Thankyou! In my initial post, I did say that VLC works normally if it's not launched from Terminal. Sorry if I waffled so much that it became unclear. I'm a bit hungover today so not firing on all cylinders!
For what it's worth, the script is working fine, as you can see:
I just tested by adding a random video file to the folder (a jazz guitar lesson 
) and it's getting the size just fine.