What is up with HDCP?
by David McCauley
HDCP stands for High-Bandwidth Digital Content Protection, developed by Intel Corporation to prevent copying of digital audio and video content as it travels from the video source to the display. This means that HDCP-encrypted content will not play on unauthorized devices, or devices modified to copy HDCP content, and is meant as a means to prevent copyright infringement. It was intended for the consumer based products where illegally copying movies is rampant. Most consumer equipment is set up to make the ‘handshake’ needed to keep content safe while being able to play it on local playback sources only.
HDCP uses three systems; HDCP authentication, data encryption and key revocation that stops compromised or cloned devices from receiving data.
Products compatible with the HDCP such as DVD players, satellite and cable HDTV set-top-boxes, as well as some Macs and PCs, require a secure connection to an HDCP-compliant display before it will allow content to play on those individual devices. More and more manufacturers are employing HDCP in their equipment and that makes it harder for people in the professional world that want to integrate video from computers and other devices whose outputs are now becoming HDCP controlled content.
How does HDCP work?
In a nutshell, an HDCP-compliant device will ask the display device (or other devices in the signal chain) if they are also HDCP-compliant. They do this via transmitting a unique set of forty 56-bit keys to the receiving device or devices. If they are also HDCP-capable, the devices will recognize each other; the sending device will then permit the receiving device to accept the video send and display it at full HD capability.
HDCP devices generally fall into three categories; source, sink and repeater.
The source device is the one that sends the content to be displayed, for example a Blu-Ray, DVD player, or Computer. Source devices usually have an HDCP/HDMI transmitter. Typically HDCP is incorporated with DVI, HDMI, and Display Port / Thunderbolt compatible devices.
The sink device renders content for display so it can be viewed. This includes TVs and digital projectors, for example. Sink devices can have multiple HDCP/HDMI receivers for multiple source connections.
A repeater moves content between source and sink, accepting and decrypting content from the source, before re-encrypting and re-transmitting the data through the signal chain, most commonly to the sink device, but sometimes to another repeater. Repeaters can be switchers or scalers, distribution amplifiers and signal splitters. Repeaters have both HDMI inputs and outputs, and can send content to multiple devices.
How does this affect HoW?
First of all, depending on how professional your video set up is at your church, you need to understand that a lot of the connections that we use today were not designed for professional or even semi-professional use. In the professional world you would use HDSDI for the transfer of video, audio and timecode. But now that we have crossed into using consumer grade equipment and trying to incorporate it into professional systems, it can cause some issues.
If your system has an HDCP device, like a Blu-Ray for example, that you use for sharing small video snippets from movies, TV, etc., you will not be able to do this unless all the other devices in your signal chain are also HDCP compliant. For example, if you plan to incorporate scenes from the recent “Son of God” movie from your HDCP-compliant Blu-Ray device, through a video switcher/scaler to your projector and onto the screen, both your switcher/scaler and your projector must also be HDCP-compliant or the video will either not play at all, or will play in a much lower-quality resolution than the source. These Switcher/Scaler systems that are HDCP compliant can be found, but are limited to display type systems only. If you are looking for a switcher that runs HDSDI and is more of a professional broadcast level switcher you will have issues with anything that has HDCP. (Even if the switcher has HDMI inputs they still might not be HDCP compatible).
Other products affected by HDCP are scalers, switchers, video over Cat5 transmitters and receivers and splitters (distribution amps). While these devices do no authentication for key exchange, they must be able to transmit the presence of HDCP if the video is handled (processed) in any way. Due to the different formats of digital connections, occasional inability for proper communications may result in loss of interoperability. The newer format, HDMI was designed to be backwards compatible with DVI and in most instances, the two signal types are easily adaptable, but older devices may not always work well with in-line devices like scalers or switchers.
According to a recent white paper from Kramer Electronics titled ‘The Challenges of Interfacing HDMI in the World of Professional AV’, there are some issues to consider when connecting HDCP content between source and sinks. As it stands now, when linking between a source and sink via a distribution amplifier or matrix switcher, “the source needs to decipher a different set of keys for each connected display, and if any key is corrupted, no signal will pass to any connected display, even if the remaining displays are transmitting valid keys.” For a House of Worship, this could mean that content will not go to your projector, or won’t stream over the internet, or run on your LED walls or digital signage, or anywhere else you want it to if even one of the display devices connecting through the repeater to the source is not HDCP compliant.
Kramer’s solution to this problem is to make all distribution amplifiers and matrix switchers a sink and source device, instead of a repeater. This means that all source content would be recognized by the switcher or distribution amplifier, which would then turn around and transmit the content to the sink devices further down the signal chain as a source device instead of as a repeater. This would allow content to go out to multiple displays that are HDCP-compliant and not display content on non-compliant devices, without causing problems within your signal chain. Problems with repeaters are eliminated, and multiple sources can now be connected as easily as multiple displays.
Regardless of what happens in the future, HDCP is here to stay – so be aware. More and more computers and other payback hardware that we take for granted are now coming to market with HDCP on the outputs no matter what the content. You don’t want to be introducing new HDCP-compliant products to your current signal chain if the rest of the pieces in that chain are not HDCP-compliant themselves. Even one ‘bad apple’ – or in this case, a non-compliant piece of equipment – can prevent your video from transmitting between source and display, leaving your video production team with no way to fix the problem, short of never using equipment or content that has, or making everything HDCP-compliant and removing the devices that aren’t.
Download ‘The Challenges Of Interfacing HDMI In The World Of Professional Av’ from Kramer Electronics at www.kramerus.com/downloads/white-papers/hdmi_challenges_whitepaper_3.pdf
David McCauley is a consultant with CDS Group.