The electronics world is hiding a nasty secret from you: if you're not careful, you can purchase a DVI display that will become a useless paperweight in a few years. If your display isn't HDCP-compliant or if the DVI/HDCP support is buggy, you will face a lot of heartache trying to get it work with the latest peripherals. Here we tell you why, how to identify a buggy display, and how to future-proof your next display purchase.
First-generation HDTV displays used analog component video (Y Pb Pr) connections to display high-definition (i.e. 1080i or 720p) content. While component video produced a stunning improvement in picture quality over standard definition S-Video or composite video connections, it remained vulnerable to piracy and poor cable quality. Because the content isn't encrypted, any competent hacker could capture the component video signal and save a high-resolution copy for illegal redistribution purposes. Furthermore, since it's an analog connection, cheap cables could impact picture quality.
Surprisingly, both of these concerns are largely theoretical. HD content is too massive for pirates to burn onto a DVD or transport over today's broadband connections (it could take days to upload a full-length 20Mbps movie). In addition, since HDTV sets remain relatively expensive, most people aren't going to try to save a few cents on cheaper component video cables, so the cable quality issue is moot.
Regardless of the validity of these concerns, studios and consumer electronics companies were anxious for a digital alternative to component video. Fortunately for them, during this same timeframe, the computer industry was in the midst of transitioning from analog VGA connectors to the Digital Visual Interface (DVI). Since DVI can transmit up to 5Gbps of uncompressed video content (far in excess of HD transmission rates), it is an ideal solution for newer display technologies like plasma or LCD since it enables manufacturers to create an all-digital display solution.
Another benefit of DVI is its use of the Extended Display Identification Data (EDID) standard. EDID lets other devices ask the display about what resolutions and scan rates it supports and also its native, or preferred, resolution. This allows users to insert (or hot-plug) a display into any DVI device and automatically select the optimal video resolution.
HDCP: An Irresistible Force
Although DVI was designed as a computer-centric solution, display manufacturers adopted it en masse. Given its digital nature, cable quality concerns were virtually negated. In addition, EDID also reduces complexity. Before DVI/EDID, users had to know or guess if their display supported 480p, 720p, or 1080i resolutions. If they guessed wrong, the monitor could go berserk and display video noise. The resultant mess was likely to generate support calls as novice users struggled to undo the damage. By contrast, with a DVI display, the device generating the HD signal knows beforehand what resolutions the display supports so it should be considerably harder to select an invalid video-output resolution.
But the real benefits of DVI can only be seen on pure digital displays such as LCDs and some plasmas. An all-digital solution shows you video lines that typically can't be detected on a tube fed by a component connection. This occurs for two reasons. First, even on many flat-screen displays, the curve of the tube causes a few lines of video to be lost. Second, the analog-to-digital conversion required by component cables may cause small portions of the video data to be lost.
While DVI is easier to use, is less subject to cable quality issues, and produces a digital picture, it still is vulnerable to piracy. In fact, since it's a digital interface that transports uncompressed and unencrypted digital video data, it is even more frightening to movie studios than component video connections since a pirate can now make a perfect digital copy of the content. However, the High-bandwidth Digital Content Protection (or HDCP) protocol can be used to secure DVI and mollify Hollywood's security concerns with DVI [see "Changing of the Guard," www.emedialive.com/Articles/ReadArticle.aspx?ArticleID=4928].
HDCP provides a secure communication channel from the transmitter (i.e. DVD player, cable set-top box, etc.) to the receiver (or HDTV display). This secure path is established after three steps: initialization, authentication, and a periodic handshake. During initialization, the transmitter validates that the receiver is able to perform basic HDCP communication. If the display passes this test, the transmitter and the receiver exchange security information and establish an encrypted session. Once the communication channel is established, every two minutes the transmitter and receiver perform a handshake. Should the handshake fail, the whole process is restarted. This handshake prevents hackers from swapping in a bogus device after successful authentication.
