If connecting the USB-CEC Adapter in-line between your PC and TV causes white pixel noise, a flickering image, or audio distortion — and removing the adapter resolves the issue — this is caused by outdated adapter firmware interfering with signal integrity. Updating to firmware V12 resolves it.

Symptom

• Random white pixels scattered across the screen when the CEC adapter is connected in-line
• Image flickering or instability that disappears when the adapter is bypassed
• Audio distortion or dropout that correlates with the adapter being in the signal path
• The issue is consistent regardless of source device or content

Cause

This is a known issue with older firmware versions — particularly firmware v4. The older firmware does not handle the HDMI signal path cleanly, causing interference when the adapter is used in-line. This was resolved in firmware V12.

Fix — Update to Firmware V12

1. Download the latest libCEC installer from github.com/Pulse-Eight/libcec/releases. The firmware update tool is included.
2. Disconnect all USB-CEC Adapters except the one being updated.
3. Connect an HDMI cable to the adapter during the update.
4. Run the firmware update tool as Administrator and update to firmware V12.
5. Reconnect any remaining adapters and update each one individually.

After updating, reconnect the adapter in-line and confirm the visual noise has resolved.

If Visual Noise Persists After Firmware Update

In rare cases, the adapter hardware itself may be causing signal integrity issues. If updating to V12 does not resolve the problem, try the non-inline connection method — use the adapter for CEC control only rather than passing the video signal through it:

• Connect your PC to the TV via HDMI directly (video and audio — bypassing the adapter entirely)
• Connect the CEC adapter to a second HDMI port on the TV via a short HDMI cable (under 2m)
• Connect the adapter to the PC via USB as normal

The TV will see CEC traffic from the adapter on the second port and respond to commands. Your video signal is not affected. See USB-CEC Adapter 4K Resolution for more on this configuration.

Related Articles

• Upgrading the Firmware of the CEC Adapter
• CEC Adapter — Firmware Update Hangs or Won't Complete
• USB-CEC Adapter 4K Resolution