Skip to main content

Deciphering the Mystery of HDCP and HDMI

During a coffee break at a conference last month, I was questioned as to why a Blu-Ray player would not display its content through one of the "image processing" products I was there to demonstrate. That simple question led to a lengthy roundtable discussion on yet another new hurdle in our brave new HD world: HDCP.

All the Acronyms Money Can Buy
HDCP stands for High-Bandwidth Digital Content Protection, an industry-wide copy protection scheme that prevents the potential interception of digital data between the source (e.g., a Blu-Ray player) and the target display (e.g., an HDCP compliant display or monitor).

The term HDMI (High-Definition Multimedia Interface) plays directly into this discussion, because it seems to be the connector of choice for the new "HD-ready" consumer products - including Blu-Ray, HD DVD and game systems. The HDMI connector itself is multi-purpose, enabling the transport of digital video, audio, and control protocols.

In the consumer market, this means that "everything" can be sent down one cable from the DVD player to the monitor. In the professional video world, the digital video signal can be converted from the HDMI connector to a standard DVI-D connector by means of a simple adapter, but the adapter only changes the cable type - not the signal itself. If the signal is originally encoded with HDCP via the HDMI cable, the signal will still have HDCP encoding on the DVI cable.

Let's Shake Hands
That is where the "compliance" issue comes into play. Even if you change cable types, a signal originally encoded with HDCP (e.g., on Blu-Ray) retains that encoding. As part of licensing agreement with equipment manufactures, the HDCP protocol requires that any device in the signal path must be HDCP compliant. If compliance is not established, a picture will not be displayed.

The HDCP format (as designed by Intel(r)) uses an "authentication and key exchange" procedure to accomplish its copy protection scheme. In layman's terms, it's a "handshake" between the device and the target display.

In practical terms, the Blu-Ray player must establish that it is connected to an HDCP compliant device before it allows that device to enable the flow of vide. In the professional world, this means that the complete video chain (e.g., source > seamless switcher > projector) must be HDCP compliant. If any portion of that chain doesn't feel like shaking hands - the entire chain goes black.

HDCP Caveats
All the usual suspects in the Pro A/V market are now developing products that embrace HDCP compliance. Yet the responsibility still falls upon the system designers and technicians to ensure that if HDCP material is used in a presentation, all components in the video chain are HDCP compliant.

Following are a few additional useful notes about HDCP compliance:

-When a seamless switcher that is part of an HDCP chain outputs a digital signal (DVI and HDMI), the switcher disables its analog, SDI and HD-SDI outputs - in order to prevent unauthorized recording of the "protected" content.

-When a non-HDCP compliant analog device is connected to an HDCP player, the resolution of the HD output is dropped (down-sampled) from 1920 x 1080 to 960 x 540 - in order to produce an image that is less-than-adequate for HD copying.

-The Windows(r) Vista(r) operating system is including HDCP compliance in their graphics card drivers and supported monitors, which in turn impacts HD DVD playout from a PC. For example, this means that you can't take your HD DVD content and play it out to an analog (VGA) monitor.