: A paper ID like 2106.076... might be what you're recalling.
If the term refers to the MP4 container or a specific encoding, you might be looking for papers on the standard. 21676mp4
It is possible the string is part of a DOI (Digital Object Identifier) or a specific database ID. For example: : A paper ID like 2106
The number 21676 appears in various contexts that may have associated documentation: 21676mp4