As a consumer, you have no control over when HDCP is used to encrypt content between your display and cable/satellite set-top box. In fact, even the movie studios don't have explicit control over HDCP activation. The real power broker in the HDCP sweepstakes is your cable or satellite provider. The content owner may place the Redistribution Control Descriptor (aka Broadcast Flag, RCD) or DTCP descriptor into the stream, but it is the provider that controls what security protocol is enforced when these flags are detected in the stream [see "Checkered Flag," www.emedialive.com/Articles/ReadArticle.aspx?ArticleID=5098].
One reason the provider has such a powerful position is the immature state of the standards. The FCC will not require support for the broadcast flag until July 1, 2005, and even then, it only mandates that digital interfaces be secured when the RCD is present—it doesn't specify that HDCP be used on DVI interfaces. Likewise, the DTCP descriptor only requires that DTCP be used to protect the IEEE 1394 interface when the DTCP descriptor is present. It is up to the hardware vendor to secure the DVI interface when the DTCP descriptor is present. Consequently, although neither the FCC nor the DTLA (Digital Transmission Licensing Administrator) require HDCP, it is the obvious choice to secure DVI connections.
Since the broadcast flag is in its infancy, it's doubtful that many content providers will place the flag in their content in the near future. However, your cable or satellite provider can choose to enforce HDCP regardless of the state of the broadcast flag for DTCP descriptor. For example, DirecTV offers a test channel that lets you detect if your HDCP equipment is working properly. Similarly, some cable companies enforce HDCP for all content transported over DVI (both HD and SD). Unfortunately, since DVI/HDCP sets are just beginning to be deployed en masse, there is no exhaustive list of cable providers that require HDCP. You will need to call your local cable provider and ask about HDCP enforcement.
Severe Growing Pains
In an ideal world, if you try to connect a non-HDCP or hacked display to an HDCP set-top, the set-top will display an error when it tries to activate HDCP functionality. Similarly, you should never see an HDCP-compatibility warning if you connect an HDCP-compliant display to an HDCP transmitter. For the vast majority of DVI/HDCP displays, this all works as designed. Alas, several brands of displays were manufactured long before there were a significant number of transmitters to verify HDCP functionality (especially those built in 2001 and early 2002). As a result, these displays can exhibit very quirky behavior ranging from total incompatibility with all DVI/HDCP devices to occasional video glitches when tuning channels.
In general, there are three categories of display-related HDCP errors that you will encounter: raw communication problems, timing incompatibilities, and video glitches. Raw communication errors happen when the HDCP transmitter can't detect that your display is HDCP-compliant. If you have a DVI display without HDCP, it may generate a stunning picture today, but you are on a dead-end path with no potential workarounds three years down the road.
The HDCP protocol usually requires hardware acceleration for security and performance reasons, so a software upgrade normally is not possible. When your provider decides to enforce HDCP protection, your best-case scenario will be 480p or NTSC resolution video on the unprotected DVI output. Worst case, you'll get a warning advising you to use the component video connection since your DVI connection has been deactivated.
Even if you purchase an HDCP display, you still aren't immune from raw communication problems. For instance, some displays don't accept HDCP commands for several hundred milliseconds after they have been turned on. While this may seem like a trivial bug, your transmitter may erroneously determine that the display isn't HDCP compatible and display a HDCP warning message every time you turn on the display. Although there are ways to work around this problem (i.e. turn on the transmitter after the display has warmed up or hot-plug the DVI cable into the transmitter), these workarounds can be cumbersome especially compared to analog displays that aren't susceptible to such problems.
Timing is Everything
At least you know you definitely have a problem with a solution when raw communication errors occur (they require either a software or hardware upgrade or some cumbersome workaround procedure). By contrast, timing problems between the HDCP transmitter and receiver appear to be random and don't have easy fixes. For example, most of the time your transmitter may refuse to communicate with the display regardless of what workarounds you attempt. Then suddenly, your DVD player or set-top is able to establish an HDCP session with the display and you see perfect video.
Even after an HDCP session is established, you still may be besieged by basic communication problems. For instance, if your receiver and display are unable to consistently perform the HDCP handshake, you may see HDCP warnings flash onto the screen. If the handshake issues between the display and the transmitter are severe, the video could be cut off completely. While this category of problem is exceedingly rare, it can be frustrating if it happens on your monitor.
