Looking to blur objects in a scene but do not want to use the circle blur that comes with FCP. Is there another blur option for specific shapes, something similar to a rectangle?
Use one of the Matte options to isolate whatever you want, then apply the blur filter to the layer you want blurred. I recently did the reverse of what you describe -- isolate a certain region and blur everything else -- and it was a relatively complex shape, and it had to move ... matte made it a piece of cake.
