HDCP, short for High bandwidth Digital Content Protection, is a form of encryption used on HDMI connections. It scrambles the video and audio signal between a source, such as a streaming box or Blu ray player, and a display, so that the content cannot easily be intercepted and copied along the way. Every device in the chain, including any AV receiver or switch in between, has to support HDCP for the picture to appear at all.
In everyday use, HDCP mostly stays invisible, but it becomes noticeable when it fails. A black screen, flickering image or an on screen error message when starting a streaming app or a protected disc is often caused by an HDCP mismatch somewhere in the chain, for example an older AV receiver that does not support the version required by a newer 4K source. Updating firmware, connecting the source directly to the TV, or replacing an outdated HDMI splitter or switch usually resolves it.
When buying an AV receiver or an HDMI switch to sit between a source and the television, it is worth checking that it supports the current HDCP version so it does not become the weak link. See our guide to HDMI 2.1 for more on how modern HDMI connections work.
