HDTV & VOD: A Match Made in Heaven


The rapid interest in developing and deploying HDTV — coupled with the cable industry's push to launch video-on-demand — has created strong interest in marrying the two technologies and services.

Cable operators are moving towards adding HDTV content to their VOD servers, combining two leverage points against direct-broadcast satellite into a single service.

HDTV on VOD was barely mentioned at the 2002 National Show. This year, however, VOD vendors were handling numerous inquiries from operators about making their on-demand systems HDTV-ready.

And, on the last day of the show, Cablevision Systems Corp. announced it would launch HD on VOD later in the summer.

"We are very pleased to be able to add high-definition content to the broad mix of programming that we are offering our Interactive Optimum customers on-demand," Cablevision president of cable and communications Tom Rutledge said at the time, "particularly since it builds upon the tier of HD networks we have already introduced."

Said nCUBE Corp. president and CEO Mike Pohl: "There is a lot of interest around HD. We're a big proponent. We're perfectly capable of ingesting HD, and there is plenty of room for storage."

Aside from Cablevision, "there is an excellent likelihood you'll see some beta sites before the end of the calendar year," said Bob Chism, chief technology officer of Concurrent Computer Corp. "Our two biggest customers are very interested and have plans, and have asked us to support activities that will support rollout of HD services."

The addition of HDTV content affects the entire VOD platform to some degree, but the biggest issues are storage and transport. VOD content is typically encoded at a rate of 3.75 Megabits per second.

HDTV content encoding can range from 14 to 19 Mbps, which means that an HDTV movie can take up four to six times as much storage space on a server as a standard-definition movie.

The same extrapolation occurs on the transport side. A typical quadrature amplitude modulation device can handle 10 VOD streams simultaneously. The same QAM could handle only two VOD HDTV streams.

In both cases, operators have to decide how much storage to add to VOD servers to handle HDTV content, and how to reconfigure or add QAMs to handle HDTV transmissions.

Cablevision declined further comment on its HDTV VOD plans. But server vendors — including SeaChange International Inc., Cablevision's server provider — said they're currently testing HD content on VOD systems with an eye towards rollouts by year-end.

"We started work a while ago," said SeaChange corporate vice president of strategic planning Yvette Kanouff. "The first hurdle we had to overcome was to look at encoding compatibility.

"We had built a standard-definition encoding standard and in HD, we have to do that all over again. There still is not a standard HD spec."

As result, she said there is much encoding, testing, re-encoding and retesting going on. Feedback is being shared among content providers, MSOs and equipment vendors.

A second key question: How will HD VOD affect on-network bandwidth and the mixing and matching of standard-definition content and HD fare?

"Does HD have its own, dedicated channel, or do you share bandwidth?" Kanouff asked. "Do you give dedicated QAM bandwidth to one versus the other?

"Now the bit rates come into effect. We're looking at all that and testing that with different outputs."

Solving the engineering questions depends somewhat on clarification of the business issues.

"How much HD content do you want to offer, and what are price points?" Kanouff asked. "That's still a general unknown. How much HD content is available and how does that correlate to usage, churn reduction, digital penetration? That's probably going to be at the tail end of all those things.

"We have to figure out what the right balance is. Some things are just fine in standard definition."

Kanouff said the storage upgrades "are pretty straight forward and standard."

SeaChange currently deploys 140-Gigabit disk drives, with Moore's Law working in everyone's favor. Every year, more storage capacity can be added to existing rack units without increasing the space dedicated to servers, making it easier to think about adding HD content to existing servers.

"The performance has grow quickly," she said.

As for Cablevision, Kanouff said: "We've gone through the work of qualifying our systems. It's a matter of getting the content and which content providers are ready for HD. It's very feasible to launch this year."

SeaChange also has been testing HD VOD transmissions through for ASI and Gigabit Ethernet outputs, the latter which Cablevision uses.

"Time Warner Cable has talked to nCUBE about HD," Pohl said. "We could handle HD tomorrow. All the servers are out there. The products we're making are all backwards-compatible.

