How to Hide a Section of a Moving Object

[jimlolo]

I have an object in a layer that moves. I want to remove (cover up) the same section of that object. The object is always in the same orientation and size, it just moves up and down and left and right. I thought of using a mask, but I seem to have to move the individual nodes of the mask as the object moves in order to stay on the same section to be blockde.

is there an easier way to do this?

Thanks.

[Rick Gerard · Accepted solution]

The most efficient workflow depends entirely on the shot. You could use Mocha AE to track the region and create an animated mask on a solid layer to be used as a track matte. You could motion stabilize the shot with AE's feature tracker so that the object doesn't move, add shape layer or a solid with a mask and a null, then tie the stabilized layer's anchor point to the null's position property, go to the first frame of the comp and parent the mask layer and the motion stabilized footage to the mask layer to put the movement back in the shot and add it to the mask layer. You could use Mocha AE to corner pin track the object and then apply the Corner Pin data to a solid or shape layer you would use for the mask. There is even a way to motion stabilize a corner pin track so that it doesn't move with a combination of CC Power Pin, Corner Pin, and Mocha's AE tracker so the object stays exactly in one spot and remains the same size and shape so you can easily create a matte, then put the motion back in the mask. You might even be able to just use AE's Mask Tracking. 

If you can post a link to the shot, load it up in Dropbox or post it to YouTube, or at least embed a frame of the video with a description of the camera movement or the movement of the object we could give you some specifics. Embed images, create links of add YouTube or Vimeo videos using the toolbar on the forum.

[jimlolo]

so there is no way to move a shape or mask as a whole, instead of point by point? I could track, but it's not an easy 1. I'd be happy moving a shape by hand as things don't move much.

[Rick Gerard]

You can animate position, scale, rotation. You can tie one layer to another with parenting. That's why I said, show me the shot and I'll tell you the easiest way to do it.

It sounds like you need to spend some time with the User Guide.