HDCP, COPY PROTECTION AND THE LAW
Broadcasters, streamers and filmmakers don’t want people pirating their content. One tool to prevent that is High-bandwidth Digital Content Protection (HDCP). HDCP is present in DVI, DisplayPort and HDMI connections, and if all your devices and their cables are not HDCP-compliant content may not play in 4K, or at all. If you encounter an HDCP error on a new Apple TV it means that something between your Apple TV and your TV or projector isn’t compliant: most likely the connecting cable.
In the UK and US it’s legal to make a backup copy of lawfully purchased media for personal use, but illegal to bypass what the UK calls ‘technological protection measures’ to make that backup.