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1 HDTV Home Theatre Equipment DVD/D-VHS Reviews The Essential Home Theatre Resource WIDESCREEN REVIEW DVI And HDMI Interfaces For A New Age AGE HD-DVD Hollywood s Wish List DTS: : A A Ten-Year 40 DVD REVIEWS History Home Theatre WSR Review ReviewTM Products In SIM2 HT300 Plus Samsung SIR-T165 HD Set-Top Tuner $5.99 US $7.99 Canada Volume12, Number 2, Issue69 February

2 DVI And HDMI Digital A/V Interfaces For A New Age A L E N K O E B E L A New Age Of Home Video The signs are obvious: We are entering a new age of home video. Call it the Age of High Definition. Accessibility to digital HD content is accelerating, both via broadcast and for the first time, with the advent of D- Theater D-VHS, on pre-recorded media. Proposals too many of them! for a highdefinition version of DVD are being pitched in earnest by consumer electronics manufacturers. User-friendly display technologies for viewing HD content, such as plasma and DLP, are finally maturing and becoming affordable to millions of people. And battle lines are being drawn in what may prove to be the legal fight of this or any decade: the issue of copyright protection for digitally transmitted works. A common thread through all of this is the humble audio/video interconnect. At the dawn of this new age, the way we connect audio and video components together has become more important than ever. Almost universally, the entertainment industry has decided that digital A/V interfaces are the way of the future. One reason is that they provide the potential for superior presentation of content compared to the so-called legacy analog interfaces common now. More significantly, they provide unprecedented protection of content from unauthorized copying. Two suitable digital A/V interfaces have come to the forefront: IEEE 1394 (also known as FireWire and ilink ) and Digital Visual Interface (DVI). In this article, I examine DVI and its recent descendant, High Definition Multimedia Interface (HDMI ). I describe the technology and capabilities of DVI-based interfaces, their practical limitations and how they ve been implemented in current products. Last, but not least, I discuss the political issues and how they might affect our home video future. Digital Visual Interface (DVI) Even as recently as one year ago, there were relatively few consumer products with DVI interfaces. Today, there are many. DVI started life in 1999, a creation of the Digital Display Working Group led by Compaq, Fujitsu, Hewlett-Packard, IBM, Intel, NEC, and Silicon Image. (The basic technology of DVI has actually been in use even longer in a slightly older interface known as DFP, which except for the type of connector is largely compatible with DVI in its simplest form.) DVI was originally intended for connecting PCs with flat-panel LCD monitors and that is still its most common application. If you ve bought a mid- to high-end PC lately, chances are good it includes a DVI output for this very purpose. DVI is fundamentally a 24-bit digital RGB interface based on a signal technology called Transition Minimized Differential Signaling (TMDS). A single DVI link consists of three pairs of differential, low-voltage digital signals one each for the red, green and blue components, and including synchronization (sync) information plus a fourth pair for transmitting a pixel clock. The data for each 8-bit RGB component is transmitted as a serial bit-stream with a maximum bit rate of 1.65 Gigabits per second (Gbps). The maximum data transfer rate for a single DVI link is thus 4.95 Gbps. That is fast by anyone s standards! Each 8-bit byte is actually sent using 10 bits part of the method used to minimize transitions so the actual, usable bandwidth for pixel data is 3.96 Gbps, which is still a very high number. This much bandwidth enables a single DVI link to handle all of the HDTV formats defined by the ATSC in uncompressed form without breaking a sweat, as well as computer formats as high as 1600 x 1200 (UXGA) at 60 Hz. Even the pinnacle of high-definition formats, 1080p/60 (1920 x 1080 at 60 Hz progressive), is well within its grasp. The DVI standard actually allows up to two links on the same connector, using extra pins reserved for this purpose. This requires only three additional signal pairs, since the two links share the same clock. Dual-link DVI has a maximum data rate of 9.9 Gbps (a usable pixel throughput of 7.92 Gbps), which will handle pixel formats as high as 2048 x 1536 (QXGA) at 60 Hz. The second link could also be used, in theory, to allow more than 24 bits per pixel but to my knowledge there are no products that use it in this way. At present, very few products use dual-link DVI. In addition to digital video and clock signals, DVI includes a low-speed, bi-directional communication link, based on Philips I2C serial bus, to allow the