This part... doesn't exactly make sense. Flash video, be it *.flv or *.f4v can be h.264 encoded. Flash has less to do with video since it accepted a wide range of codecs; it required the Flash Player plugin.

With that said... Flash cannot be fully replaced as of yet by HTML5 alone. It takes lots and lots of jQuery. Canvas isn't fully supported across the browsers. So the nice vector based animations aren't friendly across the board yet.

Flash is more than advertising banners too. I can directly query a DB among other things that I cannot do in HTML5 fully... yet.

But the <video> tag fight about codecs is far from over.