Platforms like Cloudinary or Imgix use these strings to track assets. If you found this in a website's source code, it is being served from their servers.
.mp4 (MPEG-4 Part 14), a standard digital multimedia container format most commonly used to store video and audio. Naming Structure: 5ef510cf47d2ad7193eea_source.mp4
To provide a more specific report, could you clarify or share the URL host where it is located? Platforms like Cloudinary or Imgix use these strings