July 2006 Issue Advanced video coding offers improved compression, but there are some significant issues, such as random access points, DPI and DVRs, that need to be addressed before cable operators give it the podium. By Mike Robuck, Associate Editor There is an evolution underway with the adoption of the MPEG-4 based Advanced Video Coding (AVC) Standard by telco and satellite operators, but don’t expect cable to jump on the bandwagon any time soon. Sure, cable operators are attracted by the promise of a 50 percent bit rate reduction in compression from MPEG-2 to MPEG-4, which will save bandwidth, but there still needs to be a roadmap on how those efficiencies will be gained. And then there’s the not so small issue of what do with the existing 40 million plus legacy set-top boxes that are unable to handle MPEG-4. During the May CableLabs analyst briefing, Comcast CEO Brian Roberts said he believes in the coding development and that MPEG-4 AVC is “absolutely happening, and I think cable we’ll benefit from that” (improved compression). Roberts also said one way of gaining additional miles from the legacy set-top boxes would be to have them deployed in secondary rooms in homes. “We’re looking at them (AVCs), but we don’t have any immediate plans to deploy them,” says John Hildebrand, Cox‘s vice president of multimedia engineering. “We have some visions of how we think advanced codecs will be used over time, and we’re just encouraging our vendors to think about doing that.” Telcos using twisted copper have no choice but to use MPEG-4 in order to deliver their video services, according Nimrod Ben-Natan, vice president of solutions and strategy for Harmonic. Both Verizon and DirecTV, as well Internet protocol TV (IPTV) providers, have committed to using MPEG-4, although the latter have been slowed by the lack of IPTV set-top boxes. “Pretty much the same goes for the satellite guys in the United States who are rolling out high-def in MPEG-4,” Ben-Natan says. “At the same time, and this is true for both telco and satellite, the installed base of HD MPEG-2 boxes was close to zero, so there was no legacy consideration at all. “When it comes to cable, that’s a bit trickier. I think for the cable guys to migrate from MPEG-2 to MPEG-4, it’s going to be painful. There are a couple of options, but none of them are simple because of the huge installed base of HD MPEG-2 set-top boxes.” MPEG-4 AVC’s lineage dates back to 2000 when MPEG-4 was adopted by the International Standards Organization. MPEG-4 AVC came about through the combined efforts of International Telecommunications Union and ISO/MPEG, which formed a joint video team. The result was the creation of ISO/MPEG MPEG-4 part 10 and H.264 in ITU in 2003. By contrast, MPEG-2 was born in 1994, but Dr. Yasser Syed, CableLabs’ project manager, streaming media technologies, says MPEG-4 is designed to do much more than broadcast digital audio and video to homes. “The AVC standard is trying to be a standard across industries,” says Syed, who chairs the SCTE‘s advanced video coding group. “It was developed in light of the broadcast industry, in light of the streaming industry and in light of the IP industry. When MPEG-2 came out, you didn’t have all of these other applications. Even in cable alone, we started out in broadcast, but now we have all of these applications and services going on like VOD (video on demand), IP, ad insertion, and PVRs (personal video recorders). “What we’re doing in the (SCTE) advanced video coding group is dealing with issues about how to develop a constraints document that considers all of these applications and tries not to bound the future.” Aside from the improved compression, the benefit of MPEG-4 is that is used in a variety of applications across several industries, including the consumer electronics industry. But Syed says the challenge is making MPEG-4 AVC, which wasn’t designed just for digital broadcast like MPEG-2, work in the cable environment. MPEG-4 needs to work in the existing MPEG-2 structure, and Syed says the AVC toolbox “allows you to mimic the MPEG-2 model.” The existing MPEG-2 transport can carry packets, but instead of carrying MPEG-2 video type information, it will be able to carry AVC type information as well because of the packet identifier (PID). The PID can identify a subset of transport packets in the transport mux that belongs to a video stream instead of an audio stream or data stream. Along with this a stream type identifier will indicate that it is MPEG-2 or AVC (MPEG-4 AVC) stream, says Syed. Some of the challenging areas for implementing MPEG-4 include random access points in video streams and digital video recorders (DVRs) and digital program insertion. “The random access point in dealing with channel change, that’s a pretty significant thing to work out,” Syed says. “That’s a critical element in there because it affects something akin to the GOP (group of pictures) structure, and it also highly affects your compression efficiency. That’s stuff you use for channel changing and stuff you use if you’re trying to surf in a DPI (digital program insertion) type situation. Also, PVRs use that to do things like trying to get into the video stream once they’re out of it, so it’s kind of a mixing point there as well.” MPEG-4 also needs to work with existing functions such as emergency alert messages and electronic program guides (EPGs), while audio/video synchronization needs to be maintained and agnostic to a new AVC standard. While the 50 percent compression savings in MPEG-4 is often bandied about, Grass Valley Director of Marketing Jean Macher says it’s not quite there yet, and it depends on factors such as statistical multiplexing and preprocessing. “Typically today, the MPEG-4 in SD (standard definition) is in the 1.5 Mbps to 2 Mbps range, so it’s not 50 percent yet,” he says. “For HD, it’s more in the 9 to 10 Mbps range, but I’m talking mostly CBR (constant bit rate) here. If you do stat muxing you can lower that, of course, and the more programs you have, the more you can lower the average bit rates.” Syed says cable operators might have to trade off some of the