Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)
Standard-Def DVD provides for only two aspect ratios "natively": 4:3 and 16:9. Any other aspect ratio involves adding black bars to the edges of the encoded frame (letterbox or pillarbox).
That's assuming you want to generate standard DVD. Nothing prevents you from encoding a DVD with some other pixel aspect ratio (2:1, 2.4:1 etc while still using the full 720x480 NTSC frame), but it would look wrong (stretched or squeezed) on normal playback sets.