Parenting Masks to Null objects to inherit position data.
The reshape tool would become way more helpful with digital beauty work if AE had a way to parent Masks to a Null object that received tracking data from Mocha.
Ben Spear commented
Oh I just thought of a workaround by using a shape as an alpha matte. The shape can be Parented to a Null leaving you able to adjust the shape of the path and apply 'feather' with a blur filter. Hope that helps? It might mean creating a lot more layers rather than being able to apply multiple masks to one layer... Works a treat for what I needed!
Ben Spear commented
@Felix this is exactly what I am after doing. First time trying to Parent a mask to the Null I have applied my tracking data to... and can't quite believe it isn't possible straight out of the box :/
Nate Foster commented
Victoria, yes there is a way to do this in the Create Nulls from Paths panel, but it's rather cumbersome. you'd create a mask, then use Points Follow Nulls, then parent the created Nulls to a master PSR control null. It's a very clever method, but very limiting. you can't alter the vertex points of the mask at all after that. The curve of a bezier can't be altered, and that's an absolute necessity for Roto.
I think the OP is asking for and Felix elaborated on is a container for masks like the one for shape layers except easier to deal with. Adding in transform, scale, rotation, and Grouping to masks as are in Shape layers would be a good solution.
Felix Dames commented
Victoria, i think this feature request has nothing to do with the "Create Nulls from Path" panel/command. I think what is needed is an independent transform (anchor point, position, rotation, scale or a parent/link functionality) for the whole mask. Let's think of an moving object we need to rotoscope. We could easiely track position, rotation and scale (PRS Data) of that object in Mocha or AE's tracker. Now we apply that tracking data to a null layer in AE. The null moves and behaves nicely with the object to rotoscope. On the layer we want to rotoscope we now draw on the first frame to rotoscope our mask and parent it to our null layer either via a parent functionality or via expression or copy keyframes to/from the PRS tracking data of the null layer.
Now the mask moves nicely in a general sense with our object to rotoscope (but not the layer itself moves) and all we need to do is animate the mask for minor changes where the mask doesn't fit perfectly with the object to rotoscope. This results in very few needed keyframes for rotoscoping and it's a common practice in postproduction. This workflow is already possible in AE with an additional layer (e.g. a solid with the mask) linked to the null (RPS data) and used as trackmatte for the layer/object to rotoscope. But it requieres an additional layer mostly higher in resolution then comp size (depends on movement) and it clutteres up the comp and blocks the trackmatte usage for other purposes.
Can you give us a little more detail about how you'd like this to work? Some of what you're trying to do may already be possible -- take a look at the Create Nulls From Paths panel.