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Sorry to drag up an old thread, but I had a similar problem, albeit with Vimeo HD videos and only when played full screen. Hardware acceleration was already enabled in the Flash player settings, so I disabled it and refreshed the page to see if it made a difference. The logical outcome would be that it would get worse, but it actually fixed my problem completely. There's a couple of skipped frames, but it's immeasurably better than the slideshow that I had to put up with before.

Strange thing is, I had this problem before I replaced my hard drive late last year. After reinstalling everything the problem had gone away and at some point in the last few months it started again. This leads me to believe it's not hardware related, but some poor coding from Adobe.

For the record: Macbook C2D 2.2 Ghz, X3100.
 
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