Which filter will allow me to...

[Clydesdale]

crop black bars from left and right of screen?

[Manao]

Is that a joke ?

Anyway, the filter is called "crop", and works either by giving leftuppermost coordinate and width and height ( crop(x,y,width,height) ), either by giving the left margin, top margin, right margin and bottom margin in that way : crop(left,top,-right,-bottom)

You should really read the Avisynth documentation.