Blank screen when connecting to big (> 4K) desktop

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    I’d like to report on  a problem that seems to be related to the video codecs, when trying to connect to a server with a very big desktop configuration. The codec(s) fail to encode the surface and the client receives sometimes a blank screen, sometimes a fully green screen. Meanwhile, mouse controls do actually work. Testing the same connection with a smaller screen configuration, fixes the problem.

    The exact configuration is composed of 3 FullHD (1920×1080) screen and one 4K screen, forming a virtual desktop size of 5760×4040. The screens are not totally adjacent between them, but set in a specific layout as shown in the attached image (screenshot from the ‘arandr’ program).

    System information for both systems Server and Client:

    • NoMachine 5.0.53 Free
    • Trying to connect to a physical desktop which is already running in the server
    • Ubuntu 14.04 (“Trusty”), minimal server installation, fully updated
    • Openbox window manager on server, KDE on client
    • AMD FirePro W9000 graphics card, with proprietary driver fglrx version 14.502.1040 [1]
    • Enabled x264 codec as per the documentation ( and (

    Note [1]: the steps described here ( were followed, but they break OpenGL applications in the server, because the library present in /usr/lib/x86_64-linux-gnu/mesa are not the “good” ones. Actualy, the fglrx driver correctly installs its own library at /usr/lib/fglrx/, and the corresponding symbolic link is created at /usr/lib/

    The connection works successfully when only 1xFullHD and 1x4K screens are connected. However after connecting the other 2xFullHD, the problem comes back, probably caused by this error line in ‘session’ file:

    x264 [error]: Input picture width (5760) is greater than stride (0)

    Folders ‘~/.nx‘ and ‘/usr/NX/var/log‘ where cleared before rebooting and performing a connection test, and their contents are also attached to this message.

    All seems to be just a matter of maximum resolution allowed by either the x264 of the VP8 codecs, however if there are any other tests that could prove useful for studying this problem, I will be absolutely able to do it.

    Best regards



    thank you for reporting and for the very accurate analysis!

    We have reproduced this issue in our labs and opened a Trouble Report to track it:


    Thank you very much for your fast reply

    I’d like to comment on a related topic: is it possible to just stream from one portion of the source desktop? Eg. in my setup, most of the time I just want to have remote access to the specific region corresponding to one of the FullHD screens. This would mean a practical surface of 1920×1080, which imposes much lower encoding and performance requirements on the server side.

    I know the options related to the resolution and the screen selection on the client side, but I haven’t been able to find any document which states that any of those will instruct the server to actually encode only a specific sub-region of the whole remote desktop.


    It is not possible at the moment, but it is something we are working on. It will be possible to encode a single monitor or even a portion of the remote screen selected by the user.


    This topic is now closed. Please use the notify me alert to know when a fix is available.

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