Product Documentation

Optimize graphics and multimedia delivery

Jun 13, 2013

XenDesktop provides a superior graphics and video experience for most users by default, with no configuration required.

  • HDX automatically selects the best delivery method based on the client, platform, application, and network bandwidth, and then self-tunes based on changing conditions.
  • HDX optimizes the performance of 2D and 3D graphics and video.
  • HDX delivers a Windows Aero experience to virtual desktop users on any client.
  • HDX enables user devices to stream multimedia files directly from the source provider on the Internet or Intranet, rather than through the host server. If the requirements for this client-side content fetching are not met, media delivery falls back to Windows Media redirection to play media run-time files on user devices rather than the host server. In most cases, no adjustments to the Windows Media feature policies are needed.

Reduce the bandwidth needed for Windows desktops

By default, XenDesktop delivers a highly responsive Windows Aero or Windows 8 desktop experience to virtual desktops accessed from Windows user devices. To do that, XenDesktop leverages the graphics processing unit (GPU) or integrated graphics processor (IGP) on supported Windows user devices for local DirectX graphics rendering. This feature, referred to as desktop composition redirection, maintains high scalability on the server.

For detailed information, see What to do with all these choices in

Important: For non-Windows clients or when desktop composition redirection is not available, HDX processes graphics on the server, compresses the bitmap image, and sends it over the network to the client. Aero themes are supported, but are not required.

Users of the latest Citrix Receiver releases will notice improved performance for server-rendered video.

To reduce the bandwidth required in user sessions, consider adjustments to the following policy settings. Keep in mind that adjustments to these settings can reduce the quality of the user experience.

  • Desktop Composition Redirection – Applies only to Windows Desktop OS machines accessed from Windows user devices and applies only to the composition of the Windows desktop. Application windows are rendered on the server unless the Citrix policy setting Allow local app access is Allowed.
  • Desktop Composition Redirection graphics quality – Uses high-quality graphics for desktop composition unless seamless applications or Local App Access are enabled. To reduce bandwidth requirements, lower the graphics quality.
  • Dynamic windows preview – Controls the display of seamless windows to provide the following preview options to virtual desktop users.
    Windows Aero preview option Description
    Taskbar Preview When the user hovers over a window's taskbar icon, an image of that window appears above the taskbar.
    Windows Peek When the user hovers over a taskbar preview image, a full-sized image of the window appears on the screen.
    Flip When the user presses ALT+TAB, small preview icons are shown for each open window.
    Flip 3D When the user presses TAB+Windows logo key, large images of the open windows cascade across the screen.

    To reduce bandwidth requirements, disable this policy setting.

Improve the image quality sent to user devices

The following Visual Display policy settings control the quality of images sent from virtual desktops to user devices.
  • Visual quality – Controls the visual quality of images displayed on the user device. By default, the value is set to Medium. To ensure lossy data is never sent to the user device, choose Always lossless. To base whether lossy or lossless images are sent based on network activity levels, choose Build to lossless.
  • Target frame rate – Specifies the maximum number of frames per second that are sent from the virtual desktop to the user device. The default is 30 frames per second. In many circumstances, you can improve the user experience by specifying a higher value.

    If user devices, such as thin clients, have slow CPUs, specify a lower value to improve the user experience.

    If server scalability is an issue, specify a lower value. If server CPU utilization stays at or near 100%, consider adding an additional vCPU.

  • Display memory limit – Specifies the maximum video buffer size for the session in kilobytes. The default is 32768 KB. For connections requiring more color depth and higher resolution, increase the limit. Calculate the maximum memory required using this equation:

    (color depth in bits per pixel / 8) * (vertical resolution in pixels) * (horizontal resolution in pixels) = memory required in bytes

    For example, if the color depth is 32, the vertical resolution is 600, and the horizontal resolution is 800, then the maximum memory required is (32 bpp / 8) * (600 pixels) * (800 pixels) = 1920000 bytes, so you would set the Display memory limit to 1920 KB.

    Color depths other than 32-bit are available only if the Legacy graphics mode policy is enabled.

Improve video conference performance

To improve bandwidth efficiency and latency tolerance during video conferencing in a XenDesktop session, XenDesktop uses HDX webcam video compression for webcams by default. HDX webcam video compression streams webcam traffic over a dedicated multimedia virtual channel. HDX webcam video compression uses significantly less bandwidth compared to the isochronous HDX Plug-n-Play support and works well over WAN connections.

However, Receiver users can override the default behavior by choosing the Desktop Viewer Mic & Webcam setting Don't use my microphone or webcam. To prevent users from switching from HDX webcam video compression, disable USB device redirection through the policy settings under ICA > USB Devices.

Note: HDX webcam video compression is enabled by default on Receiver for Windows but must be configured on Receiver for Linux. For more information, refer to the Receiver documentation in eDocs.

HDX webcam video compression requires that the following policy settings are enabled. All of these settings are enabled by default.

  • Client audio redirection
  • Client microphone redirection
  • Multimedia conferencing
  • Windows Media Redirection

To force software compression over low bandwidth networks

If a webcam supports hardware encoding, HDX video compression uses the hardware encoding by default. Hardware encoding uses additional bandwidth and is not suitable for a low bandwidth network.

Caution: Editing the Registry incorrectly can cause serious problems that may require you to reinstall your operating system. Citrix cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk. Be sure to back up the registry before you edit it.

To force software compression, add the following DWORD key value to the registry key HKCU\Software\Citrix\HdxRealTime: DeepCompress_ForceSWEncode=1.

Choose server scalability over user experience

For deployments where server scalability is of greater concern than user experience, you can use the legacy graphics system by adding the Legacy graphics mode setting to a policy and configuring the individual legacy graphics policy settings. Use of the legacy graphics system particularly impacts the user experience over WAN and mobile connections.