I wondered why the page was full of blank areas, it's because of this:

https://caniuse.com/hevc

... the videos are hevc-encoded and don't work for me in eg firefox. (I can see them if I switch to chrome)

per ffmpeg:

    Stream #0:0[0x1](und): Video: hevc (Main) (hvc1 / 0x31637668), yuv420p(tv, bt709, progressive), 1080x656, 1219 kb/s, 60 fps, 60 tbr, 15360 tbn (default)