6181147.mp4.mp4 -

from 2018 regarding the BBC drama Wanderlust uses this exact number in its URL. It is possible a video clip from this episode was saved with the article's ID as the filename.

: A video was processed twice by a bot or script that appends the extension each time it runs. 6181147.mp4.mp4

: A user manually added ".mp4" to a file that already had a hidden extension. from 2018 regarding the BBC drama Wanderlust uses