The final timing issue revolves around channel surfing. Each time you change channels, the entire HDCP authentication process must be re-initiated. Theoretically, this activity should be undetectable. Unfortunately, some displays have older HDCP chipsets that require a complete reset (or re-initialization) before an HDCP session can be re-authenticated. This reset may cause your screen to go blank for a short period, or it can cause a blast of video noise.
Although most HDCP bugs and artifacts tend to be display related, terminals also may have channel-surfing bugs. Since the video stream must be re-authenticated each channel change, poorly optimized terminal set-top box software will cause significant degradation in channel change time (in worst-case scenarios, the HDCP cycle may add an additional second to the channel change process).
How Can I Avoid These Heartaches?
After seeing the plethora of problems you can encounter with an HDCP display, you're probably pretty anxious to test your existing or future display for compatibility issues. If you live in an area served by by DirecTV or a cable company that requires HDCP, it's relatively easy to determine if the display you're interested in is fully HDCP compatible.
For cable set-tops that require HDCP, you just connect your DVI display to the set-top box. If you see video, then you know basic HDCP authentication is working. DirecTV subscribers should tune to channel 201 (Customer Server). If your DVI equipment is functional, then you'll see video. Otherwise, you'll be greeted with an HDCP warning.
If you subscribe to a different cable or satellite provider, then it may be a challenge to concoct a HDCP compatibility test scenario. One alternative means of testing HDCP compatibility is to connect an HDCP-enabled DVD player to your display. Please note however, that your cable/satellite transmitter provides a more robust HDCP-compatibility test as there is no easy way to simulate channel change problems with a DVD player.
After you've verified that the display supports basic HDCP communication, you should proceed to more vigorous compatibility tests. These tests include turning the display on and off while viewing content, changing channels rapidly, and, finally, leaving the transmitter on a single channel for twenty to thirty minutes. If the display is able to pass these tests, then you can feel relatively confident that the display's HDCP functionality is robust and therefore it is safe to purchase.
A second means for validating HDCP compliance is checking home theater sites on the Web. Probably the most comprehensive site to track HDCP-compatibility problems is the AV Science Forum (www.avsforum.com). Members on this forum don't just gripe about compatibility woes, but also compile lists of compliant and problematic HDCP displays and post notices when firmware updates become available.
A Moving Target?
Unfortunately, even if you find a display with solid HDCP firmware within the next 12-24 months, you may possibly encounter compatibility issues with newer set-top boxes equipped with High-Definition Multimedia Interface (HDMI). Given the DVI/HDCP compatibility issues that the industry is actively resolving, you may wonder what's spurring the switch from DVI to HDMI. DVI is a general-purpose video interface that was adopted "as-is " from the computer industry. By contrast, HDMI has been tailored for the consumer market and contains consumer-friendly features such as smaller, easier-to-plug-in connectors, universal remote control capabilities, and the ability to transport both audio and video in a single cable (this reduces cable clutter). Since these benefits far outweigh the few compatibility issues that might arise, the HDMI transition is inevitable.
To accommodate the new feature set of HDMI, a new revision of the HDCP protocol (HDCP 1.1) has been published. The designers of HDMI and HDCP 1.1 took great pains to ensure backwards compatibility with DVI/HDCP (i.e. you can plug the smaller HDMI cable into a DVI connector and still see video). Therefore, theoretically, you should be able to connect an HDMI and HDCP 1.1 transmitter to your existing DVI/HDCP 1.0 display without incident.
Alas, given that there are compatibility issues between pure HDCP 1.0 devices, it is logical to assume that there will be some compatibility issues between HDCP 1.1 and HDCP 1.0 devices. Since there's no way to anticipate future compatibility issues, it would be advisable to ensure that all HDCP-enabled devices you purchase are software upgradeable. That way, if you encounter a bug, you can download a firmware update rather than tossing your expensive display into the garbage.
Conclusion
While the transition from analog component video cable to DVI produces sharper images on digital displays, the imposition of HDCP to secure the DVI connection has introduced bugs in some displays that can frustrate consumers. You can avoid many of these aggravations by performing some preliminary HDCP tests before you purchase your DVI-enabled display. However, regardless of what HDCP product you buy, it needs to be software upgradeable. This will ensure that the device doesn't become a paperweight when you encounter HDCP-related bugs.