Whenever I used to import a video of me playing, it showed up. Now, the video doesn't appear for some reason. The computer I use is Macbook Pro (15 in.) running MacOS 10.15.3.
Hmmm...
Can you confirm which version of the SeeMusic app you are using by clicking the "?" icon? 2.4.2 is the most recent.
Does the video show up for any of your other pieces, or the 1st Sample Piece? ("Transcendental Etude No. 12 Chasse-Neige")
Can you try clicking on the Video File button, and then clicking "Confirm"?