AFD and Me

So I get back from vacation, after I had just put in a new exciter two days before I left. I checked on it today and all is well, it’s making power and I have had no complaints from AT&T U-verse about our DTV signal being 16 VSB instead of 8 VSB. So far so good.

Now I hear from the boss that right after I put in the new exciter he was seeing some changes in the picture, like it had blown up, gotten bigger and was cutting off logos and crawls. He also got complaints from DirectTV and a couple of viewers. Even my buddy who is running his own channel our our station said he noticed some change in the picture but thought it was just him.

So I went up and took a look, I checked the encoders and their format, it’s 704 H just like it’s always been, I even switched between the old exciter and the new ATSC 8000 to look for any change in the picture size, but it was the same. Now one reason I checked was that the new exciter gets ASI and the original one gets SMPTE 310 from the Thomson Turquoise converter. So it all looks the same to me, I see no problems.

Then I get a call from the boss who says that DirectTV has informed him that we are transmitting an AFD signal or Active Format Description signal. This is a special signal thats imbedded within the video signal in VANC, or Vertical Ancillary Data Space. What we used to call Vertical Blanking, but is now called VANC in SDI. What AFD does is tell any conversion equipment how to format the video for display, like a wide screen HD video may want the edges cut off to make it fit in a 4:3 format when viewed on SD monitors. Or it may tell the converter to add top an bottom bars to in a letterbox format. Either way the AFD lets the broadcaster choose how their video gets formatted to fit other screen sizes or formats.

The DirectTV guy says we’re putting out a Code 8 AFD and we should be putting out a Code 9. Well I’ve never had to deal with AFD before so I looked it up to see what was what.

Code 0 – is reserved for ATSC
Code 1 – is also reserved
Code 2 – ETSI: 16:9 (top aligned) not recommended
Code 3 – ETSI: 14:9 (top aligned) not recommended
Codes 5 – 7 – are reserved
Code 8 – is Full Frame image, same as the frame (what goes in goes out, 4:3 or 16:9)
Code 9 – is 4:3 Full Frame in 4:3 frame or Pillarbox for 16:9
Code 10 – 16:9 image Letter box in 4:3 frame or Full Frame in 16:9
Code 11 – 14:9 Pillargox/Letterbox image
Code 12 – unused
Code 13 – 4:3 with Shoot and Protect 14:9 center
Code 14 – 16:9 with Shoot and Protect 14:9 center
Code 15 – 16:9 with Shoot and Protect 4:3 center

So DirectTV says we are putting out a Full Frame image and telling their equipment to put out the same, whats so hard about that?
What they want us to output is 4:3 Full Frame in and 4:3 out, whats the different? We only broadcast SD, it’s all 4:3.

As you can see AFD is needed for HD conversion to SD, but we are only SD and where is this Code 8 DirectTV is saying we are putting out?


Could it be that some of our programs have AFD built in and it’s passing through but others do not and the DirectTV equipment gets confused when the switch occurs?



I wrote to AT&T U-verse and asked them to look at my signal to see what if anything I was putting out concerning AFD and they told me that there was nothing there, just as I suspected. The next time we talked to Direct TV they said they would have to get a technician that knew about this stuff and  they would get back to us. Next we heard from Dish and they just asked us what format we wanted to be set to and I told them 4 by 3 (we are SD only), they said fine and they would talk to Direct TV and get them to change their receivers to output the proper AFD code. So hopefully everything is good now.

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