Many security camera systems generate sequential numerical filenames. "84299" could simply be the index number of a clip in a high-volume monitoring system.
Can you provide or describe the visual content within it? MP4 files explained: How to open and use - Adobe 84299.mp4
Screen recording software (like Windows Game Bar or specialized software like Guidde ) often uses timestamps or simple integers to title clips. Technical Profile 84299.mp4
If you encountered this file as part of an or a specific online mystery, it may be a local or obscure file specific to that community. 84299.mp4