Intermediate problem: how to capture the on-screen action. I needed some form of screencam software to do that.
Intermediate answer: XVidCap!
XVidCap isn't available in the Ubuntu repositories, but it's okay. You can download a
.debfile from SourceForge.
Once you get that, installation is simple:
sudo dpkg -i xvidcap_1.1.5rc1_i386.deb
A menu item for XVidCap should now appear in the
Sound and Videogroup of your
Applicationsmenu. You can also invoke it manually with
Launching XVidCap brings up a floating menu bar with buttons to select capture windows and to start and stop recording. Files are saved in MPEG, suitable for uploading to Google Video or YouTube.