Hey guys, I found this. Might work...

Ot appears to be on the Youtube side and here's the solution that's working for me.

Unhide the Develop menu, then change the User Agent to something other than Safari 5.0.3--MAC. I set mine to Safari 5.0.3--Windows and the videos play correctly.

To unhide the Develop Menu:
Preferences/Advanced/Check the Box to Show Develop Menu in the Menu Bar

Once that's done, select Develop/User Agent and make any other selection besides "default" or "5.0.3--MAC".

With each new window or tab, you will need to change the User Agent, but at least this may work for you until whomever is asleep at the wheel wakes up.