[ivtv-users] [ivtv-devel] NTSC & WSS (was: ivtv TODO list)

[Jay R. Ashworth]

----- "Hans Verkuil" <hverkuil at xs4all.nl> wrote:
> On Monday 18 January 2010 19:42:45 Devin Heitmueller wrote:
> > On Mon, Jan 18, 2010 at 1:35 PM, Hans Verkuil <hverkuil at xs4all.nl> wrote:
> > > - NTSC and WSS. I still do not know how NTSC determines whether the source is
> > >  4x3 or 16x9. PAL uses the WideScreen Signal (WSS). A similar feature exists
> > >  for NTSC, but it is unclear whether it is actually used by broadcasters.
> > >  Nobody seems to know.
> > 
> > The reality is that for NTSC there is no standard.  There is an NTSC
> > variant of WSS discussed in the WSS specification, as well as a way of
> > representing the info in EIA-608.  As far as I have been able to
> > gather though, neither have actually ever been used in production. If
> > someone wants to offer some evidence to the contrary, I would be happy
> > to add the support to tvtime and test it with some of my tuner boards
> > (and fix any bugs that in the driver I find).
> 
> Does that mean that you have to adjust your TV every time the format
> changes!?
> 
> Usually when I am in the US and watch TV in my hotel room the picture is
> always distorted. I really hope that is not normal behavior for NTSC and
> widescreen TVs.

The *actual* reality is that an NTSC signal has an inherent *signal* aspect
of 4:3.  If you're looking at it off a composite cable, or a cable/OTA tuner
you can force 4:3.  The *image* aspect may be different: wider aspects 
are generally accomplished by letterboxing, though some consumer camcorders
will record a 16:9 image as a 4:3 signal by doing an anamorphic squeeze of the
video image.

If it came in from a digital source, like a DTV tuner, things are murkier.

I *assume* there's an aspect flag, and I assume tuners will set it, but 
both of these issues should be orthogonal to IVTV, I think, cause we're
only concerned with composite NTSC and OTA RF NTSC-M, and you can safely
force 4:3 on both.

This is my technical understanding based on 20 years of making and editing 
the stuff; if anyone has a counterexample concerning broadcast or composite
transmission that I haven't already noted, bring citations.  :-)

Cheers,
-- jra

-- 
Jay R. Ashworth                   Baylink                      jra at baylink.com
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