Product Documentation

Known issues

Dec 21, 2016

General known issues


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.

  • After the called party accepts a video call as audio-only, the caller cannot add a third participant to turn this into a conference call. [LOP-1504]

    Workaround: The called party can add the third participant, after which all conferencing capabilities are available. 
  • In some cases on Linux, the self-view picture might display only a corner portion of the full video. [#LOP-1814

    Workaround: Resize the video conversation window.

  • On some low-end thin clients with AMD chipsets, outgoing video in conference calls cannot be decoded by other conference participants (they see a black rectangle instead of actual video). [#LOP-1817]

    Old versions of graphics card drivers might impact the stability of the RealTime Optimization Pack. H.264 hardware encoding and decoding on Intel and AMD chipsets works most reliably with the latest versions of graphics drivers available from the endpoint or chipset vendors. RealTime Optimization Pack might automatically disable these features if an unsupported driver version is detected.

    Workaround: Update the display adapter driver or disable H.264 hardware acceleration by using the following registry key:

  • In multiparty conferences where some participants support only the real time video codec (for example, Lync 2010 or Lync for Mac), other participants might sometimes see a black rectangle instead of the incoming view. [#LOP-1665]
  • When using the unsupported combination of RealTime Media Engine 2.1 on a Windows, Linux, or Mac endpoint and RealTime Connector 2.0 on the server, the RealTime Optimization Pack takes approximately two minutes before it goes into fallback mode. [#LOP-1174]

    Workaround: Upgrade RTC to 2.1, or temporarily uninstall RTME 2.1 and install RTME 2.0 until RealTime Connector can be upgraded.

  • If a user on Mac OS X changes the dock UI setting while Skype for Business is running, current and future calls do not display local or remote video [#LOP-1062]

    Workaround: Restart Skype for Business.

  • The number of fallback sessions per XenApp server is currently limited to 10. Fallback to server-side media processing occurs when there is no RealTime Media Engine on the user device. When the limit of 10 simultaneous fallback sessions is reached on a XenApp server, the next user without a RealTime Media Engine observes the notification area icon change to show a red exclamation mark and the status is Not Connected. If this issue is problematic in your environment, contact Citrix Technical Support. [#LC6361]
  • Ignore the roundtrip time (RTT) values shown in the Quality of Experience (QoE) reports for RealTime Optimization Pack calls, as they are not calculated correctly. [#LC6084]

  • Intermittent call disconnects were observed with some combinations of Cisco Video Communication Server (VCS) gateway, ISP provided NAT, and Microsoft Edge Server. If you observe this issue, supply log files to Citrix Technical Support. [#LC6342]
  • On team calls with Simultaneous Ringing set, a call disconnect might occur when someone else picks up the call. If you observe this issue, supply log files to Citrix Technical Support. [#LC6548]
  • An interoperability issue with Cisco VCS gateways was observed when encryption is forced on, resulting in a black video region. [#LC6614]

    Workaround: Enable H.264 Advanced Video Coding (AVC)on the Cisco VCS. 
  • We have not qualified the Polycom RealPresence Trio as Citrix Ready, and it manifests an interoperability issue with call controls. [LC6565]
  • If a caller plugs in another human interface device (HID) during an active call, the call might drop. [#LOP-1377]

  • Skype for Business might crash at startup after RealTime Connector is installed. Workaround:  Restart Skype for Business.  [#608171]

  • Some headset devices (for example, Polycom and Plantronics) are mistaken for speaker phone or handset devices.  Workaround: Restart Skype for Business [#605349]

  • If Citrix Receiver for Mac 12.0 is on the endpoint device and a Human Interface Device (HID) is removed after Skype for Business and RealTime Optimization Pack are running, the RealTime Media Engine might crash. Workaround: Upgrade your version of Citrix Receiver for Mac to 12.1. [#612448]

  • Skype for Business might crash when exiting a video conference call or when exiting from the notification area. [#612444, #612115, #610894]

  • Citrix RealTime Optimization Pack, does not appear in the Citrix Receiver for Windows Support Info generated from the Advanced Preferences menu. [#608200, LOP-650]

  • When a public switched telephone network (PSTN) gateway is configured to generate custom ringback tones, the Skype for Business built-in ringback tone might be heard for a short period before the gateway ringback is heard.[# LOP-1243]

  • When fallback mode is set to audio only, and the users in fallback mode participate in a video conference, they might see their own states in the participant list displayed incorrectly as On Hold. Other users are not affected. [#LOP-1175]

HDX RealTime Media Engine known issues

  • The RealTime Media Engine v2.0.5 causes a slideshow effect in conference video calls when interoperating with 2.1.X and 2.2.X. [#LC6665]

