Gajim is unrelated to Gaim. Gaim was renamed to Pidgin though, which still exists.
Draw a 2-pixel red 2.40:1 mask:
drawbox=x=-t:y=0.5*(ih-iw/2.4)-t:w=iw+t*2:h=iw/2.4+t*2:t=2:c=red
Implementing type checking on this correctly would require something like a DSL.