This usually refers to a User ID or a Device ID. In security systems, this identifies which camera or hub recorded the footage.
Because this is a specific, unique filename rather than a public media title (like a movie or viral YouTube video), it is likely a personal or private file. Here is an informative breakdown of what this file string represents and how to review its likely origin: File Naming Breakdown 61414-501608066786_f_1611581559.mp4
Systems like Hikvision or Dahua often export clips with long numeric strings that include the date and time of the incident. This usually refers to a User ID or a Device ID