: On a Windows PC, right-click the file, select Properties , and go to the Details tab to see if there is an internal "Title" or "Author" tag.

: Take a screenshot of a unique frame from the video and upload it to a reverse search engine like Google Images or ImgOps to find where else it exists online.

: You can generate an MD5 hash of the file and search for that hash online; if the video is popular or from a known database, the hash may lead you to the original source.

: On Android, instead of just opening the file, tap the three dots on the media in Telegram and select "Save to Downloads" ; sometimes this triggers the app to save it with its original descriptive name.