Over the years, I've seen various version of Acrobat make life simple while inserting videos, and other times have us all pulling our hair out over this. I just tried to drop a quick MP4 into a PDF, and the process went smoothly... until I tried to play it. I granted permission in the PDF, and it did nothing. But on maybe the 8th click, I heard the video's audio play with a static black rectangle showing! Although I don't have a solution., I can confirm that this feature did not work as it should for me either. I'll continue to see if I can figure out what's going on, and I'll post something if there's something tangible to share.