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Capture Component Output with Alpha

I’m trying to output video from a UE4 capture component to another application, with alpha transparency instead of a skybox, during runtime.

Does UE4 have a built in means of this I just haven’t found yet?

With the Newtek NDI plug-in, an alpha mask is applied over each actor, as the top layer of the scene, omitting any post processing that would have normally been rendered on top of the actor.

If I could selectively choose which actors to mask and apply the alpha layer behind the post-processing effects, I could achieve my goal with a masked wall placed behind my scene and other actors rendered normally. These options aren’t built into the plug-in, but the SDK is open-source.

Can I affect the render pipeline to layer post processing over the alpha mask?

Here’s a gif of the closest I’ve gotten to success so far. The post processing effects were mostly lost unless seen between the camera and the three objects being rendered. The black & white background image is not part of the scene. Screen capture - 69095632eff3589fc2611a7a7847f159 - Gyazo