CAPITAL CURRENTS: Must-carry technical fallout

Thu, 01/31/2008 - 7:05pm
Jeffrey Krauss, President of Telecommunications and Technology Policy

Jeffrey Krauss

The broadcaster claim
was bogus from the start

By agreeing to dual carry broadcast signals for three years after the end of analog broadcasting, the cable industry dodged the bullet called “material degradation.” Or maybe the industry won on the degradation issue because it was a purely technical issue. In contrast, FCC Chairman Kevin Martin has been beating up the industry on political issues.

The law, written in the days of analog broadcasting, says that cable operators have to carry broadcast stations without “material degradation.” That has always been interpreted to refer to picture quality. Picture quality has traditionally been measured subjectively, using panels of viewers, as specified in ITU-R Recommendation BT.500. The broadcasters argued, however, that measuring signal degradation by subjectively testing is not appropriate in the digital era, because (they claimed) the technology now exists to employ objective measurement tests.

Indeed, there has been research underway at the ITU to assess the performance of objective video quality measurement algorithms. The goal of the ITU Video Quality Experts Group was to determine whether objective picture quality standards could replace subjective testing. The conclusion, published in ITU-T Recommendation J.144, was that it could not.

But the broadcaster claim was bogus from the start. Their “objective test” was not one of those algorithms tested by the ITU, it was whether or not the cable operator carried “all content bits” of the broadcast program.

Applying that test to the broadcast signals delivered by DirecTV and EchoStar would have shut down their delivery of “local into local” broadcast signals, because the satellite operators don’t deliver “all content bits.” Rather, they take a broadcaster’s off-air digital signal, which is coded using MPEG-2 video coding, and they re-encode it using the more efficient AVC (H.264 or MPEG-4) picture coding. So the resulting bitstream they deliver to homes is maybe half the bit rate that was initially broadcast, and none of the original content bits are actually retained during the re-encoding process.

The FCC expressly rejected the broadcaster proposal, saying, “the all content bits approach is likely to stifle innovation and the very efficiency that digital technology offers, and may be more exacting a standard than necessary to ensure that a given signal will be carried without material degradation.” The FCC also said, “We particularly recognize the value of compression technologies that take the broadcast signal back to uncompressed baseband and then re-encode it in a more efficient manner without materially degrading the picture. Such advanced compression utilizes a minimum bit rate that does not reduce the quality of the resolution.”

What about the downconversion of digital broadcast signals to analog format that the cable industry agreed to deliver for three years, for viewers with analog TV sets? Cable operators have several ways to accomplish this downconversion. They could do it at the headend. They would then have to dedicate a 6 MHz channel to each of these analog channels, as they do today. Or they could do it in the subscriber’s set-top box, either by delivering an HD TV program to a set-top box and letting the box downconvert to SD, or by delivering a separate SD digital program to the set-top box in addition to the HD program.

One of the remaining technical issues, in a Further Notice the FCC released, has to do with the aspect ratio of this downconverted signal. If the digital broadcast is a 16:9 picture, but the analog TV set has a 4:3 aspect ratio, who gets to decide whether the 16:9 picture is letter-boxed or center-cut (pan-and-scanned) – the broadcaster, the cable operator or the viewer? If the downconversion to SD is done at the headend, the broadcasters want to control the signal. I believe that most cable operators would be happy if the broadcaster delivered to them a special SD or analog feed for this purpose. The broadcasters argue that the viewer should decide on the aspect ratio if the digital signal is delivered to the set-top box and downconverted there. HD set-top boxes today give the viewer that capability. But they are typically supplied only to subscribers with HD displays. Digital SD set-top boxes today can only decode SD programs, not HD programs. And viewers with SD boxes do not have any option to change the aspect ratio. So cable operators are faced with the decision about how to carry an analog broadcast signal over the next few years. They can continue to devote (or waste) a 6 MHz channel and deliver an analog broadcast signal. Subscribers without set-top boxes today could continue to watch without set-top boxes.

Or, they could deliver each broadcast signal on a single digital HD feed to everyone, and supply expensive HD boxes to subscribers with analog TVs.

Or, they could dual carry a digital HD feed and a digital SD feed (which takes up much less than a full 6 MHz channel), and supply SD set-top boxes to every subscriber with analog TV sets.

Cable operators have not yet said how they want to deal with this, and I’m not making any predictions.


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