-Download and install AviSynth
-Download the "Plugin Package with all requirements" at the link above and carefully follow the instructions within on where to put the files. One of them has to go into your Windows system folders.
-Download v3.32 of the script from the above page.
Below is a test script to see if everything is working. I haven't tried multithreaded processing yet since I don't have Avisynth-MT installed.
AviSource( "x:\yourfile.avi" ) #Replace with your video file
AssumeTFF() #This line is important as AviSynth usually guesses field order incorrectly! Change to AssumeBFF() if working with bottom-field-first video.
QTGMC( Preset= "Slow" ) #Description of presets can be found on the avisynth wiki
SelectEven() #Needed to keep 29.97/25fps video. Remove if you want 59.94/50fps output