“It does the same on several older and new Macbooks around, so not sure about the effectivity of this procedure. And will it enable playing 4k videos in 4k resolution ? I think it is rather Apple who should clean all this and provide a serious browser ?”
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Why this is Relevant:
Clearing your Temporary Internet Files would make Safari open each page anew. So, site-entered data, and selected items, would not be there, including YouTube in this matter. As Safe Mode, booting into to, items open as the would by default, with all preferences set aside. Also, Login Items would not open at login.
Update your Mac & Report this:
If Safari is not playing those videos, then check your Mac for updates. If 4K won’t play with Safari, but will on Firefox, then either check for Safari updates, or wait for the next update. This has been an ongoing bug; one posted on the forums quite bit.
So,...
Do your Part — Report it to Apple:
So, provide your feedback about this Safari issue. Mention what you been through, and how you have gone about troubleshooting it thus far.
- Go Here: Feedback - Safari - Apple
- Select: “Bug Report” for the “Feedback Type”
- Proceed from there as Necessary