What exactly are you trying to do? Make the billboard out of focus? Since the video doesn’t contain any depth information, wouldn’t it be easier using the Blurrer module?

Hello, 

The billboard is not affected by the depth of field effect due to limitations in the Unreal Engine.

Translucent objects - like the billboard - are rendered after the DOF blur is applied to the scene, so these objects are not blurred. There is an option to render translucent objects before the DOF is applied. This blurs the billboard, however, it leads to severe rendering artifacts (especially at the edges) because the depth information written by the billboard is not accurate enough for a good quality DOF calculation. For this reason, applying DOF to the billboard is not supported.