Use input as holdout / occlusion mask?

Hi there. Very new Mocha user here, probably the first of many dumb questions.

I’m using Davinci Resolve’s Fusion tab, which I believe is not officially supported but it seems to mostly work. I’m doing something similar to a phone screen replacement, and I want to hold out some fingers that cross the screen. Since I want some kind of mask / selection for the fingers for compositing purposes in Fusion, I was wondering if I could create that in Fusion, and also use it as a holdout when tracking in Mocha? I notice my Mocha node in Fusion has an input called “Source3” which has no purpose that’s immediately obvious to me. Probably a red herring but I’m curious as to what it’s for anyway.

Is there any way I can do this? Thanks.

What’s the process you want to use? Corner pins in Fusion or the Insert module? There’s many, many ways to do this and I want to make sure I am telling you the right one.

With holdouts in Mocha, keep in mind they need to be “outside” the object you’re holding out, looser is better to grab motion blur. But you can do tighter roto for the fingers for the final matte. Or you can do tight roto first, duplicate them, and then use Uber Key to bring the edges out to use them as holdout mattes. But you can’t import splines from Fusion. You could, however, simply export a black and white matte out of Fusion and use that as the holdouts. You just make a shape, go the matte clip, and import the mattes.

Sources for the plugin vary based on what you’re trying to do. I will tag @martinb though because I think we should probably label that.

Thanks Mary.

I’m using the insert module.

My idea is to do a “tight” roto / selection in Fusion and send a dilated version into Mocha for holdouts, somehow. It’ll be more like a key than roto, because I am lazy and it seems to work well enough, ie. bitmap not vector.

It sounds like maybe I can do what I want by exporting the mattes. Will have a look into that. But it’d be nice to be able to skip the export and pipe directly into Mocha, if there is any way to do that.


I am hearing a feature request we can poke @martinb about.

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Yes, we currently don’t have a way to pipe the mattes/roto from the host into Mocha, but you can import them directly from disk via the “Matte Clip” options in the Mocha GUI.
We have a feature request for this option to be included in the plugin itself, but more users requesting it will mean it’s more likely to happen!