2 ThinkPads, X200 and X260.
Both Artix, both i3 with the exact same rice, both 8 GiB of RAM.
However, on the X200 whenever I run a video in MPV, it suddenly starts using up all of the RAM and Swap in a matter of a few seconds, and never releases any of it until I reboot the entire PC, no issue with music files though.
On the X260 on the other hand, there's no such issue.

Really weird...