That video frame shows the top of the Apollo LES. The object under the cover is the Q-ball. The cover is removed at T - 9 s.
The Q-ball is an angle of attack sphere perched above the launch escape system,
The Q-ball is not unlike a pitot tube on an aircraft that measures airspeed. It consists of eight openings at the top of the Launch Escape Tower. These openings lead to instruments which gauge air pressure.
This paper has more information:
The Q-ball has eight static ports (openings) through which pressure changes are measured. The instruments use this information to determine aerodynamic incidence angle and dynamic pressure data. The instruments send information on the angle of attack to an indicator of the CM's main display console and to the launch vehicle guidance.
The pitch and yaw pressure-change signals are electronically summed in the Q-ball and displayed on the indicator. The Q-ball information provides a basis for crew abort decision in the event of slow launch vehicle divergence.
Herorelics has photos and can tell us why there's a cover:
While on the pad, the Q-ball is protected by a cover to keep the ports free of dust and debris.
This is the LES with the cover on top:
Vintage Space has a video that explains the LES, the Q-ball and how the cover retraction mechanism worked. And the origin of the name: Q is the symbol used to indicate air pressure (think max-Q).