I recently discovered that at least one of the slideshow videos has some faulty slides with most of the pixels missing when generated on an older laptop. This happened repeatedly. When I ran it on a faster desktop computer, it came out OK.
The problem computer bench marks at 2502. The desktop that it worked on at 9607.
There were no error messages on the video creation.
So be warned that when making the longer videos if your computer is slow, it is good to scroll through the video to check for problem slides.