When I capture from TV it's in 29.97 fps. Can I lower this to 21 fps to save space? I tried capturing at 21 fps but I got lots of dropped frames. I can capture at 20 fps but it looks choppy. Basically I just want the lowest file size without it looking slide-showish.

NTSC videocontains 29.97 frames per second. Short answer -- record at 29.97. Long answer --

Wow, my brain hurts after reading that. :)