SDI output Alpha

Development Rendering
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1

Hello,

I’m using media capture and I search how to send Alpha to SDI output ? Here are my settings :

alpha settings
alpha settings1229×243 10.9 KB

But my Alpha is totaly black. I have only one static mesh in the scene with light and post process. I turn the engine rendering project setting alpha to : “Allow through tone mapper”
Do I miss something ?

It is possible to see my alpha in viewport ? (other question)

Thanks for your help
JD