KXAN (NBC in Austin) Changes format of upconverted video - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 2 Old 04-18-2002, 07:40 AM - Thread Starter
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I have been a bit frustrated with the inability to zoom digital 4:3 material on KXAN -- specifically, ER is my fiance's favorite show. Because they sent a 16:9 signal, my TV won't allow it to scale. We end up watching the analog broadcast on 36 for ER because we can zoom it.

I sent a letter to KXAN engineering, here is the letter I sent and the response. I'll explain what actually resulted after the letters.

My letter to KXAN:


-----Original Message-----
From: Joseph Shovlin [mailto:shovlin@extremedevices.com]
Sent: Tuesday, April 16, 2002 3:38 PM
To: engineering@kxan.com
Subject: digital television broadcast on channel 36-1


This is a fairly technical question and request dealing with KXAN-DT.

I have beeen VERY happy with your broadcast on 21-1 (or, remapped, 36-1); when available, HDTV is breathtaking. I wish NBC provided more high definition programming for you to broadcast! The Olympics were spectacular, the recent Mavs/Spurs game was awesome, and I find myself watching shows like Crossing Jordan and the Tonight Show for the picture itself. There are rumors online that prime time in the fall will be high definition -- I can't wait!

I have an small issue with the regular digital broadcast on 21-1; the problem does not appear to occur on 21-2 and 21-3.

I have an RCA directview F38310 high definition television.

When watching analog 4:3 material, or the 4:3 material on 21-2 and 21-3, my set adds "gray bars" to the right and left edges of the screen. The F38310 allows you stretch mode and a "full" zoom mode (which is perfect for letterboxed shows like ER). I can scale the digital material on 21-2 and 21-3, and the analog video on 36.

The trouble comes when I watch 21-1. First, there are no "gray bars" on the side. Second, I can't scale the video. The television set thinks it is receiving 16:9 video, and so it leaves off the black bars, and locks the zoom mode. The way folks have explained it to me on-line (I regularly visit the AVS Forum, www.avsforum.com), is that your signal is formatted at 16:9 even though the actual transmission is 4:3.

The dangers of aging the center phospor faster than the side-wings (due to lack of gray bars) aside, my fiance's favorite show is the letterboxed ER. Unfortunately, because we can't zoom the screen for 21-1, we are forced to watch the zoomable analog broadcast on channel 36!

Is there any way you can send non-high definition video like ER in a 4:3 format so that we can scale it?

If I have confused you by my description, please don't hesitate to follow up via email, during the day at the number in the signature below, or in the evening at home, 291-9460.


This was Mark Dunham's response:


Mr Shovlin,

You have prompted me to make changes today that I have been mulling over for the past few months. We are still transmitting our upconverted signal in a 16:9 aspect ratio but it is now in full-screen mode.

You have collected accurate information and your quandary is very clear to me. Let me give you a little more info and explain why we format the channels the way we do. KXAN-DT is comprised of 3 program streams - one HD and two SD (Standard Definition). Each stream has an individual piece of hardware associated with it (an Encoder) that specifies the aspect ratio. The SD encoders accept an analog signal in and we have configured those to maintain the 4:3 aspect ratio - this allows the flexibility on the receive end that you describe to zoom or stretch the picture to fill the screen (As an aside - of the 19Mbs available on an HD studio stream, each SD channel is allocated 1.75 Mbs and the HD channel is 15Mbs. The remainder is audio and PSIP data necessary for your tuner to decode the signal). The HD stream has an additional piece of hardware - an Upconverter. This piece of gear takes our analog KXAN signal and converts it to a 1080i HD stream that feeds the HD encoder. The 3 encoders are combined in a multiplexer that feeds the transmitter.

Your request is that we transmit the upconverted signal in 4:3 format. I can change the aspect ratio in the upconverter and/or the encoder to 4:3 but the HD encoder has the last word. Our HD encoder is configured for 16:9 so that the NBC pass through programming will display in the correct format without human intervention. To change an encoder setting requires an engineer to reconfigure software and then restart the application services associated with the encoder. This takes the channel off air for a few moments - if everything is done right. We are a relatively early adopter of HD (we went on the air in 2000) and our equipment is not sophisticated enough to sense the incoming signal and format the output accordingly.

In a nutshell - we format the way we do because the alternative is labor (and overtime) intensive. Today I adjusted the upconverter to fill the 16:9 screen. I zoomed the picture ("zoom" IS an adjustment on my $60,000 upconverter also) to fill the horizontal screen. This of course caused loss of picture information on the top and bottom of the screen. I then reduced the vertical size until I can just see lower third graphics. This caused a bit of distortion in the aspect ratio but I believe it is a happy medium. Not very scientific I admit, but the adjustments I made are a compromise between "stretched' and 'zoomed'.

Let me know what you think - we do very much value the feedback from the few HD aficionados out there. Right now we are a fairly small community and I enjoy discussing the evolution of the new medium with the early adopters.

Mark Dunham
Chief Engineer

This is the change he made fore the upconverted non-16:9 programming:

Rather than send it in 4:3, zoomed it for the sides to fit the 16:9 window, and then squished it vertically a small amount to make the aspect ratio distortion less. It is inbetween a standard stretch to fill the 16:9 window without changing the vertical size (as in the "full" mode on a 16:9 TV set), and a zoom to expand a letterboxed video to fill the screen ("fill" mode on a 16:9 set).

I'm going to need to watch it for a day or two before I decide wether I like it or not.

What do y'all think of the results?

Distortions are most apparent when there are commercials with graphics on them -- the letters just don't look right.



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post #2 of 2 Old 04-18-2002, 10:49 AM
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That is some great info. Thumbs up. Unfortunately, I no longer have my HD decoder... couldn't justify the cost for the amount of programming on KXAN. However, when we get at least CBS here, I'm all over it again... or if NBC goes primetime HD.

Hopefully some of the other active austinites who have TV's similar to yours will chime in... Thanks for the info!
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