The final .mp4 is the actual extension currently recognized by your operating system, which is the most widely compatible format for smartphones, smart TVs, and web browsers.
The sequence typically indicates that the file was originally a Matroska Video ( MKV ) file that was converted into an MPEG-4 ( MP4 ) file. XX EPi 2.mkv.mp4
The "EPi 2" suggests this is the second episode of a series or season. The final
"XX" is frequently used as a placeholder in temporary or newly downloaded files before they are properly indexed by media management software. XX EPi 2.mkv.mp4
Many automated conversion tools (like OBS or MKV2MP4 ) append the new extension to the old filename by default rather than replacing it. Likely Content and Origin