how to render a shadow but not the material?

so i’m trying to render out a looping animation of a guy walking with an alpha channel so i can composite it into a scene in after effects. the alpha channel works fine, but i want to render a shadow under him that has the same transparency. is there a way to put a plane under him and set it to only render the shadow and not the solid material that the shadow is cast upon? does this make sense? help!

Yes, select the plane and on the shaders tab in the materials buttons click the button labeled “Only Shad”.

Also, learn to use the nodes compositior. Once you get a handle on the nodes you won’t need After Effects for most of your compositing needs,mostly just for 2D effects. About six months ago someone posted saying that 90% of what most of us currently use after effects for would would no longer be necessary with the new render pipeline and nodes compositor and that just made me feel totally incredulous, but whoever that person was…they hit the nail on the head. Outsourcing to AE for composition work is becoming largely unnecessary in the new CVS builds.