fluttering screen

If you haven't rebooted the computer since the problem started happening, that's a great place to start.

If the problem persists, I'd check to see if there are any available driver updates for your graphics hardware.

If that doesn't help, see the section in the video troubleshooting guide about disabling hardware acceleration:

https://helpx.adobe.com/flash-player/kb/video-playback-issues.html

If you're still stuck, please follow the directions in the guide on providing the dxdiag report and include additional information about what you tested and saw.  It would be interesting to know if it's a Chrome-specific problem, or if it happens in other browsers, etc...