HDMI: It’S Not Just Cable Length and the Role EDID and HDCP Encryption Will Play

HDMI: It’s Not Just Cable Length And the role EDID and HDCP encryption will play.

By Rob Carter The promise of the High-Definition Multimedia Interface (HDMI) is great. installation industry, and the design One cable carries uncompressed digital HD video and audio; what’s not to like? doesn’t scale well. Compounding the But mention HDMI to an AV integrator and you’re likely to get an expletive in problem is the fact that digital control response. A quick search of online forums and industry trade pubs will uncover is relatively new to most of the major a slew of HDMI-related complaints, ranging from annoying switching delays AV distribution players, so the learning and screen flashing to complete audio and video failure. curve has been pretty steep. Though much more complex than Two Reasons For Problems analog, HDMI isn’t nearly as compli- There are two primary reasons for HDMI problems: bandwidth and complex- cated as home automation, Ethernet or ity. Uncompressed HD video requires enormous digital bandwidth, which is any of the myriad wireless protocols. notoriously difficult to push down copper wire. Add popular features, such as Companies with experience in these 1080p resolution and Deep Color, and the problem gets worse. Products are fields are in a position to implement cropping up on the market that attempt to address this issue, some of which HDMI in environments that the de- actually work quite well. But the under-discussed issue is the sheer complex- signers hadn’t anticipated. ity of HDMI. Here, we’ll address the need for the HDMI is a full-duplex digital communications interface. HDMI takes ad- move to HDMI and explain the new vantage of its digital nature and adds several communications mechanisms features that HDMI supports. We’ll that are designed to control and encrypt the content automatically. Unfortu- demystify the “handshaking” that oc- nately, the engineers who designed HDMI weren’t thinking about the custom curs between HDMI sources, repeat-

Rob Carter earned a degree in Computer Engineering from Johns Hopkins University, and currently is a firmware developer and HDCP expert at Crestron Electronics, Inc.

78 Sound & Communications www.soundandcommunications.com ers and displays. We’ll also explore the runs the risk of becoming obsolete DK:G*%%IDE7G6C9H6K6>A67A: cause of some common problems seen over the next several years. Now is IDB::I6CNHE:8;DG6CN?D7# in the field. the time for the consumer electronics and custom installation industries to Say Goodbye To Analog embrace the transition. Before we get too involved in the HDMI’s complexity becomes obvi- technical details, there’s an important ous when you compare its cables to question to address: Why do we need those of analog audio and video. Ana- HDMI? As much as a lot of us would log cables typically consist of one to love to stick with tried-and-true analog three wire pairs, depending on the for- distribution, for much of the market, mat, and they simply carry an audio it’s on its way out. Content provid- or video signal. In contrast, the HDMI ers such as television producers and cable consists of 19 wires, which carry movie studios love the fact that HDMI the following digital signals: supports the High-bandwidth Digital • TMDS: The digital audio and vid- Content Protection (HDCP) protocol. eo data is encoded into three Transi- HDCP allows them to encrypt content tion Minimized Differential Signaling while it’s on the wire so it can’t be cop- (TMDS) channels. TMDS is the trans- ied and pirated easily. They’re push- port protocol used by HDMI to reduce ing hard on the consumer electronics transmission problems. Embedded in Full Discount Wholesale industry to move from analog AV to the video data are InfoFrames, which is the premier supplier of HDMI, and they’re getting their way. are data packets that carry informa- Professional Audio, Video, For the unconvinced, here are a few tion about the AV content. The three A/V and Lighting equipment harbingers of analog’s demise: TMDS channels correspond to the to resellers and contractors. • Image Constraint Token: The Blu- three channels of RGB or YCbCr (the ray specification has a built-in time digital equivalent of YPbPr), depend- FDW Offers: bomb that’s yet to go off: the Image ing on the format. Audio and Info- Extensive Inventory Constraint Token (ICT). This disc-spe- Frame data is spread across the three Low Cost Shipping cific flag forces players to downgrade channels during blanking periods in No Minimum Order video on analog outputs to 540p, half the video. These three channels and the 1080i resolution of the current a TMDS clock are carried over four Hundreds of the Top Brands analog maximum. Movie studios are pairs of wires in the cable. Friendly, Experienced Sales Pros waiting for more widespread HDMI Exceptional Customer Service and Blu-ray adoption before shipping Data Display Channel Blind Drop Ship Capability discs that implement this limitation, • DDC: The Data Display Channel and reportedly have decided not to (DDC) is a two-way communications do so until 2010 or 2012.1 interface between the source and the • Content provider support: SkyHD, downstream repeater or display device. a popular European satellite service, Originally, this channel was provided is already shipping HDMI-only set-top to communicate device capability in- boxes. In the United States, the MPAA formation, which is encoded in a struc- is petitioning the FCC for permission to ture known as Extended Display Iden- block certain movies from being trans- tification Data (EDID). HDMI devices mitted on set-top box analog outputs.2 use the EDID to indicate what audio and video formats they support. This Feature Support is discussed in more detail later. The • Feature support: The latest and DDC interface is also used to set up greatest features are supported only and maintain HDCP encryption. by HDMI. The aforementioned 1080p • Hot Plug Detect: The downstream and Deep Color formats, for instance, device, or sink, indicates its presence aren’t available over analog, and they to the source with the Hot Plug De- never will be. Early adopters, the tect (HPD) signal. The sink can toggle bread-and-butter for much of the cus- the Hot Plug Detect signal to reset the tom installation industry, will need to HDMI connection, which resets the move to HDMI. HDCP session and triggers an EDID Any analog distribution system that read. carries commercially created content There are more control signals asso-

