Direct link to the Keynote youtube stream: https://www.youtube.com/watch?v=wtLJPvx7-ys
Disclaimer: I work in the video space.
[1] http://stackoverflow.com/questions/21921790/best-approach-to...
That's a very bad way of stating it. It's perfectly possible, and "supported" even though there is no "use this thing" solution for it. The problem is that you can't rely on a full solution being usable by all browsers you want to target.
They all do the same thing fundamentally; the only differences are slight technical details and who is in control of the standard.
[0]http://ie.microsoft.com/testdrive/graphics/videoformatsuppor... [1]https://www.youtube.com/html5 - This shows 6/6