Is HDTV doomed from the beginning?

Thu, 07/31/1997 - 8:00pm
Jeffrey Krauss, Interfacing With the Digital World and President of Tele-communications and Technology Policy
By Jeffrey Krauss, interfacing with the digital world and President of Tele-communications and Technology Policy

A year ago, I reported on a disagreement between two groups of TV manufacturers over which command language to use with this interface. Unfortunately, the disagreement still exists. There is no agreement on a standard. And time is running out.

The EIA established a standards committee, called R4.1, to develop a standard interface for a communications bus to interconnect a cluster of digital TVs, VCRs, camcorders, cable boxes and other devices in the home. Because of the high data rates involved (up to 38 Mbps on a 256 QAM cable channel), the group chose the EIA 1394 standard for the physical layer. This is also known in the computer industry as "FireWire."

The next step was to agree on a command language so that the various boxes could talk to one another. A command language is needed so that the devices in the cluster can share resources. For example, the digital VCR doesn't need MPEG decompression circuitry if the digital TV receiver has it. And the digital cable box doesn't need a tuner if the cable-ready TV has one.

The controversy

A year ago, it appeared that there were two candidates to be chosen as a command language, CAL and AV/C. CAL is the command language that was developed for CEBus, a consumer electronics network for audio/video and home automation. Thomson Consumer Electronics and Intel appear to be the main supporters of CAL.

AV/C is a command language that supports digital camcorders, TVs and VCRs. Its supporters include Sony, Philips and Mitsubishi.

Both groups claim they will have products on the market in early 1998 using their command language.

Of particular importance to the cable TV industry, CAL contains a group of commands specifically for cable boxes. AV/C is far more limited in scope. The relevant CAL commands could probably be ported or replicated in AV/C, but nobody has started that effort.

To further confuse the issue, a home automation company, Echelon, has suggested Java, a programming language used for Internet browsers and likely to be used for on-screen displays, as the command language instead of CAL or AV/C. (Java was originally written at Sun Microsystems for cable set-top boxes, according to a Fortune magazine article by Stewart Alsop.) Echelon had previously voiced objections to the use of CAL in TVs and cable boxes because it competes with a home automation network approach that Echelon uses.

The urgency

Home Box Office has announced that it will begin broadcasting HDTV movies in the summer of 1998. How will they be displayed? Here's a scenario.

HBO today delivers MPEG-compressed standard definition digital programming to cable headends. Most cable systems today decompress and convert them to analog and scramble them for delivery to the home. But so far, a few hundred thousand digital cable boxes have been delivered, and so some subscribers are receiving digital video down the cable. Because the programming is standard definition, not HD, it is decrypted and converted to analog in the cable box and displayed on an analog TV set. The digital baseband interface isn't needed.

The first digital HDTV receivers and VCRs will become available in 1998, at about the same time the first digital TV broadcasts start. The lack of agreement on a baseband interface won't be a calamity for viewers of broadcast signals, so long as consumers are careful to purchase an RCA (Thomson) digital VCR to connect an RCA digital TV, or a Sony VCR with a Sony TV.

But what about watching HBO's digital HDTV programming on the RCA or Sony TV? The signal has to go through a digital cable box to be decrypted. HBO's contracts with Hollywood won't allow them to deliver movies "in the clear" (unencrypted). So a cable-ready digital TV that has a QAM demodulator as well as a VSB demod might be able to demodulate the HBO digital signal, but it won't be able to decrypt it. A cable box is needed for that.

The digital cable boxes that are being shipped today do have a digital output port for delivering a decrypted signal to a digital TV. But the signal coming out of that port is simply a one-way digital bitstream on one pair of conductors, not the two-way FireWire network signal format, nor the FireWire physical connector. Presumably, cable box manufacturers waited as long as they could, but they had to start delivering boxes and couldn't wait any longer for the consumer electronics industry to reach agreement.

If and when the consumer electronics industry reaches agreement on an interface, I expect that it will also be incorporated into cable boxes. Meanwhile, how will we be able to watch HBO high definition movies? I don't know.

Maybe someone will build a special convertor box that converts the format of the digital bitstream coming out of the cable box to the FireWire format. I guess there will be two flavors of this box, one that speaks CAL and one that speaks AV/C. Or maybe someone will build a digital modulator box that takes the digital bitstream and modulates it to look like an 8 VSB broadcast signal on channel 3. Yuck!

My guess is that about a year from now, there will be a lot of finger-pointing, as everyone tries to blame everyone else. It won't be a good start for HDTV.


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