saveFrame() works, creates .tif's
ffmpeg command line did a good job with this:
ffmpeg -f image2 -i screen-%04d.tif -r 12 -s 640x360 CubicGridImmediate.avi
Windows Movie Maker seemed to have a limitation of shortest picture duration of 1/8 sec and transition of 1/4 sec so not really usable.
Thanks!