The documentary is a short, but interesting look at the background to the project. There's a segment talking about how a missing piano piece by Richard Wright was investigated, and you hear this piece highlit on the soundtrack. Elsewhere, Storm Thorgerson talks about the packaging for the new edition, and explains how they came up with the idea to return the original pictures to the elements represented. So, the picture of the burning man gets burnt itself, the splashless diver picture is itself under water, and so on.
You can view the documentary on Youtube, and we've also embedded it here: