HD Options

[Gregg Lengling]

Will the real HD please stand up? While HD (high definition) content is blossoming on cable networks, it appears there is some double vision among programmers when it comes to what format to choose. The debate has created two strident camps–one rallying around the higher line resolution 1080i format, and the other around the more nimble, scene-changing capabilities of 720p.

In contrast, cable operators are taking a neutral stance, allowing both formats to ride their cable pipes. But that could create consequences in the future, when it comes to tighter bandwidth management and new services such as digital ad insertion.

Minding your 'p's and 'i's
While HD format is a fuzzy concept for most consumers, Federal Communications Commission guidelines do at least guarantee that they get a clear HD signal no matter what TV set they buy. FCC digital TV standards adopted in 1996 require that all digital TV sets be capable of receiving the 18 ATSC digital broadcast formats, including 1080i and 720p. From there, the TV set manufacturer determines what format the sets use for display.

It is, in part, a numbers game. 720p provides 720 vertical lines of digital video information on a screen, while 1080i provides 1,080 lines. But while both offer a much more detailed picture than analog TV's 480-line resolution, the schemes diverge when it comes to the way they refresh the image, and that's where the "p" and "i" come in.

"P" stands for progressive, and under this scheme, all of the lines of resolution are refreshed every 1/60th of a second. "I" stands for interlace, and under this scheme, half of the lines are alternately refreshed every interval. So lines one and three will be updated in one interval, followed by lines two and four in the next.
Which is better?
This combination of resolution and refresh is at the heart of the programmers' HD debate. And if you look at sheer numbers, the 1080i camp is in the majority, with all but ESPN and Fox Networks so far tapping the format.

HDNet's decision to side with 1080i was all about the resolution, according to HDNet President and co-founder Mark Cuban. "The more HD you watch, the more you notice the enhanced resolution. We get comments from viewers all the time commenting on how our picture is crisper than other broadcasts," he says.

But Fox Network doesn't see the picture the same way, announcing recently that it will begin presenting the bulk of its primetime programming in 720p. It also has sewn up a deal with Time Warner Cable to produce a number of sports events via Fox Sports Net in 720p.

As with other 720p supporters, the progressive scan was the deciding factor. The biggest problem Fox sees with interlace is artifacts–jitters in the image created by the alternating refreshed lines. That can be more pronounced in high action scenes, particularly in sporting events.

"It's difficult in a broadcasting environment to switch spatial resolutions, and 1080i being so inferior to 720p in terms of interlace artifacts–and if you watch 1080i sporting events, it really doesn't work," says Andrew Setos, president of engineering for Fox Group. Cuban, however, counters that with HD video now a reality, HDNet has had few problems with artifacts, even when dealing with sporting events. "In the rare cases where they occur, it's even rarer for the viewer to notice," he says.

If the quality debate is not entirely clear, why are most of the networks so far opting for 1080i? Setos says it comes down to marketing. "People are scared that the number 720 is smaller than 1080," Setos says. "It's like buying octane, buying high-test versus regular at the gas station, even though for most cars, high-test doesn't do anything."

Not everyone thinks 720p is best for sports, however. Cablevision Systems Corp. chose the 1080i format for its Madison Square Garden Network original HD content because "we happen to think it looks better in 1080i," says Wilt Hildenbrand, Cablevision's executive vice president of engineering and technology.

The mux mix
Quality aside, HD demands up to five times the bandwidth of standard digital signals, so cable operators are turning to outfits like Terayon Communication Systems Inc. and BigBand Networks Inc. for stat muxing systems that can fit more streams on the same 6 MHz channel. Both companies are seeing subtle differences when it comes to handling 720p versus 1080i.

In general, during scenes with not much action, both formats can be sculpted to cut down on the bandwidth without reducing the overall quality, says Sylvain Riviere, BigBand's director of product marketing for broadcast services. But in higher-action scenes, depending on the quality of the encoders used to format the video, "the bitrate of a 720p stream can certainly be accommodated around 13 (Mbps) more often than a 1080i would if you had a higher scene complexity."

One place where cable's dual HD format environment could face a snarl is in digital ad insertion. In particular, it is not clear what will happen if a digital ad shot in 1080i ends up inserted in a 720p video stream–or vice versa, says Mark Jeffrey, senior product line manager for Terayon's digital video solutions group.

"You could have issues moving toward ad insertion," Jeffrey says. "If you had a network feed in one format, and you have an ad that may be in another format, how is that handled down the line?"

Indeed, that is one reason Turner Networks decided to go with the 1080i format for its new TNT HD channel, set to launch in May, according to Mike DeHart, vice president of domestic distribution and technology for Turner Network Sales. The hazards created by switching between 1080i and 720p for either programming or ad insertion could literally leave a black mark.

"As far as the encoding and transmission process is concerned, we could technically use multiple formats, but this would cause consumer devices to momentarily 'black out' each time the format was changed, causing an interruption in our programming and unhappy customers," he says.

Programmers could get around the issue by filming versions of ads in each format, but that would be more costly for the ad sponsor and cable operator. "I would rather keep the content in one format–I don't want to have two camera crews and store two versions of the ad," Jeffrey points out. "I would rather have one."

Cablers are agnostic
Still, these issues are apparently not compelling enough to prompt MSOs to join the fray. For example, while Cablevision may have chosen 1080i for its own programming nets, it isn't requiring its network partners to do the same, Hildenbrand says.

So, too, is Adelphia Communications staying out of the format debate. Adelphia started deploying HD in July, and, at last check, had HD available in about 55 percent of its digital footprint.

It passes through the HD signals from programmers in their native formats, and all of the digital boxes in its offerings can render either format, according to Doug Ike, Adelphia's vice president of advanced video engineering and development. He notes, however, that the dual schemes do create confusion among subscribers, as they try to line up the signal formats between the box and the TV set.

"I think it is certainly a situation where it is a very, very confusing topic area to get all of the configurations set and really try to explain the various TV formats," Ike says. "But again, from a cable operator and from the perspective of the equipment providers–the Motorolas and the Scientific-Atlantas–all of these vendors are doing the multiple formats, and our goal is to pass through as transparently as possible native format to the TV device."

The fact the cable operators are not taking sides reflects the fact that for consumers, there also is no clear winner.

"For the average customer, you put them in front of a display unit that has 720p and right beside it is a display with 1080i and they can't tell the difference," says Mark Hess, Comcast Corp.'s vice president of digital television. "You've got to be someone who is [an] expert, and you have to be looking at it very closely to really discern the difference between the two. That's why it is easy for us to say whatever the content provider wants to do, we will live with, and our goal is to make sure it is easy for the customer to understand what he is getting."

Nor does Hess see any future where the cable operators would ask programmers to change their HD format to best fit a more constricted bandwidth pipe.

"We're kind of in a position where we're saying, hey, whatever you decide we are going to try to accommodate, assuming we have come to an agreement to carry your content. And then really our goal is to get as much of it on as we can and make it as easy as possible for the customer to use and see," he says.

[DeBelak]

From my understanding the tv stations are broadcasting in 520 lines of res.
One of my good friends is a tech for CBS