Wii Video 9 (nice title) didn’t want to work for me, so here’s a better way with ffmpeg:
ffmpeg -i "gatogrande.mp4" -vf scale=-1:480 -c:v mjpeg gatogrande.avi
Videos don’t have sound, not sure which one I need to use, as it seems the default AAC codec ffmpeg uses does not work. Might update this post if I find out.
In any case, I’m happy to have finally got this elusive (to me anyway) feature to work: even the puzzle game works, and you can post frames to the Message Board and Wii Menu banner. The Photo Channel’s a lovely piece of kit, really. Good memories with it.