Safari 8.0.6 gives error message whenever going to a YouTube page.

Hi iflyalot,

I see that you are experiencing an issue with YouTube in Safari on your Mac. As a troubleshooting step to begin addressing this issue, I would recommend that you make sure your Flash player is up to date:

Adobe Flash Player updates available for OS X on April 21, 2015 - Apple Support

https://support.apple.com/en-us/HT202681

You may even want to uninstall flash, then reinstall in order to thoroughly test this behavior. Hope this information helps, thanks for using the Apple Support Communities!

Cheers,

Braden

I am wondering if this if from quitting Safari without closing the windows containing tabs.

I am able to open a fresh YouTube page and not get this message.

It appears you have answered your own question.

Please bear with me, as I'm not very familiar with web tools and video formats. But I do agree with iflyalot; with my configuration (safari 8.0.6 and OS X Yosemite 10.10.3) I can only watch one you tube video per tab. If I attempt to watch one and then load another, I get the error message about html5. Opening multiple tabs will work in a pinch, but this is cumbersome and clearly not the way this should work. In terms of flash (assuming its relevant) it appears that it's not available from Apple's site. Is that correct? Do I need to go to adobe to get this?

Thanks for your help.

Yes and Yes. Only download Flash Player from the Adobe site. Other downloads other web sites can cause problems. Link to Adobe.

Adobe Flash Player

Thanks, Eric. I did upload the latest version of Adobe Flash but I continued to have the problem. If I view a video in the same tab that I used to watch a different video first, and the HTML5 error message comes up. If I open a new tab (testing with the exact same video) it works fine. The error message is: "Your browser does not currently recognize any of the video formats available. Click here to answer our frequently answered questions about HTML5 video". Following the link indicates that Safari supports HTML5. I should add, this isn't a problem with all the videos, but is with over half of them.

You are welcome.