Unable to include stage package

I have a missing .so file, libDeckLinkAPI.so.
When I dpkg -S libDeckLinkAPI.so I get desktopvideo, so I added desktopvideo to my stage-packages location. When I try to run snapcraft, I get the error

Failed to fetch stage packages: Error downloading packages for part ‘myapp’: The package ‘desktopvideo’ was not found…

I’ve done sudo apt-get install desktopvideo to make sure it was on my computer, just in case, but the the problem persists. Is there a different way/package I should be including this?
I think I could solve it by copying the .so file into some writable location once the snap installs and then add it to $LD_LIBRARY_PATH, but that doesn’t seem like the way it should be done.

The desktopvideo package isn’t found in the Ubuntu software archive, it must be from a third-party software source. In order to use it you must setup one.