Embed videos in presentation

I am on a MAC running OSX 10.11.5
LibreOffice (I am in the middle of a job, so I wouldn’t really like to update LO to 5.0 if not absolutely necessary as I wouldn’t want to mess up my work…)

I am trying to embed so mp4 videos, but when I do that all I get is a grey box with a BIG question mark on it.
on the plus side, I have managed to load a gif though.

I have been reviewing some older posts and people ask about the codec, but I am not sure where to get that info.

(Am I working with Impress? I don’t find that name anywhere… But people seem to use it and I cannot find any suitable alternative among the compulsory tags to choose from)

Presentation is made with Impress. The program names aren’t exposed normally.