[opendtv] Re: Popular screen aspect ratios

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Sat, 8 Jan 2011 09:02:59 -0500

At 11:18 AM -0800 1/7/11, dan.grimes@xxxxxxxx wrote:
While this should be true, it doesn't solve a myriad of faults, even if the source device and the TV are interconnected through an HDMI cable:
Please note: I did not say you would not need to adjust the form of aspect ratio accommodation for the display. I was simply saying that you do not use the aspect ratio accommodation features of the external box/decoder.
1. The broadcasters are not using AFD properly so even if the TV and STB (or other device) is processing properly, the STB might not know that it is non-square pixel.
For SD, you may need to use any number of accommodation schemes. If the source is 4:3 you can watch pillarboxed, zoomed to fill the screen, or a combination with distortion. For 16:9 you may need to expand the source to fill the screen width, or expand further if the source is letterboxed into 16:9. These accommodation modes are available on most DTV displays.
2. CE devices don't always know how to properly deal with the encoded media and fit it properly into t he 16:9 space.
There can be encoding and metadata errors, and some boxes may just be nonconformant. But you can typically use one of the displays accommodation modes to correct the presentation. It is noteworthy that on a computer you can simply change the size and aspect ratio of the window and make these kinds of adjustments - I have not seen this on any DTV, but clicking and dragging is difficult with a numeric remote... ;-)
3. Once the single coming from a source (STB, DVD, BD, gaming console, etc.) is sending a 16:9 image to the TV, the TV doesn't know what the media is. This could be the fault of the TV or it could be the fault of the source. That is, the TV might not use the aspect ratio or display information provided on the HDMI signal or the source device might not be sending the information the the HDMI signal. 


See answer to #1
4. TVs (or source devices, for that matter) do not have a convenient way to manually override any faults. That is if the material is 4:3 and being displayed stretched in 16:9, there is no way to tell the TV that even though it is receiving a 16:9 signal, it really is suppose to pillar box it.
Odd. I've not had this issue with our displays. But different manufacturers offer different ways to accommodate multiple formats.
5. AFD only deals with 16:9 or 4:3. As we all know, there are a tremendous number of aspect ratios to accommodate. 

But who is using them in the "TV space?"
We have already established that most computers deal with this stuff automatically using the metadata in the encoded source. This allows the computer to deal with ANY format automatically.
In the "TV Space," however, everything is forced into a 4:3 or 16:9 container. But this typically works OK for sources that are wider than 16:9 - i.e. you drop lines and letterbox. There are some challenges, like 1.66:1 movies, and legacy 4:3 movies as Cliff has noted. But the issue here is stuffing it into the container properly and creating the correct metadata.
I could go on. If anyone has tricks or settings that can overcome any of these issues, I'd love to hear them.
I'd like to hear more about this kind of problem as well. It seems that the TV guys have so compounded the problems that it leads to bad outcomes. If we rely on proper identification of the encoded samples ,and the ability of a display processor to scale independently in the H and V axis it is relatively trivial to get this right all the time. 

Sometimes limiting choices leads to MORE COMPLEXITY.

Regards
Craig


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