[Resolved] Remote video content flickers on Windows client with dual fullscreen streams — disabling client-side MPO fixed it

[li-xisheng]

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Question

Body

I’m posting this as a troubleshooting note in case someone else runs into a similar issue.

Summary

When using two remote streaming windows on a Windows client, the video content inside the remote window flickered, while the window border, title bar, taskbar, and desktop did not flicker.

This happened not only with Sunshine/Moonlight, but also with another remote-control application, so it does not seem to be a Sunshine-specific host-side issue.

In my case, disabling Windows MPO (Multiplane Overlay) on the client PC fixed the problem.

Environment

Client PC:

• Windows
• Dual-monitor setup
• Client display 1: laptop internal display, 1920x1080, 60.001 Hz, Intel Iris Xe
• Client display 2: Dell P2723DE, portrait 1440x2560, 59.951 Hz, Intel Iris Xe

Host PC:

• Host display 1: landscape monitor, 3840x2160, 120 Hz, RTX 4090
• Host display 2: portrait monitor, 2160x3840, 60 Hz
• Two Sunshine instances, one for each host display
• Two Moonlight connections on the client, one for each Sunshine instance

Symptoms

• One remote window in fullscreen was usually fine.
• Two remote windows in fullscreen at the same time caused flickering.
• The flicker happened only inside the remote video content.
• The window border, title bar, taskbar, and desktop did not flicker.
• The same type of flicker also happened in another remote-control application, not only Moonlight.

Fix

On the client PC, run PowerShell as Administrator:

reg add "HKLM\SOFTWARE\Microsoft\Windows\Dwm" /v OverlayTestMode /t REG_DWORD /d 5 /f

Then reboot the client PC.

To restore the default behavior:

reg delete "HKLM\SOFTWARE\Microsoft\Windows\Dwm" /v OverlayTestMode /f

Then reboot again.

To check the current state:

reg query "HKLM\SOFTWARE\Microsoft\Windows\Dwm" /v OverlayTestMode

If it shows OverlayTestMode REG_DWORD 0x5, MPO is currently disabled.

Notes

This appears to be a Windows client-side DWM / MPO / hardware overlay issue rather than a Sunshine host-side capture or encoding issue.

Possible keywords for search:

Moonlight, Sunshine, flicker, remote video flickering, content flickering, border not flickering, dual monitor, portrait monitor, fullscreen, Windows MPO, Multiplane Overlay, DWM, OverlayTestMode.