How can I cover sprocket holes in 8mm film?
 

I have some old 8mm film home movies which were recently digitized, and I now have them in ProRes 4444 format. They were overscanned on purpose (screenshot of a frame attached) so I know I have some cropping to do.

In addition to cropping, I'd really like to try and "cover up" the white sprocket holes with black so they are less distracting. (Is "mask" the appropriate term here?) Is this something I could do with AviSynth? If so, what function/plugin should I attempt this with? Or is there another application I would be better off using?

I realize I could just crop out the sprocket holes entirely, but if there's a reasonable way I could keep that extra portion of the image I'd really like to try.