I think I understand the WCAG 1.2.5 Audio Description (Prerecorded) rule, but what I can't find a straight answer on is if what if the per-recorded background video provides no real value, like if it's just a short video of someone walking on a loop with no talking/audio. Does this rule still apply?
Assuming the video serves no purpose other than decoration then you are safe to hide it with aria-hidden="true".
While the above is perfectly valid for accessibility, there are other considerations from an accessibility perspective.
Do you provide a way to pause the video? If someone has an anxiety disorder then the video can be distracting so you must provide a way to pause the video. (or you could use the Prefers Reduced Motion media query and use that to stop the video auto playing, however the support is not fantastic at 80%.)
You should also add the muted attribute to indicate that the video has no sound to screen readers.
If the video does provide a purpose (i.e. it emphasises what the company does) then you should add a description to the video using aria-describedby and pointing that to a hidden <div> with a description of the video contents as a minimum.
If the video is purely decorative, has no meaning within the page and is there just to 'look cool' perhaps consider replacing it with an image. It will massively help your page load times and so can only help with conversions, video backgrounds hurt more than they help as they take focus away from your call to action.