Rendering Smoke, Bloom or Volumetric Lighting with an alpha layer in Eevee is not straight forward – but it’s not that hard either. These little tutorials assume you’ve already have your scene set up, and are now hunting for that elusive transparency.
The next step in this tutorial series is Glass - which will be a whole 3 tutorials all to itself, depending on whether you want refractions, and whether you want to refract the background video.
I'd like to see eevee motion blur. At the moment I have to use Blender Internal for that...