[MrJ]

Originally Posted by Gavino

Use ScriptClip() to crop at a per-frame varying position.

Thanks Gavino.
I was trying to avoid sounding like a total avisynth noob but, gulp here goes..

LoadPlugin("C:\...DGDecode.dll")
vid=mpeg2source("F:\....d2v")
#As is no doubt obvious I'm not sure of the syntax for this. It needs a vid and more
ScriptClip("""
    x = current_frame   #variable
    a = 2.9017E-08      #constants
    b = 2.41882E-03
    c = -2.47594795
    
    pdown = a*x^2+b*x+c    #number of pixels to crop from the top of the 1080 frame
    pd=Round(pdown)        #whole number of pixels to crop from the top of the 1080 frame
    
    pup = 360-pd           #whole number of pixels to crop from the bottom of the 1080 frame
    
Crop(320, pd, -320, -pup)
""")

I'm posting this not because I think it's anywhere near right but to try and clarify what I'm trying to do. Any pointers gratefully received.