So better show you how it works for now. It is still quite buggy, and not really ergonomic, but it is the beginning!
Here is the video (of course edited in Pitivi and using effects!):
You can grab the code here if you want to give it a try even if it's not ready for production...
So next week I am going to clean up the code and of course fix the bugs I find. If I have time, I will start working on the UI part.