A recent announcement from Harmonic about the introduction of a new-generation HD encoder using MPEG-4 AVC H.264 compression promised new efficiencies in video compression that would make delivery of high-definition television practical for IPTV service providers.
According to the company, the Electra 7000 can solve the problem of delivering HDTV service via existing telco infrastructure as part of an IPTV service offering while maintaining a level of quality that will produce customer satisfaction.
IPTV Update spoke with Arnaud Perrier, Harmonic’s senior product marketing manager for HD and advanced encoding products, about the Electra 7000 and how it’s achieving these efficiencies.
IPTV Update: A recent Harmonic press release says the Electra 7000 HD encoder can achieve a 20 percent to 30 percent bit-rate reduction over the results of other MPEG-4 H.264. How?
Arnaud Perrier: There are different elements to this product that are disruptive in terms of technology and its architecture. One of them is that unlike the first generation of high-definition AVC encoders out there, we’ve gone to mostly an ASIC implementation. Many of the standard functions, for instance transform coding or CABAC, require intensive processing. Traditional DSP or FPGA architectures require a lot of complex chips to do that. Now these standard functions are basically hardwired in a very small IC. That frees up a lot of processing power and cycles in the rest of the architecture to customize tools that actually make a difference in terms of video quality. Those are things like rate control, motion estimation search, mode decisions and others.
The second important aspect made possible by this architecture is single-slice video encoding.
IPTVU: Could you describe single slice video processing?
AP: The fact that we use this groundbreaking ASIC architecture, which is technology that did not exist six months ago, allows us to not only go to smaller form factors and be more efficient, but also allows for one of the first times in this industry to do single slice processing for a high-definition picture. Up to now, MPEG-2 products and competitive H.264 products have used multiple slices to process the picture. In other words, a picture is broken down into six or more horizontal slices and those are each processed in parallel due to compute power and interconnect computing limitations.
The limitations of those architectures are pretty simple. Excellent motion estimation is challenging and multi slice also limits the range of your motion search and motion vectors. Typically, those are limited by the vertical size of your slices. That also impacts your ability to do an efficient deblocking filter.
Basically, the net result is you typically will see artifacts, especially on vertically fast motion and panning motion pictures, so of course you have to run at higher bit rates as a result.
With the Electra’s single slice architecture, we process the entire picture at once in a single frame and that has a lot of benefits.
IPTVU: Your press release also said the Electra 7000 uses full multi-pass look-ahead encoding to reduce bit rate. Could you explain?
AP: So far, existing architectures have been either single pass or at best one-and-a-half pass. In other words, original architectures would not fully encode a picture and derive statistics from the MPEG-4 encoded picture before doing the second pass. They would tend to look at the original uncompressed picture or even worse, at MPEG-2 type statistics. This created discrepancies between your LookAhead statistics and what you are about to encode. We pushed the envelope a little more by adding an entire stage of LookAhead encoding. In other words, we are going to encode each frame fully in high definition H.264, look at those statistics before and after encoding and then use that for what we call the master encode downstream.
This process gives you much more refined and accurate statistics and better compression efficiency.
IPTVU: You also mentioned the use of advanced video pre-processing. Could you explain?
AP: We aren’t just stopping there. So far the early generation HD H.264 products have had shortcuts and tended to have limited processing — typically horizontal filters and basic temporal filters. For some products, even nothing. With this product, the Electra 7000, we are putting the emphasis on feature fullness and video quality as people have come to expect in the MPEG-2 world.
So we are supporting MCTF — motion-compensated temporal filtering. That’s basically an advanced temporal filter that takes motion vectors into account to adapt the level of filtering in the picture. And that significantly reduces the amount of motion artifacts on difficult scenes such as sports and on noisy sources; it will clean out a lot of the mosquito noise and film grain.
IPTVU: How important are these measures and consequent bit rate reductions to IPTV operators wishing to offer HD service over DSL lines?
AP: I think IPTV is the space that will probably benefit most from this new product. Of course, the satellite customers are always happy to get any bandwidth gains they can. But specifically in the IPTV space what this means is a lot of services previously thought to be borderline or impossible with telcos on xDSL networks are now possible.
A lot of shortcuts have been taken by IPTV operators so far and things like pair bonding on ADSL networks to be able to double the capacity and actually make HD service available to all customers, even those who are far away from the central office.
The bottom line is when you have 20Mb/s to 25Mb/s available to three TVs in the house, one high definition and two standard definition, and you want 6Mb/s data traffic on top of that, it means you have 7Mb or 8Mb available for your HD service in the best case. So far the technology has really allowed something like 8.5Mb/s, which is borderline and why a lot of operators like AT&T have not deployed HD yet.
What that means in a nutshell is up until now, 8.5Mb/s HD either required pair bonding for those subscribers at the far end of the local loop, or for some companies required format conversion from 1080i to 720p, which is hurting the consumer experience and also means telcos are losing their competitive edge versus cable and satellite. Now, what the Harmonic Electra 7000 means to them is that instead of 8.5Mb/s, we are talking an equal or better quality level for high definition with pristine pictures at 6Mb/s or below.
That is huge for telcos because that means now no more conversion to 720p, no more need to cut the resolution, and especially no more need for pair bonding, which is a significant cost savings. And that means dual HD service in some cases, i.e. watch and record PVR functions — something they haven’t been able to offer.
IPTVU: Could you discuss audio?
AP: The Electra 7000 is a multichannel audio product. Most high-definition encoders out there simply pass through 5.1 audio. Our new product is capable of encoding AC3, Dolby Digital Plus, and AAC/HE-AAC 5.1/7.1 onboard. For operators, that translates to cost savings in the architecture and fewer points of failure.
IPTVU: Is there anything else you would like to add?
AP: Of course, the emphasis is on the low bit rates and the level of picture quality, but it also is breaking ground in terms of density, which is important for operators. For telcos, the ability to have four channels and picture in picture channels, which is eight total in a single chassis is huge in terms of CAPEX and OPEX. And if you take the four-channel configuration, that’s basically eight times the density of what is deployed today.
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