MEPJS format is used for projects in Movavi Slideshow Maker and this is the software you have to use if you are looking for a way to export these files, in the case of mepjs to mp4 conversion, this would be export of the slideshows to MP4 video animations. You will need access to Movavi Slideshow Maker version 23 or later for this, because there is otherwise no alternative.
Updated: August 28, 2023