I'm not sure what codecs you need, but it does sound like FFDSHOW.

Brooks said:

This is feeling really complicated to me, is there no commercial program that can do this more simply? Is the ivtc really a dramatic improvement? :(

It restores the the video to it's original, progressive film format (from 29.97fps to 23.976fps). Depending on your final output, it can be a very big improvement...especially if you are resizing. It's hard to imagine converting anything from 4x3 to 16x9 without IVTC.

I don't know of any commercial programs, but there are many AviSynth filters at the AviSynth website that can do it automatically. Not sure which ones are best. I just have a habit of doing it manually.