PC or video source to talk to the display. This link is known as the Display Data Channel (DDC), a standard for communication between PCs and monitors established by the Video Electronic Standards Association (VESA). The source uses the DDC link to read data about the display s properties from a non-volatile memory. This allows a PC display card, for example, to learn about the pixel format of an LCD monitor and set its output to match. The communication protocol follows the VESA Enhanced Extended Display Identification Data (E-EDID) standard. The DVI standard actually allows the transmission of analog RGB and sync signals as well as digital video signals. When this option is used, usually to eliminate the separate connector that would otherwise be required, the DVI connector includes a ground blade with 4 pins surrounding it in addition to the normal 24 pins (see Figure 2 WIDESCREEN REVIEW ISSUE 69 Page 1/6

3 1). Connectors with these extra pins are called DVI-I while those without are called DVI-D. (DVI can also be used to transmit only analog signals, but this is not common.) In the balance of this article, the analog option is ignored and the digital-only connection is called simply DVI. High-bandwidth Digital Content Protection (HDCP) In response to the expressed desire of content providers, specifically the Hollywood studios, to protect their home video products Intel, with assistance from Silicon Image, developed the High-bandwidth Digital Content Protection (HDCP) standard. The specific intent of HDCP is to prevent content transmitted by DVI from being copied. HDCP has been endorsed by most of the major Hollywood studios as well as by the satellite and cable industries. By design, a DVI connection is point-topoint between a single transmitter (most often a video source) and a single receiver (most often a display device). Briefly stated, HDCP performs its content-protection function between these two devices using the following processes. The first is called Authentication and Key Exchange (AKE). In this process, the transmitter verifies that the receiver is licensed or authorized to receive protected content. This is done using a set of secret and protected digital signatures or keys that are stored in both the receiver and the transmitter. Exchange of key information occurs over the DDC communication link. Once the receiver has been authenticated, data transfer is allowed. To prevent eavesdropping by another device (or, more correctly, to make such eavesdropping useless) the data flowing across the interface is encrypted by the transmitter and can only be decrypted by an authenticated receiver. Each pixel of video data is separately encrypted. (This has no affect, by the way, on the data transfer rate.) Viewed on an unauthorized display device, encrypted video will look like random noise. At least, it will look that way for a few seconds. As an additional protection measure, the transmitter re-verifies the receiver s authentication about every two seconds (specifically, within 128 fields of video). If it doesn t receive verification, it stops transmitting entirely. The system will re-attempt AKE if the DVI connection is broken then re-established (say, by hot-plugging the connector). As a final protection measure, HDCP allows a receiver s authorization to be revoked. This would be used, for example, to shut down hacked or rogue equipment. The key values associated with compromised devices are kept in a key revocation list, carried by System Renewability Messages (SRMs). Updated lists would be included in pre-recorded or broadcast content, or would be received from another upstream device. DVI-HDTV When HDCP is added to DVI, the result is often called DVI+HDCP. When this is used on an HDTV, HD monitor or a set-top box, a further standard is usually applied: IEA/CEA-861 (currently 861-B). This defines how to send DTV signals standard, enhanced and high-definition over uncompressed digital interfaces such as DVI, and includes such details as video signal timing, pixel formats, and the exact structure of data transfers. When this combination is used on high-definition-capable products, the interface is commonly known as DVI-HDTV. HDMI: New Kid On The Block By design a DVI connection, with or without HDCP, carries only RGB video (and sync) information on its high-speed TMDS links. It should do a lot more than this if it s going to be particularly useful as an interconnect between consumer A/V components. This was the motivation behind the creation of the High Definition Multimedia Interface (HDMI), the result of a collaborative effort between Hitachi, Intel, Matsushita (Panasonic), Philips, Sony, Thomson (RCA), Toshiba, and Silicon Image. HDMI is brand new V1.0 of the specification should be released by the time you read this. A number of Hollywood studios, satellite TV providers and