The list of unfinished business includes program insertion and splicing; emergency messages on cable systems; copy protection; data broadcasting and multimedia services; forced tuning of TV tuners; audience rating data; and other items. Digital TV will continue to evolve. Here are some details.Program insertion and splicing
How does a broadcaster or cable operator insert a commercial? The issue here is that compressed digital signals usually only refresh the portions of the picture that change. Only occasionally is a complete picture (called an "I frame") transmitted. So if you cut to a commercial, you want the cut to be synchronized with the transmission of a complete picture. Otherwise, you'll wind up with an unappetizing display of hash on the picture tube. Both SMPTE (for the broadcasters) and SCTE (for cable) are working on procedures that should be followed, and equipment developers are working on products that insert and identify synchronization points in the program stream. But they aren't finished. Meanwhile, insertion of commercials and switching between program streams on DTV may look less polished than on analog TV.
What about emergency messages? When a broadcaster runs an emergency message, such as a crawl at the bottom of the screen announcing a tornado warning, he may have to take the digital video that comes in from the network, convert it to analog, add the crawl, reconvert it back to digital, and then transmit it as a digital signal. For a cable operator, the equipment requirements make it too expensive to do that for every channel. One alternative is to place the emergency message on a separate channel and force tune every set-top box to that channel. Or maybe there's a better way to do it. Forced tuning of the set-top box is easy, because the commands come down the out-of-band data channel. But cable-ready TVs may have a more difficult time. I don't know how this will get resolved, or when.
Don't bother trying to record a digital TV transmission on a digital VCR. There may not be any digital VCRs, at least until the copy protection controversy is settled. Hollywood studios have approved one particular approach, but it is viewed by some as too expensive, partly because of the royalties that will have to be paid to the inventors. Once the technical approaches are developed, there will be legislation making it illegal to circumvent the copy protection systems that are built into digital TVs and VCRs. But I can't tell you when this will be resolved.Data broadcasting and multimedia services
Standards are being developed, but unlike the Grand Alliance digital video compression and transmission standards, the data broadcasting standards are nowhere near done. While some extol the convergence of computers and broadcasting, I find this whole area confusing. I wonder what applications will find consumer acceptance. Do I want to watch TV broadcasts on my computer? Surf the Internet on my TV? Send home movies embedded in e-mail? Display batting averages on my TV set while watching a baseball game? All of these are possible data broadcasting or multimedia applications, but they all require a different set of hardware capabilities. Or at least I think they do. But I'm confused. What does "convergence" really mean?
Meanwhile, there are continuing requests to modify various aspects of the digital TV standards, because new ideas keep popping up, like the following:
- Forced tuning. A newspaper publisher can force you to accept a zoned local news section. Why can't a broadcaster force you to watch the zoned local news for your part of the city? By typing in your zip code the first time you turn on your TV set, something like that is possible. But it requires a change in the digital TV standard. Such a change has been requested, by a broadcaster who just also happens to be a newspaper publisher.
- Audience ratings. It's possible to detect which TV channel you're tuned to, regardless of analog or digital TV, because there is a slight amount of signal leakage from the local oscillator of the TV tuner. So a ratings service could install a box in your home, and you wouldn't have to fill in those diaries. But with several standard definition TV programs riding down the same 6 MHz video channel, just knowing the channel number isn't enough. A simple change to the DTV standard, which has been requested by some broadcasters, would allow a box to be hooked to the TV, where the box would send a message to the TV asking which subchannel you are actually watching.
The digital TV standards will continue to evolve as marketing people uncover or create new demands, and technologists develop new capabilities. Hang on for the ride!