I think Microsoft have removed the option to use transparent background videos in the latest versions of PP.
Below is an animation I have just created of a slide with a 'water' image as a background picture with a school of orange fish (.avi format/transparent background) swimming across the slide.
It works fine in PP 2010, but the same slide when opened in PP 2016, displays the black background you see in your video.
Creating the same slide in PP2016 with transparent background video immediatly shows the black background.