Firstly, my thanks to you for creating such a great site!
I've recently been running the site on my 2nd monitor while I'm working and noticed an interesting quirk after trying to use it in Fullscreen mode - It appears to be zooming into the middle of the video. Trying to troubleshoot a bit I took a side-by-side screenshot of the Kyoto Walk on the site on one screen and the YouTube video on the other with them closely synced together. I then checked the sizing of the site's image against the YouTube video and discerned that it appears to be a zoomed in window of around 640x360 in the centre of the original video. Checking the source of the site I can see the YouTube iframe appears to have a width & height definition of 640x360. Might this have something to do with it?
I did also check I wasn't completely crazy and tried the site in different browsers (Chrome first, then Edge and Firefox), and also with the 2nd monitor disabled, and got the same result each time. I tried to replicate this on another PC but it didn't have the same problem, whereas a remote desktop session I have access to... does. Quite an odd one.
Edit: I've realised that the Kyoto Walk video is 3840x2160, as is the display on the 2nd PC I tried to replicate the issue on (the others I mentioned are only 2K screens). I dropped the screen resolution down to 1920x1080 on that PC and sure enough it zooms in on the video when going fullscreen now.