Path: utzoo!utgpu!watserv1!watmath!att!hriso!attdso!ssc!markz
From: markz@ssc.UUCP (Mark Zenier)
Newsgroups: sci.electronics
Subject: Re: Television VBI Data transmissions
Message-ID: <378@ssc.UUCP>
Date: 13 Jan 90 00:36:07 GMT
References: <599@limbic.UUCP>
Organization: SSC, Inc., Seattle, WA
Lines: 32

In article <599@limbic.UUCP>, gil@limbic.UUCP (Gil Kloepfer Jr.) writes:
> 
> 	1.  Are there any FCC regulations or industry standards
> 	    which govern the VBI, and how signals are to be
> 	    superimposed here?

The FCC says where.  The what is up to the originator.  There are a couple
of systems used in the US.  NABTS is defined in an EIA standard.  The
version I have is called an interim standard (IS-14).  It may be real
by now.  World Teletext is derived from the UK system.

> 
> 	2.  Specifically, how is closed captioning transmitted?  Is
> 	    it data, or a slow-scan representation of pixels to be
> 	    overlayed on the TV picture?

ASCII.

> 
> 	3.  What is the best way to get at the information on the VBI?
> 	    Specifically, what is the best way to detect the start
> 	    and end of the "dead" portion where information would be
> 	    transmitted?

Most signals have a distinctive header that exists in a fixed relationship
to the horizontal sync.  Just look at every line to see if it fits.

A quick browse thru "Television Engineering" by Benson will give you a lot.
For the WTS system, try the Signetics Linear Data Book volume for Video
products.

markz@ssc.uucp