DVD playback normally keeps DVD's aspect ratio.
The only option available for DVD would be - Right-click, DVD Options, Crop Black Bars. It may not help, but try it anyway. ...
The "Crop black bars" option worked ...
EDIT: Oops!! ... crop black bars only zooms ... it does not change the aspect ratio! The DVD display is still squashed vertically.
Regarding display resolution options, I see nothing but 4:3 options offered. I wonder if MC isn't assuming my display is 4:3 from the native display resolution(?) The other mystery is that choosing different display aspect rations does nothing for DVD playback, while it does change for AVI playback. I have a feeling it's a filter option that I'm looking for, but there are so many ...
Let me emphasize again that AVIs play perfectly with MC, and I should also mention that the DVD player I've been using for years works also properly ... but I would like for MC to play
all my video files ...