[vbox-dev] Monitor count limitations

Vitali Pelenjow Vitali.Pelenjow at oracle.com
Thu Sep 4 08:49:24 GMT 2014

Good to know that it works!


Rūdolfs Bundulis wrote:
> Hi Vitali,
> no it does not. And I just found the issue, the H264 encoder was 
> actually stalling after the 1280x720 resize on all 25 monitors and 
> since I was checking this from home and I did not have access to the 
> actual wall, I did not see that. I fixed it an yeah, now I got all 25 
> to resize to full hd, after they were all resized to 1280x720. So with 
> XPDM the VRAM amount is sufficient for my needs. Seems that I'll have 
> to stack multiple GPU's or combine GPU/CPU encdoing to actually be 
> able to pull this amount of pixels off at 25fps. Sorry for that, I 
> hope I didn't take too much of your time with the verifications done 
> on your side  and thank you both (you and Klaus) for the info - the 
> XPDM thing was very important, now I can run all the 5x5 wall with 
> full hd.
> Best Regards,
> Rudolfs Bundulis
> 2014-09-04 10:43 GMT+03:00 Vitali Pelenjow <Vitali.Pelenjow at oracle.com 
> <mailto:Vitali.Pelenjow at oracle.com>>:
>     Does the VM have 2d acceleration enabled (in the VM settings)?
>     Which version of VBox/guest addidions do you use?
>     Please also send me VBox.log of the VM with 25 monitors.
>     And the VM xml config file (VMNAME.vbox).
>     I tried with current VBox trunk. Used one of existing Win7 32 bit
>     VMs with XPDM driver.
>     I edited the .vbox xml config to set 256MB VRAM and 24 monitors.
>     Then started the VM with VBoxHeadless and on the host executed
>     a batch script with VBoxManage controlvm setvideomodehint for each
>     monitor.
>     Then connected to the VMs first monitor with a RDP client and
>     checked that
>     Display Properties in the guest show all 24 monitors at 1920x1200.
>     Vitali
>     Rūdolfs Bundulis wrote:
>         >I wonder why monitors in your guest resize to 1280x720.
>         >Did you allow all modes in IFramebuffer::VideoModeSupported?
>         >Can you run 1 monitor at 1920x1200?
>         >How do you resize the guest monitors: from the guest or using
>         VBoxManage
>         >controlvm setvideomodehint?
>         And I try to force the desired resolution like this:
>         for (unsigned short nMonitorIndex = 0; nMonitorIndex <
>         m_nMonitorCount; ++nMonitorIndex)
>         {
>         // Set full hd for all the screens
>         CHECK_HRESULT(m_pDisplay->SetVideoModeHint(nMonitorIndex,
>         true, false, 0, 0, 1920, 1080, 32));
>         }
>         One monitor runs fine, 7 also work, I didn't have time now to
>         find exact boundary but I will do it. Bascially in all the
>         configuriation the VirtualBox logs shows the hint for
>         1920x1080 but a bit later just resizes to 1280x720 and does
>         not even try that. I'll mail you the source and logs directly,
>         thanks for the help.

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