I've spent a few hours looking into this problem and only seem to be able to find rather old references to it. Im using a 64 bit build of CEF/Chromium 1916 on OSX in OSR mode and I can't get embedded flash playing properly. We previously used Awesomium for our game (which I believe is based on Chromium as well) and the same pages worked just fine (although admittedly, I've never seen them work in Awesomium on OSX). The references I've found so far mention putting --disable-accelerated-compositing on the command line, which I've tried. I've also found mention of adding wmode=opaque/transparent to the web page, but I don't have direct control of the pages being displayed, so this isn't really an option at the moment. I know this was a known issue - is it still?
What is happening is that the area where the video plays only gets updated where the time track handle moves, except if I wiggle the mouse over the page when the whole video area updates. This leads me to believe that I need to pump some regular event to it, but I can't find anything in the documentation about having to do that, and the only function I can find that looks like it might do what I want is CefBrowserHost::Invalidate().
Any help with this problem would be greatly appreciated.