Follow instructions here: http://blog.fosketts.net/2010/08/09/assign-keyboard-shortcut-applescript-automator-service/

save_screencast_as_gif.scpt

set filePath to (path to desktop as text) & "screencast.mov"


tell application "QuickTime Player"
	activate
	set tdoc to new screen recording --> document "Screen Recording"
	delay 1
	tell application "System Events" to key code 49
	delay 2
	repeat while exists tdoc
		delay 1
	end repeat
	-- the recording is stopped
	open for access file filePath
	close access file filePath
	export (first document) in filePath using settings preset "1080p"
		delay 10
	close (first document) without saving
	quit
end tell

set user to do shell script "/bin/bash -c '/usr/local/bin/ffmpeg -i ~/Desktop/screencast.mov -pix_fmt rgb24 -r 10 -y -f gif ~/Desktop/screencast-`date +\"%Y-%m-%d_%H:%M\"`.gif'"