consumer-electronics manufacturers have already expressed their support for the standard. Products that incorporate it aren t expected to appear in any significant numbers until late 2003 at best. Based in essence on DVI-HDTV, HDMI adds the ability to carry digital audio and to distribute basic control data between A/V components. To make it even more attractive as a consumer interface, it uses a Figure 1 smaller connector and adds enhanced support for high-definition digital component (YCbCr) formats, going beyond those defined in IEA/CEA-861-B. HDMI s audio handling is designed to be future-proof and backward compatible. It can not only carry the compressed multichannel, digital-audio formats we all know and love, such as Dolby Digital and DTS Digital Surround but can also carry uncompressed digital audio up to eight channels worth, supporting a variety of sample sizes and rates up to 24 bits and 192 khz (all of these maximum specifications can be achieved simultaneously when transporting HD video formats). HDMI transports its audio data during blanking intervals, a scheme that does not affect the available video bandwidth. And it is completely backward compatible with earlier DVI implementations, older devices simply ignoring the audio data. HDMI adds control data in a different way. Rather than multiplex information onto a TMDS channel, or by using DVI s existing DDC link, HDMI adds a new communication signal. This acts as a bi-directional bus that is connected in common to all HDMI devices in a chain. Known as the Consumer Electronics Control (CEC), the communication protocol is based on AV.Link, a popular standard used in European A/V products. CEC is meant to solve many of the simple problems commonly experienced by consumers trying to get disparate pieces of equipment to work together. For example, it makes it easier to use a single remote to control multiple devices, eliminating the need for infrared repeaters. And it allows a sequence of different instructions to be sent to multiple devices in response to a single user command (such as play a DVD ). With any luck, it might even help to banish the dreaded, flashing 12:00. As with DVI-HDTV, and unlike basic DVI, HDMI explicitly supports component (YCbCr) video formats, including the commonly used DTV formats (480p/60, 720p/60, and 1080i/60) and their 50 Hz (European) counterparts. Because it fully supports IEA/CEA- 861-B, it also allows 1080p signals at 24, 25, 30, 50, and 60 Hz. Support for 1080p/24 Page 2/5 WIDESCREEN REVIEW ISSUE 69 3

4 could make it possible for progressive movie frames to be directly output from a 1080-line HD source without requiring 3-2 pulldown. Although a CRT is not able to directly display such a signal because of objectionable flicker, a DLP display might if properly designed. Today s DLP Cinema projectors do exactly that. HDMI, like DVI, actually supports almost any display format that fits within its maximum data transfer rate. And, again like DVI, HDMI optionally supports a dual-link connection. However, in my opinion, dual-link is likely to be just as rarely used as it is with DVI. It s not really needed. HDMI over a single link already beats the professional SMPTE 292M serial HD interface, which cannot handle 1080p/60, hands down (except for usable cable length more on that below). HDMI provides other features intended to ensure high image and sound quality. A source can specify image parameters such as color space (standard- or high-definition) and aspect ratio, as well as audio parameters such as coding method (for compressed audio), sample rate and channel allocation. Of particular note is that while IEA/CEA-861- B supports only 8 bits per RGB or YCbCr component (24-bit 4:4:4 for either or 16-bit 4:2:2 for YCbCr), HDMI also allows up to 12 bits per component for 4:2:2 YCbCr signals, even for 1080p/60. In comparison, professional HD mastering and D-Cinema currently use only 10 bits per 4:2:2 component, which allows roughly four times as many gray levels as 8-bit for smoother tonal reproduction (especially noticeable in darker tones). It remains to be seen how many HDMI products will support and make effective use of display formats with more than 8 bits per component, but I m cautiously optimistic that 10-bit products will become fairly common, at least at the high end. Finally, HDMI uses a brand new 19-pin connector that is considerably smaller than the DVI connector (see Figure 2). This will be particularly welcome on portable projectors and other small A/V components where panel space is at a premium. The smaller connector should also be much easier to fish through conduits and walls for permanent home theatre installations. Implementation And Compatibility Issues As mentioned above, many consumer A/V products introduced over the last year or so now include a DVI interface. Some products, usually older ones or