The easiest way I found to do this was to take a dot product of the texture and the color you want to remove. If it’s higher than a given threshold, output opacity 0, otherwise, opacity 1 (or you can blend it with a lerp).
EDIT:
Here’s a quick test material I threw together. The texture is a rather blocky jpeg hence the low quality.
Sorry yes Furroy, I want the green to be completely transparent but I do not want the non green to be and using Blend translucent and Additive makes the non green semi transparent.
haha, well i’m confused. earlier you specifically said you had black backgrounds. or do you have green? we can try to tailor an approach once you nail this down 
This is true because unfortunately for me, I have both I need a solution to handle both.
meaning I have some videos with black screen backgrounds and some with Green screen…
DamirH thanks for the help I tried your approach, have you ever tried your technique with a video Texture it is bizarre because I can remove ever color in the video texture but the green and or black background, I have know clue why this is but I followed your steps to a tee and that what was happening to me.
polemos:
Any progress on this?
I am trying to set up some level of video with transparency in UE4, and I’m running into similar problems.
I’ve found that trying to output a second video with the alpha channel to animate with the other doesn’t work since the two video playbacks don’t sync up. I’m looking into Bink as a possible middleware solution, but wanted to see if anybody had figured out a solution to this problem.
no still working on it I have yet to perfect this I get close but nothing is perfect yet, what about you?
I did it and Im not getting any of the speckling at all. might be because my video texture is a simple color changing symbol
can you post a pic so I can use as a reference?