1. Install Adobe Flash Player.
2 .Are Plug-ins Enabled?
Safari > Preferences > Security
Click in the box for "Enable Plug-ins".
3. Check whether you are currently in YouTube HTML 5 trial.
At the bottom left of the page uncheck the box for
"You are currently in the HTML5 trial".
4. Reset Safari.
Click Safari in the menu bar.
From the drop down select "Reset Safari".
5. Turn off Extensions.
Safari > Preferences > Extensions
Now try YouTube.
I noted that you have opted out of HTML5 trial.
Hope this helps.
I've done all of those things except disabling extensions, which I have no desire to do. Current browsers are clunky dinosaurs without the extensions.
By the way, I was opted out, now I'm opted in because I tried to use an extension that converts all youtube files to html5. Neither one is doing any good.
I think I'm just going to have to use multiple browsers for different needs. Which is pathetic, but you gotta do what you gotta do, right? Thanks for the help though; I appreciate it.