I had a need of this simple filter - there may be a better way to implement it, but the work's done now so I thought I may as well share it.
http://horman.net/simpleselect.zip
Code:
simpleselect(clip, f1 [,f2...,fn])
Return only frames f1, f2,...,fn of the source clip, e.g.
Code:
simpleselect(clip, 2, 3, 5, 7, 9, 13) # return a 6-frame clip comprising frames 2,3,5,7,9,13 of clip
David