"It's going be an interesting time. We are better positioned that we ever have been to offer them what they want."

And the new combined HDTV/DVR boxes will only increase interest in high-definition VOD, he added.

Joe Matarese, director of solutions engineering for nCUBE, said: "We've always been highly focused on scalability. How do we store content in the most efficient manner? How do you build a server that can supply in a centralized environment GigE transport to a whole metro area?

"With HD, the importance of scalability is really being emphasized. We can support 60,000 streams on a single server of standard definition content. We support 170,000 hours off of single server. I spent a lot of time in translating those numbers into HD numbers at NCTA."

nCUBE has being testing HD content, and working on the storage and output issues, while working through some unknowns. "What is the right business model?" Matarese asked. "Can you charge more for an HDTV movie?"

"Operators want flexibility to not have to build a separate overlay network. Do they want to send HDTV VOD down the same QAM channels that are feeding all three service groups?" he asked.

nCUBE is working on software to allow MSOs to mix SD and HD streams on the same QAM, or to dedicate QAMs entirely to VOD, for instance, during a busy VOD time period, like Friday nights.

If a node has four QAM channels, an operator could fit 40 standard-definition VOD streams into that grouping. HD VOD may force operators to add QAM channels, perhaps to eight or even 16, Matarese said. Comcast's plans to recapture analog bandwidth and perhaps go to an all-digital network would open up QAM channels for both HD broadcast and HD VOD. "It's all about reallocating spectrum."

Matarese said the nCUBE servers used by Time Warner can handle several thousand streams each.

"Our servers have building blocks and certain numbers of disks and streaming capacity. We link all that together and make it one video server. Content gets stripped across all the disks," he said.

By adding a rack of medium hub units, Matarese said, TWC could double its storage and streaming capacity for HD VOD.

Ingesting HD VOD content is not that difficult, Matarese said. "It just means we're having to ingest more bits." The increasing shift to store content centrally at a headend means "you simplify your ingestion. You have to get it from the staging server onto the streaming server and you do that once. You don't have to take that content from the docking station to one server and then to 10 to 15 servers."

HD content for VOD may be encoded at different bit rates, even below the 19 Mbps that's standard for HD broadcast stations, which would save storage and streaming space. Sporting events, like hockey, may be encoded at higher rates, while movies without a lot of action could be encoded at lesser speeds, perhaps in the mid-teens, vendors say.

"I've heard 14.4 and 16, and even as low as 12," Concurrent's Chism said. "There are decisions still to be made there. Operators are trying to pick the right bandwidth and bit rate to give them most optimum use of the system," he said, even to the point of trying to get a third HD stream into a single QAM.

Chism said storage is not a problem for Concurrent. "We saw huge growth on the storage side of things with SVOD and FOD," he said. "Our systems easily allow for independent storage expansion. We're seeing above 2,000 hours being requested on these systems."

Chism believes it will take some time for MSOs to license enough HD content to tax VOD server systems. "Let's say they settle on the 14.4 megabit number for encoding," Chism said. "They can fit two HD and two standard definition streams through a single QAM. This will increase storage some. Our systems are designed to add storage and grow systems as HD comes on."

"We can do ASI or GigE," he added. "You can add independently more streaming units if you will. They can handle either the ASI or GigE. Anymore, all we ship going forward is GigE."

Chism said Concurrent is working with encoding houses to validate different bit rates on its servers. "Then we'll deliver HD capable servers to various cable operator labs. The baseline software and the entire HD baseline will be validated, made ready and be delivered."

"Each server vendor will be using their algorithms to load balance the best combination of standard definition and HD. They want sophisticated algorithms that best fit standard definition and HD in QAMs to optimize the bandwidth," Chism said.

It's clear from vendor testing schedules that HD VOD is just around the corner. "We showed HD a year ago and people came and said: 'That's nice,' Kanouff said. "Compare that to this year and everybody said: 'I'm glad you're doing that.' It has changed significantly."

"We'd love to see this happen as fast as possible," adds Matarese. "There's no showstoppers there at all."