Recording simple GIFs for demos

Sometimes you might like to record little GIF animations of your screen to demonstrate an Emacs feature you did (hey, some of you might…). For example, these. I made a wee F9 keybinding for Emacs to run this:

(defun screenshot-frame ()
  "Take a screenshot of 400x200 pixels of the Emacs frame."
   (concat "sleep 1; "
           "import -window 0x3c000a3 "
           "-crop 400x200+13+0 +repage /tmp/frames/`date +%s`.png")))

Replace the window id with the window id of your target window, which you can get with xwininfo -display :0.

I would execute screenshot-frame after running a command or pressing a key (it sounds painful but it’s not, and it allows you to make mistakes). The sleep call is to ensure that the buffer has finished updating. I also disabled blink-cursor-mode. Then to preview the animation so far I would use

animate -delay 35 /tmp/frames/*.png

If some frames were redundant I’d remove them. And then finally to write out a .gif I’d use

convert -delay 35 /tmp/frames/*.png out.gif

I found the whole thing quite convenient!