those originally designed for commercial use, implement plain, first-generation DVI. Later products add HDCP (DVI+HDCP), or HDCP and compliance with some form of IEA/CEA-861 (DVI-HDTV). Unfortunately, since the connector can look the same in each case (its appearance differing only on whether analog RGB inputs are included) it s not always easy to tell what product uses which variant. You ll have to hope the product s data sheet properly specifies. Choosing a display whose DVI port does not support HDCP means, of course, that it will not be able to show protected content. Choosing a display that includes HDCP but lacks support for IEA/CEA-861 is not necessarily as much of a problem. All DVI sources must be able to output 24-bit RGB, which DVI-equipped displays must be able to accept, and must be able to query a display to discover what image formats it supports. Through this mechanism some compatible format can usually be found, although it may not be the display s optimum mode. Unfortunately, even when source and display use identical variants of DVI there can be problems. Because of a multitude of factors, including differences in transmitter and receiver chip designs, board layouts, and the quality of the interconnecting cable assembly, achieving an artifact-free image can be a hit-or-miss affair. Cable length in particular can be a serious issue. The DVI standard doesn t actually specify a maximum cable length; what works in practice for a given setup will depend on the pixel clock rate of the video format in use combined with all the other factors listed above. You might achieve perfect results using as much as 20 meters of cable, or you might start seeing artifacts with as little as 2 meters! Unfortunately, as with most digital signals, DVI does not fail gracefully. In the case of RGB data, artifacts typically consist of intermittent bright red, green or blue pixels, depending on which channel an error appears. The more errors, the higher the number and frequency of these sparkles. Companies such as Extron ( and Gefen ( sell various kinds of boxes that can extend DVI signals up to 100 meters. Other companies offer cables that actually use fiber optics; the electronics for converting to and from DVI are integrated into the plug housings and draw power from the DVI ports. For consumer use in particular, it is important that the extender applies its magic to the DDC signals as well as to the TMDS channels, since HDCP depends on DDC for proper operation. Extenders like those described above can only be considered work-arounds since they tend to be too expensive for the vast majority of potential users of DVI. Fortunately, a bona-fide solution to the cable Figure 2 length problem is near at hand. Adaptive cable-equalizer chips designed to be put in front of DVI receivers are coming from several semiconductor manufacturers (some may already have been introduced by the time you read this). Depending on clock rate and cable quality, these can extend DVI anywhere from 30 to 50 meters, which is more than enough distance for most home theatre installations. These chips should substantially reduce the cost of extender boxes and cables. Or, better yet, they could be designed directly into A/V products. Still, until the industry gains more experience with DVI, it won t be all clear sailing. As Steven Hill, President of specialty-cable manufacturer Straight Wire ( wire.com), says DVI is a major step forward but users should be cautious. You can t just plug any DVI cable into any component and expect it to work well. Will HDMI share DVI s present limitations and compatibility problems? Because there aren t any products yet that use it (at time of writing), there s no way to know for sure. But it s not unreasonable to expect that by the time they do appear, the extra experience with DVI gained by consumer electronics manufacturers, coupled with the availability of better chips and better compliance testing, will lead to calmer seas. Except for the issues discussed above, connecting between HDMI and earlier DVIbased devices should be relatively painless. Simple, passive adapters for going both ways will almost certainly be available. Such adapters will not pass HDMI s special CEC communication line. And since DVI is only for video (with sync), any audio data present on an HDMI output will be ignored by a downstream DVI device. Naturally, if a downstream device s DVI input lacks HDCP, it won t be able to show (if it is a display) or pass through (if it is a DVI switcher or repeater) protected content from the HDMI source. 4 WIDESCREEN REVIEW ISSUE 69 Page 3/5

