By “opaque” do you mean black? If that’s the case, there are multiple ways. You can use transfer modes(press F4)—try the additive ones like Add, Lighten, Screen, Color Dodge, Classic Color Dodge, Linear Dodge, Lighter Color. The help describes what each one does precisely. Transfer modes are nice because they will blend with the layer below.
Another method would be to use a luma key effect or extract key, both would easily remove the black from your burn marks video.
Johnny Cuevas, Editor
Thinkck.com
“I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
—THOMAS EDISON on inventing the light bulb.