I'd like to have a way of taking a portion of some window (e.g. the video on a youtube page, or the progress bar of some program) and "streaming" just that part to a separate floating window so that I can see just that bit on another desktop.
I know that streaming software like OBS can do something like this, and I know that ffmpeg/ffplay can do this in theory (I could not get any examples to work). I also feel like it should be possible for the compositor to do this (like live alt-tab previews) but I couldn't find a suitable compiz plugin.
How can I get a second, separate view of a desktop program (ideally with scaling)?
(I'm on a standard install of Ubuntu Bionic.)