To provide the "helpful write-up" you are looking for, could you please clarify:
The string 21juakq87klo61 does not match widely indexed public documentation, which suggests it could mean a few different things: 21juakq87klo61 flv
did you encounter this ID (e.g., a specific competition, a website, or a file name)? To provide the "helpful write-up" you are looking
What is the of the FLV file (e.g., are you trying to recover data from it, or solve a puzzle hidden inside)? a specific competition