DGindex shows that it is simply NTSC and interlaced. I didn't select forced film, and left the framerate at 29fps. Later, when I was to start encoding, I selected Field Deinterlace and I checked "Correct framecount." The resulting rip isn't interlaced and looks okay, but is 29fps! I've tried uninstalling and reinstalling gknot and various codecs, but the rip has never had a framerate of 23fps.

I know movies shot a certain way are okay to leave at this, but it really seems odd that it won't change. When is it alright to leave at this framerate?

No idea how to tell if a film is pure NTSC and should be left at 29fps but if you had checked IVTC instead of Field Deinterlace it would have converted it to 23.976fps.

I thought you're not supposed to do that with interlaced material?

From "Spud's Ripping Tips V0.1"

I thought that myself and checked with Dxa who told me to ignore the warning in GK. IVTC and forced film both deinterlace although I have had problems with some NTSC DVD's, it's really a matter of trial and error. Better still the USA and Japan should get their act together and use PAL like everyone else

I'm no expert but if you read thru this post
http://forum.dead-donkey.com/viewtopic.php?t=8714
I did exactly the same and it was left in the HQ so i guess it was ok

they are extremely rare where you can leave in @ 30fps.

Have you manually checked the frames... this is the best (well only) way?

if you have a sequence of Progressive and interlaced frames then it needs ivtc, if they are all interlaced, then its like to be 30fps. If there's more than one identical frame or a sequence of p and i frames it needs ivtcing.

If you advance a frame at a time in gknot in the preview window it very rapidly becomes clear if it needs ivtc'ing or not. I reiterate, its extremely rare with a retail source these days to ever find one at pure ntsc.

Sometimes its tricky, you should always watch your rips for a while to see if a) the playback is jerky b) there's any ghosting c) there's any mistakes

Technically you should IVTC some pal rips to 24fps, but its hard to find when to do them.

Dr Phibes, there's some rips in higher quality that should be moved and haven't, and i'll admit there's probably some been moved that shouldn't have. Its very hard to see what to do from afar. I don't know if i have that rip to check, but you need to ask yourself whether you consider the source and rip 'high quality' as well. In my experience if its 30fps the film normally looks like ass anyway because its been filmed on a home camera rather than a cinema camera If you want to check the movie, go through and look for duplicate frames in virtual dub by progressing a frame at a time.