[opendtv] Re: Popular screen aspect ratios

  • From: Craig Birkmaier <craig@xxxxxxxxx>
  • To: opendtv@xxxxxxxxxxxxx
  • Date: Mon, 10 Jan 2011 09:13:49 -0500

At 6:29 PM -0600 1/9/11, Manfredi, Albert E wrote:
You're describing what you think COULD be the case, or maybe what you thought was the case, but not what is the case. It's important to clarify this point. It would also have helped if the FCC knew this, back when.
No, I am describing what IS the case. The FCC knew this before they saw the ATSC standard, because the MPEG-1 standard presaged these concepts, and the MPEG-2 spec was well developed before they ever saw the final Grand Alliance system. If the FCC erred, and they did, it was in the manner in which they attempted to modify the ATSC standard - i.e. removing the restrictions on the MPEG-2 standard imposed by Table 3.
Instead, the FCC SHOULD HAVE simply said that the ATSC standard should fully adopt the MPEG-2 profiles for SDTV (MP@ML) and HDTV (MP@HL), and that all decoders should be fully conformant.
What we learned here in the past weeks is that decoders do need to know about the display, whether they are connected via digital or analog interfaces. In the digital case, they get the information automatically, is all.
Only for legacy 4:3 analog display, as these devices have no means by which to accommodate multiple formats. For new DTVs the critical issue is making the metadata available to the display processor, which is trivially easy for TVs with an integrated ATSC receiver. 




 All the rest of this is the result of piss poor system design and an
 unnecessary effort to restrict the capabilities of the TV system.
This is not limited to TV. PCs have the same problems. When connected via RGB to some oddball display, you have to enter the customized settings into the video card, via a CD-ROM.
This argument continues to be irrelevant. How a display connects to a PC is TOTALLY decoupled from how a PC processes MPEG-2 bit streams and displays them.
My only unresolved puzzle in all of this is, how did my new PC know that the monitor it was feeding was an LG? Not that the PC or TV had set themselves correcly or anything, but what told the PC that the TV was of a particular brand? Must be some of those extra pins in the RGB interface?
There have been monitor identification signal pins in the VGA specification for about two decades (pins 11,12, and 15). Initially these pins were either open or grounded - the resulting three bit codes could identify 8 diferrent VGA resolutions. Later pins 12 and 15 were allowed to carry what is called DCC data; pin 12 carries the data while pin 15 is the clocking signal. Any display that supports DCC data communication can identify itself to a video card that also supports DCC data. 

Here is a more extensive explanation:

http://www.epanorama.net/documents/pc/monitors.html
In addition to video signal, the VGA connector has some monitor identification pins (pins 11, 12 and 15) that allow PC video cards to determine what type of monitor is connected to the graphics card. The originaal plan used to such that the monitors grounded some of those pins to tell that the monitor is there and what type of monitor is there. Modern plug&play monitor systems have changed their use in such way that pins 11 and 15 are used for DCC data communications between computer and monitor (pin 12 = DDC DATA, pin 15 = DCC Clock). The extra control signals are generally carried through separate wires (all inside one cable main shield). 

Regards
Craig


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