September 2008 79 have in different ways. Combining the EDIDs can be a complicated issue, so it’s worth researching how a given switch handles EDIDs before installation. Consider a simple system you might design for a financial services firm. The client has a 1080p Deep Color projector with a surround sound processor in the boardroom and a 720p LCD with integrated speakers at the trading desk. The 1080p projector also supports 720p but, obviously, the cus- Figure 1.

Figure 2. ciated with HDMI, but they are beyond The EDID exists in a memory chip tomer would prefer 1080p when pos- the scope of this article. on the display or AV processing device. sible. How should the switch combine Every HDMI installation consists of The content source reads the EDID the EDIDs? at least one content source, such as a over the DDC interface and analyzes Some devices on the market simply cable box or Blu-ray player, and a sink, it to decide what formats to send. It copy the EDID from the first output, as such as a TV or projector. Most custom is the responsibility of the content depicted in Figure 1. In our scenario, installations will also involve at least source to send only formats that the 1080p Deep Color video and surround- one repeater, which is a device that ac- downstream devices can support. HD sound audio will be sent to the trad- cepts and retransmits HDMI content. players, such as Blu-ray players, must ing desk LCD, which supports neither. Repeaters include simple devices, such include a video scaler to re-scale the At best, this will result in no audio or as switches and distribution amplifiers, video on the disc to match the capa- video and, at worst, in damage to the as well as more feature-rich devices, bilities of the television or projector. LCD display or speakers. such as audio and video processors. Likewise, the source must provide a supported audio format. Smarter Switch EDID In the simplest installations with A slightly smarter switch may take a • EDID: HDMI display and AV pro- one television and an audio proces- “best common” approach and generate cessing devices use the EDID to ad- sor, the EDID protocol works reason- an EDID that advertises formats that vertise their capabilities. For instance, ably well. Multi-room installations, on both rooms support. This scenario is a television may use the EDID to indi- the other hand, quickly can become shown in Figure 2. The merged EDID cate support for the standard HD reso- much more complicated. Several tele- will limit the content to 720p video and lutions plus 1080p and Deep Color. An- visions may be connected to several stereo audio. Now, both rooms support other TV may max out at 720p/1080i sources through one or more HDMI the content, but the client’s lavish resolution. One audio processor may switches. The switches are responsible boardroom isn’t getting the topnotch support Dolby TrueHD, whereas an- for collecting the televisions’ EDIDs content that justifies the expense. Ex- other only supports standard Dolby. and providing one unified EDID to trapolate this scenario to the installa- And most TVs only support basic ste- the source. Neither the HDMI nor the tion with five or 10 rooms, and this reo audio or none at all. All of this in- EDID specifications offers guidance in simplistic solution becomes completely formation is stored in the EDID. this scenario, so different switches be- insufficient.