5 Why Digital? The Politics Of Content Protection The YPbPr analog HD interface we use now (technically known as EIA/CEA B) is capable of excellent image quality (as is the equivalent analog RGB interface). So why go digital? The standard answer, and a valid one, is that it can lead to even higher image quality, or at least make the same quality easier and less expensive to achieve. We ve already seen audio-only interfaces go through a digital transition with those same benefits. (Ironically, because of copyright issues the highest resolution digital-audio signals from DVD-Audio and SACD are still analog-only.) Not only does a digital interface for video avoid multiple, unnecessary conversions between digital and analog signals, it can also carry more information about the source content to the display, making an optimum image easier to achieve. And a digital interface can carry video, audio, and control information all on one cable, which should go far toward eliminating the usual rat s nest of cables we currently suffer (see Figure 3). But many people suspect that better quality is merely the bait that hides what could prove to be a very sharp hook: content protection. The Hollywood studios, represented by the Motion Picture Association of America (MPAA), want secure digital connections primarily to plug what they call the analog hole. As Richard Parsons, CEO of AOL Time Warner put it, Once content is in the clear in analog form, it can be converted back into a digital format, which can then be subject to widespread unauthorized copying and redistribution, including over the Internet. What Parsons warns about has already happened with standard-definition content from DTV broadcasts and DVD (although in the latter case directly from the digital data on the DVD because its protection system, CSS, was cracked). So the Hollywood studios fear that the same thing could happen with HD content (which is far more valuable to them) is understandable. But how likely is it? It is true that, even today, it is possible to buy off-the-shelf equipment that allows analog HD signals to be converted to digital and recorded onto professional HD tape formats. I won t name any equipment, but I will say reasonable quality can be achieved for an investment as low as $30,000US (roughly double that for the best possible recording quality). Clearly, this isn t the sort of thing the average consumer is likely to try. But it is easily within the reach of professional pirates, who could use the resulting mas- ter tapes to create and replicate D-VHS copies or, someday, HD-DVDs. Two different methods have been proposed to defeat pirates seeking to exploit the so-called analog hole. One method is to eliminate analog interfaces entirely from future digital A/V products. Another method would employ a watermark embedded in the analog signals that would be detected by analog inputs on new displays and digital devices (only), whose A/D converters would be mandated to include watermark detection capability. To date, little progress has been made on a workable watermark detection scheme. Proponents of the first method, however, are charging full steam ahead: Draft legislation introduced last year by Representative Billy Tauzin (R-Louisiana) would require the elimination of all analog outputs on digital devices sold after July 1, Unfortunately, this would essentially render obsolete all HDTVs, HD monitors, and HD-capable projectors without protected digital inputs. The number of such displays today is well over three million and growing. Since displays tend to be the most expensive part of any A/V system and hence are replaced the least often, it is essential that they remain compatible with newer HD source components such as tuners, satellite receivers, HD-VCRs, future HD-DVD players, and HDcapable PVRs purchased within the display s natural life. As painful as it would be for consumers, would the scenario described above really stop professional pirates? Probably not. A cryptographic analysis by a team consisting primarily of university researchers has determined that HDCP possesses a fundamental flaw that makes it relatively easy to defeat by a determined pirate. These researchers also believe that the Digital Transmission Figure 3 Content Protection (DTCP) standard used on the IEEE 1394 interface for consumer A/V devices may be susceptible to similar attacks (more about DTCP below). While copying of HD content by professional pirates may be difficult if not impossible to stop with or without analog outputs copying by consumers could likely be effectively controlled simply by prohibiting analog inputs on consumer HD recorders (and also by prohibiting such inputs on devices designed to convert them to unprotected, recordable consumer-level digital outputs), an idea espoused many times in Widescreen Review. Combined with existing digital content protection, this might well prove a sufficient deterrent to so-called casual copying without resorting to any measures that would disadvantage millions of owners of analog-input-only HD displays. Is 1394 The Answer? HDMI is not the only digital