I wonder where the video is hosted on? Oh I see on the URL in your post (cdn.nostrcheck.me/xxx) so that's probably the default.

I use nostr:nprofile1qqsfnz2sqsflkatdssmeztxr90s8xrd7r07xkhfwaa6eu9zkcguljpgprdmhxue69uhkummnw3ezuur0wf6x2mt0dejhymewvdhk6qgjwaehxw309ac82unsd3jhqct89ejhxqgcwaehxw309akxjemgw3hxjmn8wfjkccte9e3k7mg2kf0ae for hosting. #Amethyst displays my video well.

However Nostrudel doesn't, complaining about the video format being incorrect (although it's clearly listed on my Videos section on my profile). So all clients need to agree on this is my understanding...