Hm. Okay, after searching for "what really is problem, because program is too stupid to say it properly" I think I found a problem.
Movie as from files in my player works as intended, but from WE doesn't, because W7, because 4k...
I apologize for my bad comment.

@Cylindryk: Sorry to hear my wallpapers don't seem to work for you, afaik they are working for most other people, certainly for 3440x1440 ultrawide native resolution users. If you're using win8.1 or 10 and have 3440x1440 native res and my wallpapers still don't work, let me know, cause they certainly work when I create them, I check every single one of them to make sure. Also, any subscribed wallpaper is stored at C:\Program Files (x86)\Steam\steamapps\workshop\content\431960 any video wallpaper will be stored as .mp4. I suggest check to see if you can play my wallpaper videos under something like MPC-HC make sure you have proper codecs installed (K-Lite). Other things worth checking is to try some one elses 3440x1440 wallpapers and see if they work for you, but if mine don't work, I doubt you can get anyone elses to work. May also want to check with WE FAQ and perhaps even check forums posts to problems similar or post directly towards the devs yourself.

You know that almost none of your items works, right?