The Smith Chart video will be relatively short, they are fairly simple and very handy.
Hmmm - well, if I want to explain what each of the 7 scales of the chart are, plus the 10 or 11 radially scaled axis - that would be a decent length video itself. Then, explaining how to plot complex values, how they "move" with frequency or added transmission lines - another decent length video. Of course, then we should talk about impedance matching, using lumped elements and stubs - that's a few more videos... I've been trying to mentally parse the list of topics to start formulating my videos...