Q: Why does youtube not work properly on Safari

YouTube requires Flash so make sure Flash sup to date.

Open System Preferences > Flash Player then select the Updates tab then click:  Check Now.

And make sure OS X is up to date. Open the App Store then select Updates from the menu top of the App Store window.

Hello !

            Suggested articles are to be followed :

Safari: About Internet plug-in management - Apple Support

Adobe Flash Player updates available for OS X on June 20, 2016 - Apple Support

Thanks !

Try un-installing and then re-installing.

Adobe Flash Uninstaller

Adobe Flash Player

You guys are falling behind please sort.

Please understand you are talking to other end-users like yourself here, not Apple.

If you wish your concerns to get to someone who gets a paycheck from Apple, please use this link:

http://www.apple.com/feedback/safari.html

However, I believe that if you follow the sage advice already provided here, you will not need to use the link.