Cable is facing a bandwidth squeeze. As more and more channels go HD, cable is struggling to find the bandwidth necessary to carry them. There are four major ways cable systems can address the issue:
- Drop analog channels and reuse the frequencies for digital channels, including HD.
- Use Switched Digital Video (SDV) to only transmit content when required.
- Upgrade older 550MHz, 650MHz, or 750MHz cable systems to 860MHz or 1GHz infrastructure to increase the available bandwidth.
- Update the codec used from MPEG-2 to an advanced codec, such as MPEG-4 AVC/H.264, to reduce the bandwidth required per channel.
Cable networks have already been migrating analog channels to the digital tier, and some cable systems have already go all digital, but there is a large installed base of analog cable users on many networks. Cable MSOs need to take that into account, because upsetting their customer base by pulling their channels or forcing them to rent and STB can drive them to the competition. The switch to all digital is inevitable, but it may take years.
Switched Digital Video is already in use by a number of cable MSOs, with Time Warner notably deploying it widely and continuing to increase their use of the technology. All of the cable MSOs are looking to SDV to help alleviate bandwidth issues. SDV, of course, has conflicted with CableCARD. The Tuning Resolver will finally address that early next year. And SDV isn’t a solution for all channels, it is only effective for channels that are not in high demand.
Upgrading the cable infrastructure is certainly a good solution. The high end of cable systems today are 1GHz systems, though 860MHz is much more common for modern systems. But there are still many cable networks using older hardware with less available bandwidth. While these systems will almost certainly be upgraded during regular periodic maintenance, it is very expensive and time consuming. Not only the head end must be updated, but repeaters, etc, all through the network need to be upgraded. And the STBs used in the network must be capable of handling the higher frequency band. Due to the cost and complexity of upgrading the network this isn’t a quick solution.
And, finally, there is the option to update from MPEG-2 to an advanced codec such as MPEG-4 AVC/H.264. Using H.264, cable networks can roughly halve the bandwidth required for each channel – allowing them to carry twice as many channels in the same bandwidth. As you might suspect from the subject of this post, this is the latest direction the cable industry is headed. The satellite industry has already gone in this direction, with DirecTV and DISH Network both using MPEG-4 for their new HD channels.
As Multichannel News reports, The Society of Cable Telecommunications Engineers recently released a specification, SCTE 128 AVC Video Systems and Transport Constraints for Cable Television (PDF), describing the use of the H.264 codec on cable systems. To give you an idea as to the type of document this is, here’s the opening scope paragraph:
This document defines the video coding and transport constraints on ITU-T Rec. H.264 | ISO/IEC 14496-10 [5] video compression (hereafter called “AVC”) for Cable Television. In particular, this document describes the transmission of AVC coded video elementary streams in an MPEG-2 service multiplex (single or multi-program Transport Stream).
Yes, I read the document. Yes, I’m a geek, and it still almost put me to sleep. I find it interesting that the specification has features specifically designed to support DVR utilization, especially Appendix B“Encoding Guidelines to Enable Trick Play Support of AVC Streams (Informative)”. Actually, that appendix is kind of interesting on its own as it first covers how DVRs exploit MPEG-2 today for trick play modes, before going on to recommend how to achieve the same functionality with MPEG-4. OK, I thought it was interesting.
The cable industry is already beginning to use MPEG-4 for content distribution to the head end, but service to the home is still MPEG-2. The problem with switching to MPEG-4 is, of course, that you need devices that support MPEG-4. Most of the STBs currently deployed are MPEG-2 only. So, as with the satellite industry, the move to MPEG-4 will require deploying new STBs. This will happen organically as STBs wear out and are replaced by cable MSOs periodically anyway, and MSOs can select STBs that handle MPEG-4. As the Motorola-related blog Media Experiences 2 Go (formerly Connected Home 2 Go) posted yesterday, cable MSOs will likely start using MPEG-4 in their higher-end content tiers. In this way they could deploy MPEG-4 capable STBs to only the users who require them at first, giving them more time to expand deployment before cutting over lower content tiers to MPEG-4. This is very similar to what the satellite companies are doing, using MPEG-4 first for new content so that existing users can continue to use their MPEG-2 STBs until they wish to adopt some of the new services. This avoids requiring a mass swap-out of STBs. Motorola VP Geoff Roman had this to say:
On the cable side, you’ll start seeing MPEG-4 devices (CPE) early next year, with gradual phasing in of more MPEG-4 hardware throughout 2008. Operators will incorporate MPEG-4 in their highest service tiers first, moving to mass distribution of MPEG-4 set-tops by late 2009, early 2010. By the latter part of 2009, MPEG-2 standalone devices will have completely disappeared.
So this is no big deal for those who uses a cable provided STB – you’ll simply get a new STB from your cable provider. No muss, no fuss. But what about other devices? What about clear QAM tuners? What about CableCARD devices? Well, if they don’t have an MPEG-4 decoder they’re simply out of luck. They will not be able to tune the new content, period.
The good news is the TiVo Series3 and TiVo HD both have decoding hardware that can handle MPEG-4 AVC/H.264 (and VC-1/WMV). While it isn’t currently enabled, it will just take a software update to enable them. So these units should be able to handle any new AVC cable content without trouble.
Media Center PCs are similarly OK, even CableCARD-enabled PCs should be fine. The tuner doesn’t change, only the decoder is different. So the existing clear QAM or CableCARD tuner should work just fine. Most newer PCs already have the capability to decode AVC/H.264 video, as it is a popular codec for online content and one of the codecs used for both Blu-ray Disc and HD DVD. Some PCs may need an upgrade to handle decoding HD H.264 content – if it can’t handle BD or HD DVD content, it probably won’t handle HD cable content either. It might simply mean a new video card, but older PCs may simply be out of luck. Still, odds are most Media Center PC users will have a reasonable path to support the new content.
However, those who have purchased Digital Cable Ready (DCR) TVs with CableCARD, or who use their TV’s clear QAM tuning, are probably out of luck. Very few HDTVs have MPEG-4 decoding built-in, and thus would be unable to tune channels using the new encoding. These users would be forced to switch to an external tuner – a cable STB, TiVo, etc – to utilize this new content. That’s the price of progress. It isn’t the first time these users have faced difficulties, they can’t tune SDV content either. And most HDTVs lack a USB port, and hence will not be able to utilize the forthcoming Tuning Resolver for SDV either.
Since this is coming, and you’ll probably have MPEG-4 channels on your cable system within the next two years, if you’re in the market for a 3rd party STB I’d make sure it can handle MPEG-4 content, or that it has some upgrade path to do so. (I wonder if the new Digeo Moxi boxes do? Something to ask at CES.) Right now you’re basically looking at TiVo or a decent Media Center PC.
This will leave just broadcast ATSC stuck at MPEG-2. I don’t expect that to change in the near future. With the cut-over to digital still a year away, the industry is just finally getting switched over to MPEG-2 ATSC. And nearly all of the ATSC hardware in the field, or being sold, today is MPEG-2 – with a few exceptions such as TiVo. Broadcast will probably be stuck with MPEG-2 for a long time to come.
