Q: HD youtube video not playing in safari

I have the exact same issue. Every other browser and device works fine, but in Safari, it just starts playing for couple seconds and then freezes with the spinning wheel. It seems it does this only for the HD version of the video. I tried downloading the video and uploading it again, didn't help. Embedding the video on a site does the exact same thing.

Open System Preferences > Flash Player then select the Advanced tab the click Delete All under Browsing Data and Settings. Quit then relaunch Safari and try a video.

If that doesn't help, make sure OS X is up to date.

Open the App Store then select Updates from the menu.

Thank you for your suggestion, however none of these fixes worked. I am running the latest version of everything:

OS X - Version 10.11.5 (15F34)

Safari - Version 9.1.1 (11601.6.17)

I cleared the Flash data and still nothing.

Thank you,

Martin

I have the exact same issue. Videos that will not playback in Safari while on YouTube do playback on every other browser.

Safari - Unsupported third-party add-ons may cause Safari to unexpectedly quit or have performance issues

Safari doesn't load a page or webpage items are missing

Safari/other browsers – Website not loading

Eric,

What you just posted has absolutely nothing to do with this issue. This issue occurs on a brand new clean install of El Capitan 10.11.5 with no addons. There is also more than one post about this exact issue in the community. Have a Google search.