It resembles a unique identifier used by a server, a database, or a Content Management System (CMS) to index media.
It appears to be a highly specific, potentially private, or automatically generated file identifier rather than a publicly recognized media file, video, or viral content. 1621870012419002371 mp4
If you can provide the where you saw this ID, I may be able to help you track down what it relates to. It resembles a unique identifier used by a