In the past, numeric filenames like this were used for These files used specific encoding tricks (like an impossible aspect ratio or frame rate) to make a user's app restart when they viewed it.
If you have downloaded this file and are unsure of its contents: 4157917686082953309 mp4
Give it a descriptive title (e.g., funny_cat_meme.mp4 ) while keeping the .mp4 extension. In the past, numeric filenames like this were