Random alphanumeric strings like this are often generated when someone is bored or "keyboard mashing" to see if a unique result exists in search engines.
It could be a specific, non-public identifier such as a serial number, a unique database ID, or a specialized font/asset name used in a particular piece of software like Affinity Desktop or Geant4 . 9739mp4
The "mp4" suffix typically refers to MPEG-4 video files , while "solid text" might refer to a specific styling within a video editor or a type of encoding error where text is rendered incorrectly. Random alphanumeric strings like this are often generated