interface designed for use on consumer A/V devices. There is also IEEE The 1394 Trade Association believes, not surprisingly, that 1394 is a better choice for connecting A/V components than DVI. This opinion is fully expressed in the article IEEE 1394 vs. DVI: A Comparative Perspective by Bob Perry, Vice President of Marketing for Mitsubishi Digital Electronics America, which appeared in Issue 62, July The article can also be found at and on the 1394 Trade Association s Web site ( Mitsubishi is a member of the 1394 Trade Association. Today, 1394 has a maximum data transfer rate of 400 Megabits per second. This is not high enough to transport progressive-scan and high-definition DTV formats without compression. This key point means that Page 4/5 WIDESCREEN REVIEW ISSUE 69 5

6 within a consumer A/V system IEEE 1394 will typically always carry such formats in MPEG-2 compressed form. It also means that a display that inputs high-definition content by way of a IEEE 1394 connector must incorporate a suitable MPEG-2 decoder. All displays with integrated HD tuners which by current definition are called HDTVs do contain MPEG-2 decoders. But most do not have IEEE 1394 inputs, or allow them to be retrofitted as options (notable exceptions being models from Mitsubishi and Sony). The vast majority of HD monitors, which do not contain HD tuners (by definition), have neither MPEG-2 decoders nor 1394 inputs. HD-capable displays that lack IEEE 1394 do, however, always have analog YPbPr inputs (or equivalent-function RGB inputs). Some increasingly also have DVI inputs (either DVI+HDCP or DVI-HDTV). What this means in a practical sense is that a source device (e.g., a set-top box) that provides a IEEE 1394 output will also need to provide a set of analog HD outputs or a DVI with HDCP output (which may be HDMI in future products) or both. At least, it will if the manufacturer expects to sell many of them! Analog outputs are, at present, permitted on devices with DVI or IEEE 1394 outputs. That may change in the future due to legislation, as previously discussed. Neither the HDCP license agreement nor the DTCP license agreement, which applies to IEEE 1394, prohibit analog HD outputs. The DTCP agreement, however, does add one condition to their use: when so directed, the analog HD output signals must be reduced in resolution to no more than 960 x 540. This is known as a constrained image. When will a source device be directed to constrain the analog HD outputs? That s what current discussions in Congress are attempting to decide. The important point here is that devices with IEEE 1394 outputs protected by DTCP must allow it to happen. In contrast, the HDCP license agreement has no such requirement. Nor does it require the analog outputs to be turned off when protected digital content is being output. The source device may do either of those things, but neither is required by the license. So, given the constrained image requirement of DTCP, and depending on the desire of content producers and the whims of government, a source device with a IEEE 1394 output may actually produce worse analog output than a competing device that uses DVI (or HDMI) instead. To me, that s not a good answer to the analog problem. Perhaps in a perfect world perfect as envisioned by companies like Mitsubishi, at any rate all consumer A/V devices would connect to others using only IEEE But we don t live in that world and we probably never will. In the real world, there is a need for multiple kinds of inputs and outputs, both digital and analog. Unlike the immortals of Highlander, there can be more than one. DVI/HDMI, IEEE 1394, and even analog (at least for a number of years more) can and should co-exist, each doing what it does best. The End? Is HDMI the final digital A/V interface we re likely to see or are there yet others on the horizon ready to confuse us once again? My crystal ball is a bit cloudy, but my sense is that HDMI is indeed the last we ll see certainly the last we ll need for quite some time. Produced By This review Copyright 2003 Widescreen Review has been reproduced in its entirety from Issue 70, March 2003 of Widescreen Review The Essential Home Theatre Resource. Take advantage of our no-risk subscription offer: 13 For $34* 1 free trial + 12 monthly issues + 1 special edition + full access pass to WSR s paid subscriber Web site a 56% savings off the monthly newsstand price (over $43 savings off the cover price)! Phone WSR s Customer Relations Department at or 888 WSR SUBS, or fax at to order, or request on-line at: Or you can mail your request to: Widescreen Review, Commerce Center Drive, Temecula, CA All major credit cards are accepted. * Foreign subscription rates are $40.00US Canada/Mexico, and $75.00US International. Canada/Mexico and International Special Edition Offer Plus Shipping Cost. 6 WIDESCREEN REVIEW ISSUE 69 Page 5/5