Okay I just happened upon this video capture from OpenSimulator so checked to see whether it would actually work, and it did:
http://worldoflittlefield.wordpress.com/
It is just a video imbedded into a blog page, yet it actually managed to work.
They seem however to have blocked "view source" somehow so maybe if wordpress doesn't do that itself normally and it isn't just something they got, possibly without even realising it, as part of some template they used for their blog, possibly it might be the work of someone quite sophisticated who knows what they are doing.
Hovering it and rightclicking it and so on it seems that it is HTML5.
Someone said earlier HTML5 is actually not widely viewable though so maybe i have one of the few browser brands that happens to support it (Firefox)?
I think though my other browser, that I almost never actually use (Google's browser) also supposedly supports it. So I am not sure what doesn't support it?
Maybe Windows only supports some in-house variant of it? Or doesn't support it at all?
I don't usually even try to view videos because historically they almost never worked, even on machines that did have some old version of flash installed.
I don't have flash installed at all and that blog video works fine.
it is even on youtube, i just noticed! Though, again, maybe someone sophisticated had to force youtube to do it this way instead of some other format.
(Or maybe youtube detects the browser and pushes a version it knows the browser can use?)
-MarkM-