80 Sound & Communications www.soundandcommunications.com What’s required is a system in which the installer can make intelligent design decisions, pictured in Figure 3. Perhaps the client watches Blu-ray content only in the boardroom, but watches TV in both the boardroom and at the trading desk. With the proper switch, the installer can configure its input EDIDs independently. Now, the Blu-ray player may send the full 1080p Deep Color surround sound signal to the boardroom. The cable box, which must support both rooms, is limited to 720p. This Figure 3. isn’t much of a sacrifice, because ca- content are licensed and authorized to tication times, disabled outputs and ble companies don’t actually transmit do so. After successful authentication, complete system failure. Implementing 1080p content anyway (though some the TMDS data streams are encrypted HDCP is a complicated process, and cable boxes will upscale to 1080p). A to prevent other devices from eaves- there’s plenty of room for error. really nice switch will accept surround dropping on the content during trans- But problems can occur even on audio for the boardroom, and down- mission. well-implemented devices. During the mix it to basic stereo for the trading A single point-to-point HDCP link last step of authentication, repeaters desk. can involve only one HDCP transmit- must inform the content source of the When designing multi-room HDMI ter chip and one HDCP receiver chip. downstream connections. Every HDCP installations, be sure to select equip- If a repeater device requires access to device has a unique ID, known as a ment with intelligent EDID control. the content, it must feature an HDCP KSV, which must be passed up to the If necessary, consider switches with receiver for decryption. The repeater source. Unfortunately, all sources have audio downmixing support as an up- must then re-encrypt the data with a hard limit on the number of KSVs grade. an HDCP transmitter on each of its they’ll accept. The HDCP specification outputs. The repeater informs the allows for up to 127 devices, but sourc- HDCP Encryption upstream device of its downstream es usually support far fewer. Many sup- • HDCP: HDCP encryption is an- connections, but it is the repeater’s port fewer than 10 devices, and at least other complicating factor in HDMI responsibility to maintain those con- one popular cable box in the field only installations. The HDCP system first nections. supports one television! authenticates HDCP devices and then HDCP has caused a lot of interop- If a repeater presents a source with encrypts the content. Authentication erability issues in HDMI installations. more KSVs than it supports, the source occurs over the DDC interface and Clients have been plagued with flash- will stop transmitting content. Unfor- ensures that all devices receiving the ing and snowy screens, long authen- (continued on page 108)

