Real Time personalized videos
This is effectively a streaming media server tied to a live renderer.  Rather than save a recorded video, when you make a request for the video, it accesses a live stream.  That live stream uses the contents of the request to run a template video and encode in real time.  That real time stream is then played for the user.

You could probably manage to wire something like Red5 up to be able to do this with some alterations.  The big trick would be kicking off the live stream as part of the processes.  You also need sufficient rendering hardware to be able to generate a distinct live stream for each request.  You also need a real time video rendering system that can work with templates.  There is tech like this for video mixers, but I'm not sure of any particular software that does it in software in real time.  Some streaming oriented software may be able to do it though.