You may try my PiPlayer , which is basically a window wrapper around omxplayer. You can move, resize it, etc, but cannot move anything in front of the omxplayer overlay. Also you could use it to stream directly from twitch (but then omxplayer gets very slow to react to inputs) and videos from youtube (with smtube).
You would need py-fltk though, which can be build and installed using that handy bash-skript (at least I hope it still woks). EDIT: I believe py-fltk is available through the normal Debian / Raspbian package sources, so building it "by hand" might not be necessary on a normal Raspbian.