Not Authenticated
Not Authenticated
Authenticated
Authenticated
Authenticated
Authenticated
Authenticated Not Authenticated
FIGURE 2: Results when copyrighted content is routed to HDCP compliant and non-HDCP compliant devices.
October/November/December 2019 I 9
High-bandwidth Digital Content Protection (HDCP)
HDCP enforces program content copyright protection by
encrypting the signal. To view the content, a successful
authentication handshake and encryption key transfer
between the source and the sink is required. HDCP restricts
what the end user can do with protected content by limit-
ing the number of simultaneous displays, disallowing
recording or copying and disabling analog outputs. HDCP
has evolved from Version 1.0 for DVI to the current
Version 2.2 for 4K video. Since Version 2.0, HDCP has
been interface independent, making it ubiquitous on all
current AV interfaces: DVI, HDMI, USB-C and DisplayPort.
HDCP can be problematic in complex AV systems.
The HDCP handshake introduces a noticeable delay,
which can be bothersome in AV systems containing video
switchers. Switcher manufacturers have designed methods
for eliminating switching delays by maintaining continuous
HDCP authentication between switcher inputs and
outputs, eliminating reauthentication during switching.
Another issue is that HDCP specifications have evolved
and newer sources may not work with older downstream
equipment. The best rule is to ensure everything in the
path conforms to the highest level of HDCP protection
that will be encountered. For 4K video, that means HDCP
2.2. If this rule is overlooked, it is possible the source will
not output the protected video content or may downgrade
it to 1080p; even if downstream devices perform
successful HDCP authentication at a lower level of HDCP
protection, the results will not be consistent. If a downstream
device has no HDCP capability at all, there will
likely be seen an error message or black or noise on
the display.
As an aid to troubleshooting, some professional
video switchers respond to such noncompliant HDCP
situations by outputting green screen video to the
display to indicate that at least the display is active
and receiving a signal. HDCP is backward compatible.
For example, content protected by HDCP 1.4 will be
displayed on an HDCP 2.2 display. If the content is not
copy-protected, HDCP usually does not come into play.
Figure 2 illustrates an example of how HDCP is handled
under a common scenario.
PC with
DVI output
HDCP Display
HDCP Display
HDCP Display
Non-HDCP
Display
Digital Matrix
Switcher
Matrix Input Matrix Output
PC with
DVI output
4K Blu-ray
with HDMI
4K Blu-ray
with HDMI
• Switcher connects HDCP
protected video content
from Blu-ray to displays.
• Authenticated HDCP
displays show the content.
• Non-HDCP display shows
green screen generated
by switcher, indicating that
switcher output and display
are active, but copyrighted
content cannot be shown
on this display. For the
green screen, there are tools
for troubleshooting HDCP
noncompliance issues.