OS-level HDR needs to be toggled after starting stream if already enabled

[M-Gilly]

Describe the bug
When starting a stream, HDR will appear to be too bright. If you toggle the HDR setting off and then on in the Windows Display Settings, HDR will appear correctly. This happens on 2021 Apple TV 4K, iPhone 13 Pro Max, and a Sony Android TV (X900H)

Steps to reproduce
Enable HDR in the Windows Display Settings of the host PC. In Moonlight settings, enable HDR. Begin streaming any application, including mstsc. The brightness will be blown out and too bright. Toggle HDR off then back on in the Windows Display Settings. HDR will appear correctly for the entirety of the stream. When you disconnect and reconnect, HDR will be broken again. Moonlight HDR Launcher’s Toggle HDR option also fixes the issue.

Affected games
Affects all games

Other Moonlight clients
iOS and Android

Moonlight settings (please complete the following information)
HDR and HEVC turned on. 4K 60 stream.

Server PC details (please complete the following information)

• OS: Windows 10 and Windows 11
• Moonlight Version: 4.0.0
• GPU: GTX 1080

Other Details
I have an LG 4K HDR Monitor connected to the host. I have a Sony X900H HDR 4K TV attached to the client (it also acts as a client with its Android TV)

[cgutman]

This is a bug in GFE sending incorrect HDR state when OS HDR is enabled when nvstreamer.exe starts.

[M-Gilly]

This is a bug in GFE sending incorrect HDR state when OS HDR is enabled when nvstreamer.exe starts.

Thank you! Is there a setting I can change or is it something that NVIDIA would need to fix?

[cgutman]

Unfortunately it's something NVIDIA would need to fix. I tried to see if I could work around it on the client-side in Moonlight, but it's not just a matter of flipping the client display into HDR mode. The stream we're getting from the PC is in the wrong colorspace (Rec 601 instead of Rec 2020), so the extra color data is already lost by the time it gets to us.

[M-Gilly]

I appreciate the information. For anyone interested, Moonlight HDR Launcher is a workaround if you enable “toggle HDR” on that.