Scenecapture2d get pixel performance

hi guys~

my project use capture video card. the card’s api need pixel datas at every frame.
I use scence capture 2d get every frame, and use readpixels read the FColor.
Renderthread blocked by readpixels , so i use noblock readpixels. but it use my project drop fps.

i want to send rendertarget2d to another UE4 project to readpixel.
how to do?