I had this issue this morning after installing Flash Player Update 10.3.181.14 and wanted to share info and fix. I had to disable hardware acceleration in IE9 to make my video playback work properly. Please see link for info and fixes.
http://blogs.adobe.com/flashplayer/2011/05/reported-issues-with-flash-player-10-3-and-internet-explorer-9.html</span>
http://blogs.adobe.com/flashplayer/2011/05/reported-issues-with-flash-player-10-3-and-internet-explorer-9.html</span>