Share an area of your screen by using vlc screen capture, and then sharing the vlc capture window
Make sure the VLC window floats
In i3 config:
for_window [window_role="vlc-video"] floating enable move down 100px;
We float it so the tiling window manager doesn't resize the window and mess up the scale. We also move the window placement down at launch so it easy to drag somewhere mostly offscreen.