Comcast Media Center Readies for HD Influx


Englewood, Colo.— It got its start just as cable entered the digital age, and now it is preparing for an even bigger change in the picture, thanks to high-definition TV.

As the satellite origination facility for some 80 cable networks, as well as a center for video production and post-production, the Comcast Media Center in Englewood, Colo. — formerly the AT&T Digital Media Center — is increasingly on the front lines as HD encroaches onto TV's programming lineup.

That presents more than a few resolution challenges, but it also brings some clear opportunities, according to center vice president Gary Traver.

HD video really came into focus for the Comcast Media Center this summer, when an independent movie company shot, edited and produced a project there using high definition, 24-frame-per-second film. Just recently, the center assembled its first high-definition video-editing bay.

"We were contacted by a moviemaker, and that's how we got it in," Traver said. "A lot of our clients are production companies, and they are increasingly being asked to do this, so we are just responding to our customers."

On the transmission side, the center recently transmitted the National Basketball Association All-Star Game in high-definition format.

To do so, the CMC took the existing NBA signal multiplex carrying eight feeds and rejiggered the them, whittling down seven of the feeds to simple static screen placeholders and shifting the bulk of the available bandwidth into one HD stream.

That's a preview of what many networks may do further down the road, as they begin to experiment with HD programming, Traver said.

"What I found interesting was we could use the existing cable multiplex to do this, with no added infrastructure," he said.

Traver expects more HD demands from In Demand, which has announced it will start offering high-definition video-on-demand titles starting in April. The pay-per-view and VOD programming provider also has several HD special events planned for this year.

Bandwidth burden

Nonetheless, the task of encoding and transmitting HD is not without its burdens. One of the biggest issues surrounding HD these days is the heavy bandwidth load it brings.

While a standard-definition TV signal that takes up about 3.7 Megabits per second of bandwidth, a full-strength HD signal in 1080i resolution comes in at a whopping 17.9 Mbps.

In a cable system that transmits signals using 256 quadrature amplitude modulation (QAM), each 6-Megahertz channel can carry about 38.7 Mbps, so that means at the most only two HD signals can fit on each channel, with maybe some room left over for a small standard definition signal.

But there may be a way to get more HD out of that signal without the viewers ever noticing a difference, Traver noted.

By cutting down the 1080i resolution format to 75 percent and using some statistical multiplexing, three HD signals could be fit onto the same channel.

"We don't necessarily have an opinion on this, but it is interesting — if you look at commercial TV out there today, only the super-high-end TVs come anywhere close to displaying full 1080i," Traver said.

If shown a screen with full 1080i HD and a version at 75 percent resolution, "I bet you can't pick out the difference, because the sets aren't exploiting the full signal."

At present, the only network originating from the CMC with a channel devoted to around-the-clock HD is Discovery HD Theater. That service required a special HD control room, the first assembled at the CDC. As such, it provided some useful early lessons – including the fact that the technology is still fairly young.

"People are still trying to figure out how to do HD."

On the surface, it might seem an easy transition — take an existing digital encoding unit and swap in an HD encoding card and an HD playout card.

Not so. The CMC quickly found out that the integration with the other processing gear — including file decks, ad inserters, signal alignment processors, playback machines and so forth — wasn't nearly as straightforward.

"You would think all of those devices plug and play," said Traver. "They don't."