Peering beyond MPEG-2
With HD and video-on-demand starting to load up cablers' spectrum, the industry is starting to look beyond tried-and-true MPEG-2 to advanced codecs able to pump out better sound and pictures at lower bit rates. But while many technical minds say it is more a matter of if rather than when, the road to an advanced codec-driven cable system has more than a few major potholes.
Windows Media 9 Video, used to encode IMAX's
Coral Reef Adventure for a DVD PC release,
could offer cable operators HD picture quality
at much lower bit rates compared to MPEG-2.
The biggest argument in favor of these new codecs, including MPEG-4/H.264, Microsoft Corp.'s Windows Media 9 and RealNetworks Inc.'s Real 10, is that they make traditional MPEG-2 look like an obese bandwidth hog. Depending on the encoding and resolution used, an MPEG-4 HD video stream can transmit at about 6 Megabits per second, compared with standard MPEG-2's 19.4 Mbps. RealNetworks Inc. claims that its new Real 10 video codec can deliver HD streams at 5 Mbps, and Microsoft estimates its Windows Media 10 can deliver a 1080p HD video at 6 Mbps.
Cutting the bit rate per video stream is an attractive prospect for cablers, because it could allow them to scale those systems up and use the same bandwidth to reach more customers with more content at a lower cost.
"If I can decrease the number of bits by a factor of three, I decrease my cost by a factor of three," says David Fellows, Comcast Corp.'s chief technology officer. "So for that and a whole bunch of reasons– keeping costs down and increasing the variety of programming–we think that advanced video codecs are a very important part of our future."
But which advanced codec will become part of that future is still a tossup. Among the myriad codecs in play, the front-runners appear to be MPEG-4/H.264 and Windows Media 9.
In its broadcast video incarnation, MPEG-4 goes by names including H.264 or MPEG-4 Advanced Video Codec or MPEG-4 Part 10. They all refer to a standard that emerged from the Joint Video Team (JVT) of the International Telecommunications Union and International Standards Organization. The JVT created an amalgam of two standards, welding MPEG-4's multimedia capabilities to the H.264 videoconferencing standard's compression technology.
Chief rival Windows Media 9 debuted about a year ago, and while it is a proprietary scheme, it gained strength when Microsoft submitted it to the Society of Motion Picture and Television Engineers as an open standard.
"Without this, nobody would be considering Windows Media," says David Price, VP of business development for Harmonic Inc.'s convergent systems division. "If they hadn't done that–if they hadn't opened up the specification to SMPTE–they would not have been taken seriously."The race
In the past, such a horse race has favored the standard, but in this case there is an added complication: a complex and controversial proposed licensing scheme for the MPEG-4/H.264 technology that includes a per-stream usage fee. Given the high number of video streams needed for a VOD service, that could be particularly disastrous.
"Picture the reporting infrastructure I need to put in place just to collect the money it is that I owe," Fellows says. "Forget my philosophical disagreement with the concept of usage-based royalties–the reporting infrastructure is a huge hurdle."
Microsoft, meanwhile, has eliminated some of its traditional codec license restrictions for Windows Media 9. It also has moved to lock the decoder portion of the codec, giving chipmakers and hardware vendors assurance that there will be periodic new versions requiring product upgrades, according to David Caulton, group product manager for Microsoft's digital media division. "As a result, we actually have gotten a number of the circuit manufacturers and programmable DSP manufacturers lined up," he says.
But there is still a lingering wariness of the software giant.
"I think that there would be one if there was a clear winner from a royalty perspective," says Brian Sprague, director of Broadcom Corp.'s marketing broadband business group. "And I think Microsoft has thrown out some good proposals on licensing Windows Media 9, but I think the world is somewhat afraid of giving that much power to Microsoft. I think there will be markets for both, and you want to be able to support both."
Harmonic sees that as well, so its upcoming line of encoders will be capable of dealing with H.264, Windows Media and MPEG-2 to give programmers ample choice.
"So we really are just trying to give the industry an insurance policy, so they don't have to worry," Price says. "Whichever proves to be the most suitable, they can simply flick the switch at both ends with simple software. The actual user won't know the difference, that one day they are watching Windows Media and the next day they are watching H.264."The install base
But even if cable operators do bite on advanced codec systems, the bigger hurdle will be getting them into the field, and that starts with developing the silicon. Work is under way to create the silicon decoders for digital boxes able to render MPEG-2 and MPEG-4 or Windows Media 9, but thus far, there is not a chip to do all three. Meanwhile, Cablevision Systems Corp.'s Voom satellite TV service is using Motorola Inc. digital boxes equipped with an MPEG-4 decoder expansion slot, so in the future, it could switch from MPEG-2 to MPEG-4/H.264.
Broadcom hasn't announced any silicon based on MPEG-4 or Windows Media 9, but Sprague notes that any chipmaker in the satellite or cable industries has to be working on it.
Cable operators, meanwhile, are feeling the pressure to move quickly, given the prospect of increasing HD and VOD bandwidth loads. Comcast is trying to get advanced codecs into its set-top boxes within two years, Fellows says.
"I guess I would say right now that we have not specifically required in writing an advanced video codec in a set-top, but it's absolutely under discussion with all of them," he adds, noting the Voom upgrade slot was an interesting idea. "So if we can't actually get the codec fast enough, then maybe there is an upgrade path that we can allow."
Once those boxes are ready for rollout, operators will face a bigger hurdle: deploying service using these new codecs while dealing with the legions of MPEG-2 digital set-tops already deployed that cannot be upgraded.
With a mix of legacy and advanced codec boxes, the likely scenario involves introducing advanced-codec systems first with new HD and VOD rollouts, while maintaining the traditional MPEG-2 system for traditional cable TV service. MSOs could do so by dedicating a block of QAM channels for content broadcast using advanced codecs to new customers, even while maintaining MPEG-2 VOD service to existing subscribers, Sprague says.
That does require two sets of content, "but when you look at the arithmetic on how many more VOD services that they could provide with the lower bit rate, then they are pretty enthusiastic about doing that," Sprague says.
Fellows also sees a migration starting with a mix of MPEG-2 and advanced codec VOD content, allowing the natural process of box attrition to increase the new system's foothold. "And so over time, I can deploy more and more advanced codec set-tops and more and more of my infrastructure is streamed out at the lower bit rate," Fellows says.
Telco and satellite competitors are also delving into advanced codecs, and may get to market sooner than cable, Sprague notes.
"The big picture is that it is going to be deployed in all markets–I think the question is time frame," Sprague says. "If we are talking in long durations of time, like five years from now, I think there is going to be a pretty big penetration of this technology into all of these markets."