Black Bars Filming Technique

Saw an image where someone was able to get black bars above and below the glitch for filming, does anyone know how to achieve this?

Use a mixer with a top-and-bottom-to-center wipe and only wipe it 1/3 of the way?


I ended up finding a triniton and it has this “16:9 enhanced” feature, so I can pump all my video through my crt in 16:9 on a flat screen it works out really well for rescanning