Firstly, LG C2 42" running at 4K @ 120Hz @ RGB 10Bit FULL, with the GPU being an RTX 3090.

MPV Version v0.37.0

My Config:

    ontop
    fullscreen=yes
    d3d11-exclusive-fs=yes

    vo=gpu-next
    gpu-api=d3d11
    hwdec=d3d11va-copy
    video-sync=audio
    gpu-context=d3d11
    fbo-format=rgba16hf

    target-peak=800
    target-contrast=inf
    target-colorspace-hint=yes

HDR Enabled in Windows 11 Pro Build 22631.3085:

VRR (GSync and Freesync Premium) enabled in the Display and NVCP <-- this results in crushed black levels and banding with d3d11va-copy running at 24FPS (even outside the VRR range, so VRR is not even working).

Changing to d3d11va solves the problem. No crushed black levels or banding issues.

DDU uninstall nVidia drivers. Shut down the PC. Turn off GSync and Freesync from the display. Turn the PC on and install NVidia drivers.

Run again with both d3d11va-copy and d3d11va, no problems at all with both. No crushed blacks, and no banding. Everything running smoothly.

Conclusion:

Just enabling VRR causes d3d11va-copy to crush black levels and introduce banding on the LG C2, even when the video playing is outside the VRR range (my range is 40Hz to 120Hz), with the HDR video playing at 24 FPS.

So back to the title, what is the difference between d3d11va and d3d11va-copy that is causing the -copy to break when VRR is enabled.

Not sure if this is an MPV issue, or a display issue that is causing the problem. So didn't know where to report (windows issue, mpv issue, elsewhere) so I'd rather just ask the question.