Auto/Video/Film Setting

[Outland]

I have an old SDTV with a BD player (Panasonic DMP-BD80) connected. I noticed that when I play DVDs on this player, sometimes there is a judder. However, if I set the "Progressive" option in the playback display menu from "Auto" to "Video," the judder goes away.

This setting is described here in the manual. What exactly does it control, and why does setting it to video make the judder go away?