This is (yet another) port of a filter by Donal Graft. It removes frames according to several strategies. The most common usage is with telecide to do inverse telecine.
By default it was transform 29.97(nbsp)fps (or 30(nbsp)fps) video to 23.976(nbsp)fps (or 24(nbsp)fps). This should only be done if you WANT to have 24 fps video output, like with PAL video, but NOT for NTSC.