When the ATSC standard was first proposed to the FCC, many people were aghast because it included so many formats. The infamous Table 3 in Annex A lists the SDTV and HDTV standards, frame rates and scanning formats (progressive and interlace) that would be permitted in the standard. (See Table 1.)
Table 3 would have been part of the FCC Report and Order, but the FCC never adopted it, preferring instead to leave decisions about formats to “market forces.” This could be viewed as a cop out, but the net effect was to allow the practical implementation of any format that consumer electronics decoders could cope with. So we have plenty of formats in use as a result.
One could argue that this presents no particular issue. Indeed, the FCC might say that it is only a problem for those who choose to use any particular format. However, in reality, it is an operational issue for many broadcasters, perhaps the majority.
The good news is that problems create niches to be filled, and plenty of manufacturers have leapt into the breach, beginning with the obvious up- and downconverters that were available when the DTV standard was first used in 1998. Today, conversions are done in baseband and even in compressed format (MPEG).
In a practical sense, the need arises in part because we are still one foot in an SDTV world while contemplating an HDTV future. Add the fact that a significant number of television plants are still analog NTSC, and the problem gets a tad more complex.
The real kicker is that even more formats are being promulgated. Some have interest from consumers, such as 1080p, which is attractive to high-end home theater buffs. Thus, studios might shoot in 1080p60 and make copies for all release formats from a pristine master, including 1080i and 720p for common HDTV release, and 480i for NTSC broadcast. That's fine, and you might say that the conversion problem is theirs, but this isn't true.
Today, it is common for one facility to feed more than one broadcast license. For the sake of argument, let's say that one is an ABC affiliate and one is CBS. Of course, they are the two most vocal proponents of 720p and 1080i. This wouldn't be a problem if you didn't have both HDTV and SDTV spots to insert in both DTV and analog outputs. If you only consider those formats, you have up-, down- and cross-conversion needs in one facility, plus whatever analog-to-digital conversions (or the reverse) are needed.
This leaves an obvious hole. Operations personnel must not only know the format of the intended output, but also the lineage of the content so they can pick the right converter box and route the feeds. In a positive development intended to alleviate some of the difficulty, boxes exist — in several price ranges — that do each of the needed conversions available. Even better converters can auto sense the input and automatically convert to the intended output format. Some will provide both HDTV and SDTV outputs at the same time, taking much of the burden off of a busy operations staff.
But before you can pick the necessary converter, you should carefully consider the requirements that need to be satisfied and the expected performance from the device. It is not appropriate to pick converters by price alone (either by buying cheap or unnecessarily spending money on an all-dancing bear). There are silicon scalar solutions available that can be used to build complete converters that convert both directions for less than $5000. They do a good job and are perfectly credible for many applications. They are generally limited by the quality of the filtering done and feature set available. Some have been built into standalone boxes, which might be mounted on a panel, such as a monitoring converter. They offer somewhat limited operator controls, though via serial interfaces, full control is possible.
Choosing such a device for primary use may be appropriate in smaller markets where price is a primary driver in the decision. However, in a large station or major production center, a more complete and full-featured solution is usually needed. In addition, these “Cadillac” solutions may offer superior filtering. Indeed, some manufacturers tout filtering as a defining difference in their high-end products. For some applications, this can be true.
Other features to consider
Consider the operator interface as well. Some products are intended for remote mounting and computer control. Others have full controls on the front panel and/or offer remote control panels designed for the device. In a master control room environment, it may not be appropriate to have an additional computer screen for controlling the operation of conversion equipment. But if that control can be combined in a system that offers SNMP monitoring of servers and other terminal equipment, it may be justified.
Aspect ratio conversion is normally part of the feature set of these converters. With the rise in the number of changes between 4:3 and 16:9 programs and interstitials, there will come a time in the not too distant future when automatic switching back and forth will be desirable (and likely carried in the information passed by traffic to the automation log).
Look for a system that can accept a command to change aspect ratio as needed. Presets that accommodate the look you normally prefer are a great feature. For instance, today you might want to letterbox a 16:9 program on the NTSC channel, but run commercials full-screen, with the reverse on NTSC. In the future, you may want to convert all content to 16:9 when NTSC shutdown happens (or whenever your audience has a high percentage of wide-screen displays).
Lastly, audio concerns should be taken into account. Video processing engines, such as these complex scaling engines, create latency in the picture content. When implemented, matching audio delays must be planned. Many conversion solutions offer this internally.
If you are using embedded audio, be sure the device you pick can accommodate it. Check with the manufacturer to ensure multichannel audio on AES (Dolby AC3 and Dolby E) will pass through unmodified. If you have discrete levels of audio to handle multichannel sound, be sure all channels will pass through the solution. It's also important to ask the manufacturer if both SD and HD inputs are handled the same way.
John Luff is the senior vice president of business development for AZCAR.
Send questions and comments to:email@example.com