compression efficiency in order to support the existing services and experiences. “Things like random access point or channel change affect the compression efficiency because it kind of defines your GOP structure,” he adds. Driving the transition While hurdles remain for cable operators, that’s not to say they’re not casting a keen eye on MPEG-4. Thus far, the only real public announcement from a major U.S. cable operator on AVC was back in January at the Consumer Electronics Show when Comcast said next year it would buy 200,000 of Samsung‘s advanced set-top boxes, with an option to purchase 500,000 more, and as many as 1 million set-top boxes from Panasonic. The boxes will be used for Comcast’s real next-generation (RNG) initiative, which is based on the OpenCable Application Platform (OCAP). The Samsung boxes will fill Comcast’s RNG 100 level, and the all-digital boxes support both MPEG-2 and MPEG-4/H.264 AVCs. The Panasonic RNG 200 set-top boxes, which also support OCAP, will decode both MPEG-2 and H.264, along with having HDTV tuners. By using MPEG-4 for the encoding, Comcast could send on demand video streams to customers at lower bit rates than MPEG-2, and if the conditional access rights were in place, they could download those streams to other devices. Comcast CTO David Fellows said in a recent CableWorld interview that MPEG-4 or Microsoft‘s VC1 encoding would help his company take advantage of hundreds of on demand HD movies and HD channels, in addition to today’s MPEG-2 offering. CEO Roberts said the beauty of the RNG set-top boxes with AVC is that they can grow with increased amounts of HD offerings and channels. Marty Stein, Motorola‘s senior director of marketing for Connected Home Solutions, points out that cable operators can keep themselves busy saving bandwidth by implementing switched digital video (SDV) before adding MPEG-4 AVC in a few years. But he believes more HD channels and HD VOD will drive the transition to MPEG-4 AVC. “With HD VOD, you’re looking at a higher tier of service that could offset the price of new set-top boxes for those customers,” Stein says. “You wouldn’t need to worry about recouping your costs with that kind of swap-out.” Chris Gordon, EGT‘s director of product management, says OCAP and increased sales of HDTV sets will also drive the move to AVCs. “They’ll (cable operators) start the set-top box conversion with HD and, as time and budgets allow, include SD, but from their perspective, the boxes that will be deployed or purchased will do everything else like MPEG-2, SD and all of the flavors of codecs,” he says. “I think there’s a forgone conclusion from all of the operators that one day they’re going to MPEG-4.” And as Stephen Goldstein, senior business development manager for Samsung Electronics Americas, points out, many major chipset manufacturers plan to bring out integrated silicon for MPEG-4 decoding this year. While Goldstein wouldn’t comment on Samsung’s plans, those same silicon chips could end up in TV sets as well over the coming years. “I think you’ll see a steady growth of customer premises equipment (CPE) and set-top boxes that can decode AVCs over the next three years,” he says. “That trend will not go away, and it will only grow for all of the logical bandwidth reasons.” While MPEG-4 may not be a varsity player just yet, it can have a supporting role in the near term by providing services such as picture-in-a picture streaming that is overlaid in set-top boxes for mosaics. Another possible application is broadcast-quality TV to PCs using the low bit rates of MPEG-4 over IP. USDTV ready for MPEG-4 U.S. Digital Television says it will become the first broadcast service provider in the United States to convert its entire network from MPEG-2 to MPEG-4 AVC encoding this summer. USDTV is an over-the-air terrestrial digital subscription TV service that currently operates in four markets. USDTV started out its service by encoding MPEG-2 in its network operations center (NOC) in Salt Lake City. From there, the signals were delivered to MPEG-2 set-top boxes in customers’ homes. USDTV will use Tandberg‘s end-to-end broadcast encoding systems based on its MPEG-4 AVC SD compression technology. Richard Johnson, a co-founder of USDTV and current COO, says the cable programmer feeds will be taken down to baseband before being re-encoded in MPEG-4. The MPEG-4 video signals will be transcoded by a matchbox-sized dongle, which is plugged into a universal serial bus (USB) port in the set-top box, back to MPEG-2. With the dongle, USDTV doesn’t need to worry about replacing the legacy MPEG-2 boxes, but it does plan on releasing an MPEG-4 box later this year. The new boxes will also have MPEG-2 to be able handle local broadcast channels that aren’t in MPEG-4. Johnson says converting from MPEG-2 to MPEG-4 with the dongle was part of the company’s original strategy, and the MPEG-4 boxes will allow it to deploy VOD. “By moving to MPEG-4, we gain more spectrum and two benefits,” he says. “The first is that we’re able to use the recaptured spectrum for linear services, and the second is that we’ll be able to offer more relevant bits of quality. We can actually improve the quality of the video signal by moving to MPEG-4.” MPEG-4 gaining momentum John Morrow, Scientific-Atlanta’s vice president and general manager of headend systems, says, “the important thing is that MPEG-4 is being validated,” in the real world today by telcos, IPTV and satellite operators. Currently, most video signals are still in MPEG-2, but content delivery companies such as SES Americom are using S-A’s encoders for MPEG-4 while programmers could also jump on the compression saving bandwagon. “The technology is the same whether we’re encoding for telcos or cable,” Morrow says. “Cable can look at the bandwidth savings, storage savings and the new applications, with the digital rights management in place, for customers. I think cable is pretty excited about the technology.” Mike Robuck is associate editor of Communications Technology. Reach him at [email protected].
Sidebar 1 “The AVC standard is trying to be a standard across industries.” Dr. Yasser Syed, CableLabs