Theory & Basic Methods of Using Mocha?

Hi Everybody,

I’m new (again) to Mocha AE after attempting to learn it a year or so ago. I’m finding that practice really makes perfect in terms of selecting useful points to track and getting results to keep it from slipping. I don’t mind spending the time but I have to admit I don’t really understand what it is that I’m doing. All these tutorials teach you what to do but I don’t ever hear the theory behind each basic tool, why I’m doing what I’m doing, and how they relate to each other.

A) For instance the Spline Layer tool. I’m making a “garbage matte” loosely around the object in question and it just “works”?

B) Adding X-Spline to layer? How does that relate to the first spline and why am I doing what feels like the same thing twice?

C) Surface? How does that differ from the X-Spline points I just put down?

I read the manual section for this and I’m manipulating these tools but I kind of feel like I’m not quite understanding the relationship of these tools.

Could somebody clarify on what is actually happening with these steps other than “connecting the dots”? I really like this tool but I constantly forget how it works because I don’t understand the theory behind my manipulations of these tools.

Thanks a bunch for reading and any suggestions to clarify Mocha.


A) When you are tracking an object, the spline is creating a mask to define the search area. It can actually be helpful for the tracker to see part of the background, so it is better to draw outside the object, rather than exactly around it. You have to of course give mocha something it can track. If you try to track a surface with no texture details or is turbulent like ocean waves, you are going to run into problems.

B) “Add X-Spline to layer” is to give you additional splines to track or roto with on the same layer. Imagine a scenario where you are tracking a building, and the spline you are tracking with goes off screen. Rather than move the original spline to capture more of the building on screen or start a different track, you can add more splines to keep that search area going. You can use as many different search areas as you like in a single layer. Adding a spline also lets you cut a hole out of an existing spline by drawing over the top of it. This is especially useful when dealing with screens that have reflections, because you can cut a hole to avoid the reflection.

C) The surface is the representation of the actual tracking data. Since we track with planar data, the surface is the best way to represent that plane. You can modify the fit of the surface and it is a child object of the tracking data.

I highly recommend watching this video for more info on how the surface works in relation to the spline: Boris FX | Quick Shots: What lies beneath the Surface