Hey, so I think the problem you are having is because you are using a video in the media plate. If the video is not playing, it will just appear black. I had a similar problem when using a webcam as a source, it has to be started up for it to appear.
You got it to start playing when you had the media player window open, but when you close the window it stops playing so your “media plate” goes black. Open up your media player window and get it to start playing in a loop there, then leave that window open and go back and look at your media plate, you should see the video playing there now. I’m not sure if there is a way to make it keep playing when you close the media player window (there probably is, I just don’t know it). To get it to play when you actually run the game, you need to put something in the level blueprint to start it playing.
The reason some things are not all that straightforward is because this is a game engine and not a video editor, a game might have tons of different videos in it and they can’t be playing all the time, even in the editor, something has to tell them to play.
By the way, if you get the weird green corners like you see in some of the composure samples, this is from devignetting in the chroma keyer. This is for correcting for cameras where the outside of the image is slightly dimmer than the center. I think if you set the first devignetting value to 1 and the others to 0 it will look ok, you may not have to do this, I’m not sure what the defaults are.
I went ahead and setup the chroma-key and it looked pretty good, there is a bit of a green edge around your character, probably because whatever you used to make the animation was doing some smoothing of the edges or maybe just because the video is compressed. The quickest solution for this is to mess with “erode” in the keyer which will just bring in the edges of the key a little bit. Eventually though, you can probably setup your animation program to output a video with an alpha channel and render your character with a black background instead of a green one. I haven’t played with alpha channels in video much, but if your animation program can generate one, composure can use it INSTEAD of chroma keying and the results should be better.
Greg