Sounds can be really difficult to distinguish on video. Mics alter frequencies, and phone mics are bad for that.
Main bearings usually make a sound on start-up, then typically go away when oil hits them. Rod bearings typically make sounds all the time, or at RPM. Wrist pins typically make sounds only when the RPM is increased. None of those seem to be the case here.
First thing I'd do is try to pinpoint the location of the sound. Use a long screwdriver against the ear, or a piece of tubing or something to place against your ear and try to find the loudest area. Having said that, if it's coming from the valve cover area, it sounds as if it may have a loose rocker. Is it a solid lifter engine? Might just need an adjustment, hopefully. I'd pull the cover on the offending side, look for any issues like abnormal wear on the valve tip, loose rocker etc. If it's a hydraulic cam, feel for any spongy rocker movement while shut off and the valve is closed.
Might also be the fuel pump. If the spring is bad or missing, on the arm, they can make some serious racket. The "stethoscope" should find that one pretty quick, if that's the case.
To me, it sounds valvetrain related.