<sigh> You guys aren't really as daft as you're pretending to be.
Hardware acceleration of H.264 video has been baked into Macs prior to Snow Leopard. H.264, as you should probably already know, is the chief competitor to the Flash FLV video format. The VDA API has never been necessary to get hardware acceleration for H.264 video, only for Flash FLV.
Ergo, Flash video's primary competition on the Mac (and iOS devices) is a video standard that already had hardware acceleration out-of-the-box with any Mac/iPhone/iPod Touch of recent vintage.
As others have mentioned, you apparently don't understand how software interacts with hardware.
Yes, H264 hardware acceleration existed prior to 10.6.3, but was not available for use outside of Quicktime. Read that one more time.
Yes, there was hardware acceleration for Quicktime.
But you can't use it for playback outside of the Quicktime framework.
Now, I'm guessing the first thought that springs to your mind would be "so yeah, it's there and Quicktime is a public api there, so use it!"
Doesn't work that way.
Quicktime takes files that it understands and plays them back. Hardware acceleration typically requires shortcuts and all sorts of crazy layer-breaking that would have made it nearly impossible to integrate into a browser.
Think about it this way, ever seen on a PC or a Mac when somebody's playing a hardware accelerated mpeg or h264 movie in a scroll view? And you try to scroll it only to find stuff inside the scroll view scrolled... except a black box comes out underneath and the movie keeps playing like it's hovering over the entire thing? Yeah, that's one of those things that people have to work around.
It's a bug, and people don't fix it by making it work.
They make it so you can't do the thing that caused it.
In short, prior to 10.6.3, use of hardware acceleration where possible would have been a crap experience when we talk about it in the context of a movie in a web page.
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Good, so you accept my original point then - Flash's poor performance on Mac OS X was entirely Apple's fault.
Incorrect.
Flash's poor performance when playing back H264 video was entirely Apple's fault.
Flash's poor performance elsewhere was the fault of either/or Adobe or the programmer who wrote the SWF file that you're playing.
Afterall, somebody who makes SWF files as their primary coding environment probably doesn't know why their spinlock is a bad idea.