Lookin at the FAQ..
FAQ 12: Why can I only upload one image?
FAQ 20: Trust Levels
Ohh and in fact the limit of 5MB is mentioned.. here:
You seems to be no “new user” anymore but “basic user” so you should be able to do so if respecting those “limits”.. ( maybe you was just recently advanced to basic because your activity shows only 11 days visited in the last 4 years ??)
..and uploaded videos are only directly embedded if being mp4. For images i do not know some format limits.. but png and jpg (used myself) (and animated gifs ← have only seen this) work..