virtualbox.org

I am running a Windows 10 64bit guest using VirtualBox 5.02 on a Windows 8.1 64bit host. I have installed the latest expansion pack and guest additions and have 2d and 3d acceleration enabled. I have a 4K monitor connected to my host running at 4K UHD 3840x2160@30HZ. However when I auto-size the guest in full screen and view the display properties the maximum resolution is 2560x1440. My host does not have a DisplayPort video output and due to this limitation I can only run 4K at 30HZ over HDMI. In the guest if I view the display properties of the display adapter it is locked to 60HZ which may be part of the problem. Does anyone have any idea on how I can get 4K running in my Windows 10 guest?

After further investigation it does appear Virtualbox is filtering the supported host resolutions by the fixed 60hz refresh rate value:

I expect it is Windows which shows you a filtered list, not VirtualBox.

I followed the instructions in this post and in the guest VM I manually specified the resolution using the guest addition VBoxControl.exe command. Setting the VM custom video mode from the host using VBoxManage command had no effect. After restarting the VM I visually confirmed the resolution was set to 4K UHD.

VBoxControl.exe addcustommode 3840 2160 32
VBoxControl.exe setvidmode 3840 2160 32 1

When I use "VBoxControl.exe listcustommodes" or "VBoxControl.exe addcustommode 3840 2160 32" at my windows 10 guest, I always got the error "VBoxControl.exe: error: Error opening video registry key!".

Here's my configuration:
Host: windows 10 + Intel UHD graphics 630 (integrated within Intel CPU, supporting 3820x2160 at 30Hz)
Guest: windows 10
VirtualBox: 5.2.20

BTW, I did use "With the guest running open a 'cmd' window as administrator."

I searched the internet and this Virtualbox forum and did not found any clue related to "error opening video registry key". Does anyone know how to solve this issue? Thanks.

I figured out the solution. That is, I have to add a custom video display at the host instead of the guest VM.

Here's the steps:
1. at the host (not the guest), open a 'cmd' window as administrator.
2. go to VBox Addtion directory (e.g. C:\Program Files\Oracle\VirtualBox)
3. run the command
.\VBoxManage.exe setextradata "your-VM-name" CustomVideoMode1 3840x2160x32
4. start your VM
5. at the VM, use HOME+F to switch to the full screen mode which is 4k at my display monitor.

Note: at the VM, when I ran "VBoxControl.exe listcustommodes", I still got the same error "Error opening video registry key!".