Also in the USA. That cat video plays on Firefox and Chrome for Android, but if I open the link on my laptop and open the embed in a new tab (because I block ex

Also in the USA. That cat video plays on Firefox and Chrome for Android, but if I open the link on my laptop and open the embed in a new tab (because I block external scripts on my laptop), it "contains content from Jukin Media. It is restricted from playback on certain sites." So my guess in this particular case would be that something in Safari prevents YouTube from recognizing that the video is embedded on a site that bought an embed license. The more general problem with watching Japanese videos from the US is largely due to the fact that many Japanese media companies like to sell exclusive international distribution rights for all of their content, regardless of whether the buyer will actually distribute all of the content, or if the buyer is only going to use it in China or Korea. So they block their videos outside of Japan and we often can't find a version available in the US.