Why does VNC shadowing show a black screen on RX-series thin clients?

Why does VNC shadowing show a black screen on RX-series thin clients?

The Raspberry Pi-based devices (RX300, RX-RDP, RX-RDP+, RX420(RDP), and RX440(RDP)) use a hardware-based H.264 decoder to accelerate the video decoding in RDP, AVD, and Windows 365 sessions. However, the output of that hardware H.264 decoder is inaccessible to the VNC server, which results in shadowing of the device only showing a black screen. To enable shadowing of RDP, AVD, and Windows 365 sessions, H.264 support needs to be disabled. This can be done by specifying the following custom parameters:

  1. For the RDP sessions on RX420(RDP) and RX440(RDP) devices, use this custom parameter /noh264
  2. For the RDP session on RX300, RX-RDP and RX-RDP+ devices, use this custom parameter /novcast
  3. For the AVD (and Windows 365) sessions, use this custom parameter h.264 support=b:false

Screen shadowing of devices running RDP or AVD sessions will then be possible, however, the session performance may be slightly degraded. We recommend only temporarily disabling the H.264 support for the duration of the troubleshooting session, and re-enabling it for normal operation.


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