[opendtv] Why can't POSTAGE STAMPS be Eliminated???
- From: John Willkie <johnwillkie@xxxxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Fri, 19 May 2006 17:35:15 +0000 (GMT+00:00)
The quick answer is that there is no requirement per se that letterboxed
programs must be transmitted in such a fashion.
Most of the items in respose so far have been about receiver issues, but last
time I checked, receivers didn't actually transmit.
Mark mentioned William C. Miller's paper at the most recent NAB. There is
active work at SMPTE on this matter, including two ballots on metadata that
will be used to dynamically change the bar data and active format description
elements that are part of ATSC A/53 and ISO/IEC 13818 (MPEG-2). As a member of
SMPTE's WG 22-10, which is handling this matter, I've probably already said too
much.
As has been alluded to on this list in recent months, there can be a disconnect
between the video frame that is used (say 720x1280) and the active video area
(there could conceivably only be 480x640 video within that frame.) If the video
is smaller than the "window", sometimes the video might be centered within the
window, or at other locations.
If the video source is letterboxed, the problems are only magnified. Spots and
programs might have different settings, making the issues quite dynamic.
Active format description, when supported upstream, will permit the encoder to
describe the actual live video portion of the window. Bar data permits
describing what parts of the window are unused. By transmitting these elements
as broadcast metadata, a properly implemented receiver wll be able to use both
to scale the image accordingly so that the active video area keeps it's aspect
ratio (if that is the user's preference) but is scaled as large as the receiver
will permit.
Craig is right about the non-compliant chip sets, but that's now a very old
issue that has been overtaken by events and improvements. Those older chip
sets won't process AFD or bar data. If I'm not mistaken, the NAB/MSTV RFP
required AFD/bar data compliance in their $50 stb.
Showing video in one format on the screen and another at the S-video output
sounds non-trivial to me. Which means that it will take longer to solve.
John Willkie
___________________
Richard Hollandsworth wrote:
Why must Letterboxed programs (e.g. Widescreen 720x480 DVDs) be transmitted as
a 360x480 "Postage Stamp" within the SD 640x480 4:3 box?
Why can't they be transmitted in either 720x480 (currently in SCTE specs) or as
"SD-Lite" 704x480 (currently in both SCTE and ATSC specs)?
Surely the Encoding equipment is capable of handling this resolution
setting.....
An HD-STB/DVR (whether built to ATSC or SCTE specs) should be capable of
accepting this format without modification, filling up the screen on a 16:9
HDTV.....and "shrink-to-fit" for Video/S-Video output, just as they already do
for HD.
Shouldn't a cable SD-STB also be capable of accepting widescreen
formats---after all it's one of the 480 formats in the SCTE specs???
If not, wouldn't it be a viable software-only upgrade???
=============================================
ATSC Candidate Standard CS-TSG-674 proposes revising Table A3 in ATSC A/53
Annex A to (finally) include the 720x480 widescreen SD resolution, indicating
that it has been in use for several years with any reported complaints.
So there may not even be a need to down-rez ATSC to "SD-Lite" 704x480.
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