Given you are using Safari 11.1, which is the latest release in any version of MacOS, upgrading the OS would be highly unlikely to effect this. I have encountered it recently in Safari Technology Preview Release 57 (Safari 11.2, WebKit 13606.1.18) which is later than Safari 11.1 but only on YouTube. It appears that a content blocker (ad blocker) is interfering with the comercial video that precedes so many YouTube videos which results in the message we are receiving.
Originally Posted By: jchusi
I disable extensions (easily done via the Develop menu, but you'll have to reload the page afterwards) and that works.
In Safari 11.1 that is unnecessary.
  1. On the Safari menu bar go to View > Customize Toolbar
  2. Drag the Website Preferences icon and drop it on the Safari toolbar
  3. Click on Done
After that any time you get the "THE VIDEO IS BAD…" message, click on Website preferences then uncheck "Enable Content Blockers". That disables any content blockers (which are the most likely reason for the error message) and automatically reload the page. You only have to do that once because Safari will remember the action and disable content blockers every time you visit that page. Disabling blocking is site specific and does not effect any other web site.

Safari > Preferences > Websites will show you site-by-site what you special conditions you have set including:
  • Using Reader mode when available
  • disabling content blockers
  • disabling auto-play of audo and video media
  • setting a site specific page zoom
  • disabling the camera (major security and privacy issue)
  • disabling the microphone
  • disabling location reporting
  • disabling notifications


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honestly, and you'll find people who are eager to
fill your head with information"
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