mepj to mp3 conversion is almost certainly related to export of Movavi Video Editor projects (.mepj) to MP3 format, to be more specific, just the export of the audio track. No other software can work with .mepj files, so it's not like you have choice in this matter. Of course projects require access to the multimedia content referenced in them, as without the original data there is nothing to export.
Updated: August 10, 2023