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September 2008 81 down to business (Continued from 20) and set appropriate limits on the more so when several rooms are there is value and fulfillment from new talent potential. There are switch. If the client attempts to involved. Switching systems must working in this industry; other- some resources set aside for this route the content to too many de- be easily customizable to handle wise, we would be doing some- activity at both organizations, but vices, content will only drop out in HDCP and EDIDs intelligently. thing else. they require each of us to be a the excess rooms. Furthermore, Be sure to choose a vendor with In order to broaden our work- part of their use and there doesn’t the client will be presented with a proven track record managing force, the industry requires more seem to be a visible, formal pro- an informative error message. bi-directional digital communica- outreach and recruitment...more gram of development. Installers must be aware of KSV tions, and one who can offer a per- development at the local level. We In general, labor markets tend limit issues in any HDMI installa- sonal level of technical support for need to attract more people to the to right themselves based on tion that involves more than one any problems that may arise. n industry by creating awareness supply and demand, but this of- display. Be sure to research how and incentive. Both NSCA and In- ten takes years, and sometimes your equipment handles scenarios References foComm International have train- never occurs in a local economy. that violate source KSV limits. 1 “Hollywood reportedly in agreement ing and certification programs, The shortage we are experiencing Like it or not, HDMI is here to to delay forced quality downgrades for and educational foundations, but will not reverse itself quickly, but stay. There are many pitfalls in Blu-ray, HD DVD,” by Ken Fisher. Ars these initiatives focus mainly on we can help it by doing what we store for the uninformed installer, technica: http://arstechnica.com/ news.ars/post/20060521-6880.html. those of us already in the indus- can as individuals to help bright especially in larger installations. 2 “MPAA wants to stop DVRs from re- minds to consider the industry as And the problems aren’t limited try. We have to reach outside of cording some movies,” by Matthew our known circles and bring in an opportunity. n to cable-length issues. Process- Lasar. Ars technica: http://arstech- Flight of Imagination ing EDIDs and managing HDCP nica.com/news.ars/post/20080608- requires microcontrollers running mpaa-wants-to-stop-dvrs-from-record- (Continued from 77) complex state machines, even ing-some-movies.html. entertainment designers to work center or retail development. Steve on projects, the opportunity to Thorburn has made it one of his av links integrate advanced AV systems goals as TEA president to ensure (Continued from 69) into what at one time might have that developers are well aware of positioned for ease of use,” noted wins of American champions. been a more straightforward ap- the benefits themed entertainment White. “The racks look great, A 30-minute guided tour of the plication continues. providers can produce. with just the right ratio of equip- Research and Test Center reveals “Certainly, developers are Thorburn stated, “We will be ment-to-blank panels. All signal to guests the sophisticated confor- aware of all that is out there,” working hard to let everyone know cables and power cords enter at mance testing procedures of clubs claimed Edwards. “They look at that the themed entertainment in- the top and are artfully dressed. and golf balls in demonstrations of all aspects of a project, and want dustry, including architects, writ- We’ve used rule-book cable man- the COR Test, Indoor Test Range to make sure that everything not ers, designers, fabricators and AV agement right down to the Mylar and Iron Byron robotic test golfer. only achieves the project’s main specialists, is necessary to create wire tags.” Scheduled to open this month, mission, but also works to make the best immersive and interactive All rack items are labeled and The USGA Museum Putting them money in the process.” That experiences of tomorrow.” n a set of laminated system draw- Course, a 16,000-square-foot means that AV designers must be For more information about the ings and network assignments green with humps and swales, will more involved in the project to companies supplying information are clipped inside a rear door. offer passionate golfers a unique ensure that the AV components here, contact: and challenging experience as all support the main narrative in --Maris Ensing, Mad Systems, they putt with replica antique [email protected] Beyond AV the project. In addition to being clubs and balls. --Dan Jamele, MediaMation, danj@ The basic tour of the USGA Mu- knowledgeable in the technical mediamat.com seum is enhanced with rich media A visit to the new USGA Mu- specifications, AV designers, as --Steven Thorburn, Thorburn Associ- that is excellent in both produc- seum, with its powerful interac- Brian Edwards likes to say, have ates, [email protected] tion and presentation. Also part tive exhibits and unparalleled col- to “use the other side of their --John Miceli, Technomedia, jmiceli@ of the tour is the Hall of Cham- lection of memorabilia, promises brain” to embrace the creative gotechnomedia.com or Jessica John- pions where, organized by year, to renew your golfing spirit and component. son, [email protected] engraved bronze plaques trace the elevate your game. n Because, if one thing is certain, --Brian Edwards, ETI, brian. it’s that people will still want to [email protected] or Roberta how: business be entertained and told a story, Perry, [email protected] --Tim Gantz, Noah’s Ark, tim@noah- (Continued from 30) whether it is in a theme park, sarkwaterpark.com their attention, and you increase the ditional sense of purpose in life museum or even a corporate chances for youth to retain the mes- and place in the ministry. HDMI: not just cable length sages you are communicating. I believe that communication • Media use seems to be sewn technologies are effective chan- (Continued from 81) into teenagers’ DNA. Train nels for communicating with tunately, KSV limits typically rooms, typically without so much them to use technologies ap- teenagers. I also believe that un- aren’t an advertised feature. Cli- as an error message. propriately. Then allow them to derstanding the use of communi- ents won’t even realize they have Again, a solution is required that participate with the media team cation technologies in youth min- a problem until they try to route a allows installers to make intelligent during youth services and during istry will create new opportunities given source to too many repeat- design decisions. Professional services in the main auditorium for you to conduct business with ers and displays. Audio and video switches will allow the installer to (adult services). Allowing teens houses of worship. But what do drop inexplicably in all connected test the KSV limits of each source, to participate will provide an ad- you believe? n

108 Sound & Communications www.soundandcommunications.com