I’ve been expecting this to happen at some point, but it slipped by without my noticing. The provision for future extension had always been in ATSC, but back on July 29th, the Advanced Television Systems Committee, stewards of the formation of standards which constitute what we know as ATSC, has published a new spec, A/72, which covers the use of AVC in ATSC. (AVC (Advanced Video Coding) is aka MPEG-4 Part 10 also aka H.264.) It was pretty much inevitable as satellite has already moved to H.264, and digital cable is just starting the transition with H.264 being used for distribution and just starting to show up in the last mile. Since H.264 is far more efficient than MPEG-2 it provides for a much more efficient use of the available bandwidth.
However, most ATSC tuners on the market today have no H.264 support. And that includes the digital converter boxes available now for users preparing for the digital transition next February. That means we’re unlikely to see H.264 used for broadcast ATSC in the US for many years, if ever. It would make the content unavailable to the installed base of receivers. H.264 is more likely to be used in other countries still considering ATSC as a possible standard (though DVB-T is really dominating the global markets, so I don’t really expect a lot of ATSC usage).
In the US ATSC with H.264 will most likely see usage in new services such as ATSC-M/H (mobile/handheld) and ATSC-NRT, which will utilize new receiver hardware anyway. ATSC-M/H is fairly obvious, the concept would have an ATSC tuner incorporated into phones, etc. This is like DVB-H deployed in some other countries. The broadcasts would be specially formatted for handhelds and would use dedicated sub-channels, so they don’t need to be compatible with existing receivers. ATSC-NRT is for Non-Real-Time content delivery. Basically a ‘trickle-cast’ of content which can be carried on a sub-channel for use later. This is similar to how DirecTV or DISH Network will deliver ‘OnDemand’ content to their DVRs ahead of time. New devices with ATSC-NRT support could receive content in advance for OnDemand movies, special content, etc. It could be used to download interactive content for ACAP, advanced advertising (similar to TiVo’s capabilities today), or other data content. Since these would be new devices anyway they could use H.264 to take better advantage of the available bandwidth.
It is possible that we might see H.264 used for secondary sub-channels for additional broadcast content. That way customers with existing content would not lose anything, they just wouldn’t gain the new stuff. This is similar to satellite companies adding new content using H.264, leaving customers with existing MPEG-2 receivers to keep existing content only. Or cable companies using SDV for new content, so existing customers only have their pre-existing channels. The H.264 subchannels could be used for things like alternate angles on sporting events, re-airing popular shows (air the new episode on NBC1 on Monday, re-air it on H.264 NBC2 on Wednesday – get more total viewers), or even special content – movie on main channel, movie with commentary on subchannel. Of course it is a chicken-and-egg issue – channels won’t do this until receivers handle H.264, and the only H.264-enabled ATSC receiver I can think of off hand is TiVo. Wait, and the newer satellite DVRs that have ATSC tuners as well.
I don’t expect to see it used on primary channels for a long, long time, if ever. Not until nearly all receivers in use in the field support H.264. No one wants another major transition any time soon, we haven’t even completed the first one yet. And ATSC is 25 years old already. (Yes, work started in 1983, believe it or not.)
Of course, the committee is working on ATSC 2.0: “ATSC-2.0 will define a complete suite of ‘Next Generation’ services for the conventional fixed DTV receiver viewing environment.” But I suspect ATSC 2.0 will be a super-set of ‘ATSC 1.0′, adding interactivity, etc, to the content through ACAP (think OCAP for ATSC).