Screen mirrors into two exact halves whilst watching media online using Safari 14.1 - OS 11.1

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Level 1

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Screen mirrors into two exact halves whilst watching media online using Safari 14.1 - OS 11.1

Last week I bought a new 2020 iMac 27", i5 3,3 GHz 6‑Core, Radeon Pro 5300/4GB GDDR6, 40GB RAM and immediately updated to Big Sur 11.1 and Safari 14.1

Watching Netflix movies in Dolby Vision (4K HDR) in Safari and then within a minute the screen mirrors into two exact halves. After quitting Safari I then realise that has also done the same with the finder desktop etc. And no, it isn't the window splitting function. I have exactly the same system OS and Safari on my work iMac 27", 2017 and tried to reproduce the exact scenario but no glitch.

I am specifying Safari Dolby Vision (4K HDR) in particular because the glitch doesn't happen, with the exact scenario using Firefox or Chrome on the effected iMac, they don't support Dolby Vision (4K HDR). I have attached two videos to better show what I am facing. I have not, even after scouring the internet and here, found any posts regarding this strange glitch.

https://youtu.be/yiiP3vLXiF4

https://youtu.be/Lgc9z3pVfT4

iMac 27″, macOS 11.1

Posted on Dec 17, 2020 3:08 AM

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Answer 1

Top-ranking reply

MichelleT18

Community Specialist

Dec 20, 2020 11:21 AM in response to ukstanng

Hello ukstanng,

Thank you for using Apple Support Communities!

Based on what you mentioned, your display on the iMac splits in two when using Safari and enabling 4k HDR. Check this option from the instructions below.

"Choose Apple menu  > System Preferences, then click Battery or Energy Saver. If “Optimize video streaming while on battery” is selected, your Mac saves energy by playing HDR video in SDR while on battery power. To play in HDR, connect your Mac to power or deselect this checkbox. " - Play HDR video on Mac

If you still see the issue after, test if you have the issue in a new user account. You can set up a test user. For help, review: Set up users, guests, and groups on Mac.

Best wishes!

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Answer 2

karina184

Community Specialist

Dec 21, 2020 10:22 AM in response to ukstanng

Hello ukstanng,

Thanks for the additional information.

If you are seeing this in your test user, it would help to know if you have the Developer menu enabled for Safari. Learn more here: Use the developer tools in the Develop menu in Safari on Mac.

If you've made any changes there, you'll want to make sure you've made the right selections or configurations.

If you haven't made changes in Safari's Developer menu, you may be able to get help where you are when you Contact Apple for support and service.

Best wishes!

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Answer 3

ukstanng Author

Level 1

8 points

Dec 21, 2020 2:47 AM in response to MichelleT18

Hello and thank you for your reply.

I have an 20.1 iMac 27, as far as I understand this option is only available with external displays, so I don't have any such settings to select or deselect.

Kind regards

Andrew

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Answer 4

ukstanng Author

Level 1

8 points

Dec 21, 2020 10:59 AM in response to karina184

Hello and thank you for your interest.

I have just, 20 minutes ago downloaded 11.2 beta together with Safari 14.0.3 to see if the problem may have been fixed. Which it has not. I don't use the developer menu in Safari, so the option is deactivated in my setup.

I hope this helps.

Kind regards

Andrew

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Answer 5

ukstanng Author

Level 1

8 points

Dec 21, 2020 6:00 AM in response to MichelleT18

Sorry it's not solved, clicked that by mistake. Sorry.

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Screen mirrors into two exact halves whilst watching media online using Safari 14.1 - OS 11.1

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