After Effect: Create Stroke from Motion Track Path
Select the motion keyframes &amp; copy. Now create a new mask on the layer on which you have the stroke effect, any old mask shape will do. Set its mode to none. Now select the mask's Mask Path property and paste. The mask can now be used to provide the path for the stroke effect (it's the first property in the stroke effect). You have to directly select the Mask Path property, just pasting it on the layer will paste it to the position property of the layer.



Because there's always more than one way of doing things in AE:

You can also create a shape layer with the pen tool. Once you've done expand the new shape layer until you see the Contents>Shape 1>Path property (it could be called Shape 2, 3 etc) and paste the motion path on to it. Then you can use it as a normal stroked shape layer.



Note As Alyssa points out below, when pasting a motion path to some other property you have to explicitly select that property, otherwise AE will just paste it on to the layer's position.