[vampiredom]

I think I found a better approach to this, using something more like stickboy's suggestion. When input is YV12, the function converts to YUY2. When input is YUY2 it converts back to YV12.

function TogglePlanar(clip c) {
	c
	wasYV12 = isYV12()

	y = ConvertToYUY2()
	u = UtoY()
	u = Interleave(u,u).AssumeFieldBased().Weave().ConvertToYUY2()
	v = VtoY()
	v = Interleave(v,v).AssumeFieldBased().Weave().ConvertToYUY2()
	
	(wasYV12) ? YToUV(u,v,y) : c.ConvertToYV12()
	(GetParity(c)) ? AssumeTFF() : AssumeBFF()
}

So, in my case of GrapeSmoother (though it could be any YUY2-only filter)...

# usage example:

(isYV12) ? TogglePlanar().GrapeSmoother(30).TogglePlanar()
       \ : GrapeSmoother(30)

I was surprised to see that Interleave(v,v).AssumeFieldBased().Weave() was a tiny bit faster than PointResize() ?? Thanks!