I believe vp9 will work from FF and chrome for more than 6 months (FF, chrome longer). There are still no plugins for IE and, of course, no built-in support.
Hevc (h.265) does not have built-in support, but there are plugins from divx.
So, it is best to discover the possibilities with html5 using vp9, and then return to mp4 (html5) and then continue backing up to flash (possibly mp4).
Thus, it is not possible to deliver only h.265 and / or vp9. The best you can do is deliver vp9 to about 50% of the world's population and leave a reserve for the rest.
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