case it was freezing, hence the need to remove excess frames.
The original article then recommends using ImageMagick again for optimizing, but my file was too big.
Alternatively, gifsicle.