A Matroska Video file extension , which is an open-standard container format that can hold multiple video, audio, and subtitle tracks in a single file.

The string contains several distinct components that describe its encoding, source, and content:

This prefix is a standard way to indicate that the following text is encoded using UTF-8 , the most common character encoding for the internet. The two single quotes often appear in Content-Disposition headers (RFC 5987) to handle special characters in filenames during downloads.

A reference to Openload, a formerly popular file-hosting and sharing service often used for user-uploaded media. Episode Details: " Pound of the Baskervilles " UTF 8 filenames? - Unix & Linux Stack Exchange

The title of the specific episode.