To use: Place the map file into PAYDAY 2/Maps Convert your desired video file to .bik with RAD Video Tools, rename the created ".bik" file to "the_end.movie". Place the mod "Large Movie Theatre Screen" into PAYDAY 2/assets/mod_overrides/, and your created "the_end.movie" into Large Movie Theatre Screen/movies.
Just a matter of note: everyone in the lobby has to have the same movie file as you if you REALLY wanna do this properly, custom videos do not stream over the internet.
Thank you to Columbus for making the screen larger and Rainbowfishcakes for redoing the entire mod structure to be more intuitive =)