    Workaround: Disable H264UC codec:
    Add DWORD DisableH264UC in the registry:[HKEY_CURRENT_USER\Software\Citrix\HDXRTConnector\MediaEngine\CodecSettings]
    The codec is enabled if the value is absent or set to 0, and is disabled if the value is present and set to 1.
  • For Citrix Receiver for Windows versions  4.2 and earlier - Uninstalling the Citrix Receiver, uninstalls HDX Real Time Media Engine. You must reinstall HDX Real Time Media Engine after installing Receiver. For more information, see [#484913]
  • Sometimes, when attempting to install HDX RealTime Media Engine on Windows, a message indicates that there is no available disk space. However, limited space does exist on the Z:/ drive of the terminal. This is a known issue for Microsoft installers and applies to Citrix Receiver as well.
  • During installation or un-installation, it is possible to encounter certain error conditions where the error message string is not localized. [#14530, #93]
  • In Seamless mode, the following issues exist for Full Screen video:
    • Full Screen video appears in letterbox format with the Linux version of the RealTime Media Engine in Seamless mode. [#13564]
    • The Full Screen Control hides behind other apps in a Seamless session in XenApp Seamless mode. [#10731]

Third party issues

  • The Windows 10 Anniversary Update has issues with web cameras and H.264 that might cause unnecessary bitrate adaption problems in RealTime Optimization Pack to RealTime Optimization Pack video calls. The problem is constant video resolution changes on your Windows 10 endpoints. [#LOP-1985]


Add this registry key to the Windows 10 endpoint.

[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows Media Foundation\Platform]

  • RealTime Connector on 64-bit Windows might crash or become unstable if Microsoft .NET Framework 4.6 is installed with default configuration. For possible workarounds, see RyuJIT settings cause managed applications to crash after you install Microsoft .NET Framework 4.6. [#LOP-1278]
  • There might be problem dialing dual tone multi frequency (DTMF) digits using a Jabra Pro 9465 device on a Linux client. Workaround: Use the RealTime Optimization Pack interface to dial the DTMF digits. [#547234]
  • Citrix RealTime Optimization Pack does not support the Plantronics Clarity P340 audio device. [#597048, 603639, 608218]
  • Linux might mistake some audio devices containing buttons for a Human Interface Device (mouse) instead of an audio device. When a user presses a button, Linux interprets it as a mouse button press and prevents the regular mouse from working correctly until the call is terminated.
    Workaround: Configure the Linux X11 graphics subsystem to ignore the devices as sources of user input by creating or modifying a .conf file in the /usr/share/X11/xorg.conf.d directory with the following sections (for example, Jabra, Plantronics, or Sennheiser). [#521088]

Section "InputClass"
Identifier "Jabra"
MatchVendor "Jabra"
Option "Ignore" "True"

Section "InputClass"
Identifier "Plantronics"
MatchVendor "Plantronics"
Option "Ignore" "true"

Section "InputClass"
Identifier "Sennheiser"
MatchVendor "Sennheiser|1395"
Option "Ignore" "true"

  • The microphone volume level of some Linux clients is low.

Workaround: Increase the microphone level using the Linux system volume control.

  • The microphone volume level of the Polycom CX100 speakerphone is very low even at its full level when used with the HP Thin Pro client. [#604219]

Workaround: You can modify the registry key that comes with the HP Thin Pro comes by using the regeditor program on the client, which can be run as root, or from the Registry Editor component of the Profile editor.

These settings limit the range of available settings on the input volume slider.  The RecordScale default value of 100 limits it to 25% of its maximum value for the microphone jack.  Setting RecordScale to the maximum value of 400 allows the slider access to the entire scale.


Value name: RecordScale
Value data: 400 (Default is 100)

Value name: RecordScaleAuto -
Value data: 0 (Default is 1- sets to 100)

1         Sets RecordScale value based on  hardware type.

2         Does not set RecordScale value based on hardware type.

For playback, these controls work the same way as the input volume controls.


Value name: OutputScale
Value data: 400 (Default is 100)

Value name: OutputScaleAuto
Value data: 0 (Default is 1)

  • You might encounter errors with Skype (not Skype for Business) on iOS 9.2. Workaround: Upgrade to iOS 9.3.2 [#LOP-1313]
  • If you have more than one camera connected to an endpoint and you want to use the second camera for videos or video previews, open Tools > Video Device Settings and select the camera and click OK. [#LOP-1397]
  • If Skype (not Skype for Business) fails to connect video from the RealTime Optimization Pack in a video call, you might see a black screen or a still video from the RealTime Optimization Pack user. [#LOP-1295]