I've been using OpenLP for years now. I've ran OpenLP on Linux, Windows and Mac. One of the features I've been trying to get is Motion Backgrounds for my Songs.
I have found a SIMPLE way to convert mp4 files to gif files, and gif files can be used as the image background for songs with OpenLP 2.9.4.
I've been using AVS4YOU [https://www.avs4you.com/avs-free-video-converter.aspx] out of the UK for all my video and audio purposes for years. Believe it or not, their AVS Video Converter 12.2 will convert mp4 to gif. And these gifs work great in the OpenLP 2.9.4 Themes on Win 10.
Try to find a motion in a mp4 (1920x1080 px) that is not obvious when it loops, and is 30 seconds or less to keep the size down. For example, a mp4: 8 MB in size with a 20 sec loop will make a gif about 137 MB in size. I have about 8 motion backgrounds and one gif is 710 MB in size but it still works good in a Theme for songs on Windows 10.
I do hope this helps and encourages others to use motion backgrounds with the new OpenLP 2.9.4