AFD at NAB:
Watch video from the floor of the 2008 NAB Show, where NBC Universal promoted its AFD technology.
While HDTV programming continues to take off and consumers keep buying widescreen HDTV sets, one of the realities of the digital TV transition is that broadcasters will still be delivering pictures to analog, 4:3 sets for some time after they cease analog broadcasts on Feb. 17, 2009.
Cable and satellite operators will downconvert the HDTV signals to provide standard-definition pictures to subscribers with analog sets and/or standard-def set-tops. Over-the-air viewers will use digital-to-analog converters to watch the DTV programming on old analog sets.
And low-powered TV translators, which are used by broadcasters to fill in coverage gaps in rural areas, will also downconvert the HDTV signals to analog before retransmitting them, until they eventually migrate to all-digital operation.
Some networks, such as CBS, are producing all of their HDTV content in “center-cut safe” mode to prevent problems when they are downconverted for display on 4:3 sets. But NBC Universal and other programmers would like more flexibility in how their content is displayed, and have been promoting another new set of initials: AFD, which stands for Active Format Description technology.
AFD has been standardized by television engineer groups and the Consumer Electronics Association as a method of describing the aspect ratio and picture characteristics of video signals. It inserts descriptive data in an HDTV feed that allows broadcasters to control how downconversion equipment, such as a professional receiver at a cable headend or a consumer digital-to-analog converter, formats widescreen 16:9 pictures for display on 4:3 sets.
The goal of AFD is to give program producers and advertisers a choice of how their content is displayed on a 4:3 set and prevent viewers from seeing postage-stamp-sized pictures or having graphics designed for widescreen pictures cut off during 4:3 display.
For example, NBC has been using AFD internally in its production chain since 2005 to direct how its HDTV programming is reformatted for standard-definition delivery. News and sports programming is reformatted via AFD to be displayed in full-screen, 4:3 mode, while primetime entertainment programming is delivered in letter-boxed 16:9 to analog sets.
“The entertainment content does lend itself more to the wide-aspect-ratio production, so what we've done is to deliver an HD version and a letterboxed SD version,” explains Clarence Hau, director of systems engineering for NBC Universal and its DTV transition project leader.
But for AFD to work across the TV universe, NBC needs cooperation from cable and satellite operators, broadcast technology vendors and consumer electronics manufacturers.
To that end, NBC teamed last spring with station groups Hearst-Argyle and Tribune to form the “AFD Ready Initiative,” which was intended to raise awareness of AFD among manufacturers and multichannel operators. Cox Broadcasting, Fox Television and PBS have since joined the group, and over 20 professional manufacturers have agreed to support AFD in their products. LG Electronics and Dish Network have also included AFD capability in their digital-to-analog converter boxes.
Now NBC Universal has successfully tested AFD with both multichannel operators and low-power TV translators using live broadcast signals from affiliate KOB in Albuquerque, N.M.
NBC conducted the tests late last month with Hubbard Broadcasting-owned KOB, which was selected in part because it retransmits its programming through a network of translators that reach across New Mexico and into parts of Colorado. The tests also drew the participation of multichannel operators DirecTV, Dish Network and Comcast.
For the tests, NBC and KOB used a Miranda MMX1801 card to insert AFD information into the station's HD signal before it was compressed for local broadcast using a Tandberg E5780 ATSC encoder. The HD over-the-air signal was then received by an antenna at the joint DirecTV/Dish collection site in Albuquerque, where it was demodulated and downconverted under AFD control using a Sencore MRD3187 professional ATSC receiver. The signals were then passed on to DirecTV and Dish for standard-def distribution.
KOB also placed R.L. Drake DAD860 ATSC receiver/downconverters at five translator sites, where the station's HDTV signal was downconverted and demodulated to analog under AFD control and then rebroadcast as analog NTSC signals. Sean Anker, director of engineering and production for KOB, expects that process will be in place for some time after KOB's high-powered analog signal is turned off in February.
“We'll be transitioning the whole network to digital over time, but primarily we'll be delivering a standard-definition analog signal,” says Anker. “That's why the test is so important to us, as we're hitting so many small towns with low-power analog signals.”
The AFD test was also important to DirecTV, which is in the process of switching many local collection facilities from analog to digital receive equipment.
“Absent AFD, you have to decide to permanently lock in the receiver to downconvert to either a 16:9 letterbox or 4:3 center-cut,” says Hanno Basse, DirecTV VP of broadcast system engineering. “And not all programming lends itself to being boxed in permanently. That's why we agreed to test the performance of AFD technology, and it works pretty well.”
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