08.05.17

CEDIA: Link quality is crucial for HDCP 2.2 stability

David Meyer headshot

An issue was raised recently on the CEDIA Community Forum concerning 4K content, which either doesn’t work or flashes on and off when used through an HDMI splitter, questioning whether HDCP 2.2 is stable and governed by a standard. David Meyer, CEDIA Director of Technical Curriculum, finds out.

HDCP 2.2 should be very stable and seamless, but is reliant on a quality link to ensure things go smoothly. Kind of sounds obvious, huh? HDCP 2.2 uses tougher security and a different continuous check system throughout transmission than was used in HDCP 1.x (version 1.3 or 1.4), making link quality even more important. But since you want to push at least double the bandwidth down the pipe for 4K, the use of high quality connectivity is already considered a best practice.

As for whether HDCP 2.2 is officially specified, the answer is yes. There are actually seven separate specifications for HDCP 2.2 - one catch-all version, plus six others for specific interfaces, including HDMI. Contrary to popular belief, HDCP 2.2 interfaces seamlessly with HDCP 1.x, the older copy protection system used for 1080p and below.

Every link between devices in a system authenticates separately. For example, an Ultra HD Blu-ray player that is HDCP 2.2 connected to an AV receiver will always try to authenticate using HDCP 2.2. If it fails, perhaps because the AV receiver doesn’t support 2.2, it will fall back to HDCP 1.x to establish a successful link. Most 4K content is flagged with a “Stream Type” bit. Type 1 requires mandatory HDCP 2.2 and will not pass over an HDCP 1.x link, whereas Type 0 can pass over any version of HDCP. All 1080p content is Type 0.

The output side of the AV receiver will establish a separate authenticated link with the next device downstream, resulting in either HDCP 2.2 or 1.x depending on the two devices’ capabilities. However, the source continues to manage the content at all times. 

Regarding the challenge of 4K content failing, or appearing unstable or intermittent, this really comes down to link integrity or HDCP 2.2 protocol issues. Link integrity means the whole signal path, including device circuits and cabling, with just as much importance on the high speed AV channels as on the “slow” auxiliaries. 4K needs a lot more bandwidth than 1080p - two to four times more in fact. Keep in mind that losses can be cumulative. The longer the HDMI cables, and more hops and complexity in the system, the more chance of things going wrong and the harder the issue becomes to diagnose. The DDC wires in HDMI carry the EDID (Extended Display Identification Data) from TV to source, but they also handle all the HDCP authentication as well, and once established are responsible for the “Link Integrity Check” to monitor the successful decryption of content at the display. Simply put: Bad link = shaky result.

www.cedia.co.uk

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