Memory File Type
My dad changed all the old videocassette family videos into digital ones however when I splice them to show certain grandparents they save them as mp4 which the site doesn't take. Free software that is available via Google also saves them as mp4 so being able to upload mp4 videos would allow many to upload videos of ancestors from older recorded platforms.
To the best of my knowledge, FamilySearch does not support the upload of videos in any format. It's probably a size/resources consideration: video (multiple still pictures per second plus sound) takes a lot of bandwidth and storage.2
The other issue, from a very old post by someone from FamilySearch, is that screening videos to make sure they adhere to site guidelines just costs far too much at this point. Since they can't be screened for appropriateness, they can't be uploaded.1