This has a few “next level” odds and ends, including a bit of discussion about frame sizes. Here it says that this is mostly an issue when one is projecting a slide, because some projectors and screens are setup to work best with 4:3
Most computer screens are “widescreen”, so perhaps leaving the default for frame ratio at off is fine. Still not totally clear on when or why one would set it to 16:9 instead of just “off”.
Also noteworthy here is a method to add whatever is “on the screen” at the moment as an invisible frame to the frame path.
Invisible frames can also be added to your prezi if you click on ‘Add current view’ when editing your prezi’s path. This will generate an invisible frame based on the actual view that is currently filling your screen, and it will also add a step to your path.