Mixing two videos together with blue screen aka chroma key

[hoho]

I have two video streams: one is the background, other is foreground filmed against green screen. I need to mix them together in real time and show the result. For now I don't have the actual streams from real cameras so I need to test stuff with regular files.

I've found the tutorial from wiki but it doesn't seem to work with the sample files as has been found out earlier. Corresponding ticket has been open on track for 10 months no with no further comment so I guess no hope in getting the problem fixed any time soon.

I tried converting the sample files to YUVA but couldn't manage it, possibly because of not having enough experience with VLC. Closest I got was YV12 but VLC requires YUVA and I couldn't find any way how to output files in that format. I'm also almost certain the cameras that will be used eventually will be using some other format so some kind of conversion will be needed.

So, my question is what should I do to start testing chroma key functionality with VLC? Is it even possible with current builds? If not then are there any alternative ways I could achieve my goal that would work with CLI instead of fancy GUI in some editor?