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From: rwhite@nu3b2.UUCP (Robert C. White Jr.)
Newsgroups: comp.graphics
Subject: Re: Why not streaming video recorders?
Message-ID: <794@nu3b2.UUCP>
Date: Fri, 10-Jul-87 21:29:39 EDT
Article-I.D.: nu3b2.794
Posted: Fri Jul 10 21:29:39 1987
Date-Received: Sun, 12-Jul-87 14:18:45 EDT
References: <17110@glacier.STANFORD.EDU> <2328@dciem.UUCP>
Organization: National University, San Diego
Lines: 41
Summary: How it works.


Since the veido recording head spins on its axis and it's axis is
on a bias [slanted with respect to] to the direction of tape travel
a veido tape is "always in motion" even if the tape is not traveling.
Each image is a diagonal stripe on the tape so seccuessive frames are
dropped in anad apear as:
frame #:   1 2 3 4 5 6 7 8
         ---------------------
	   \ \ \ \ \ \ \ \ \ \
	  \ \ \ \ \ \ \ \ \ \
...
           \ \ \ \ \ \ \ \ \ \
	  ---------------------
on a segment of tape.  The problem is that the jog [forward|backward] until
sync is dificult to maintain/produce.  Even good consumer level VCR's 
have some problem keeping an acceptable "still frame" [stop the tape and
keep the head engaged and spining]  Multiple "heads" on a single "head
drum" are used to catch the slack and skew.

	Extreemly good veido tape editors have a "multi head" drum and
two extra little arms which travel the tape in increments of millimeters.
The controll circuts which preform this act are extensive and expensive.
Beacuse a computer would be more upset than a human eye about the loss of
bits most vedio/data medimum write seccuessive frames of identical data.
A system could easily be designed to "still frame" data but TWO sets of
"travel arms" would be required 1) alignment on amilimeter basis, and a
data-frame-by-frame set to account for/remove startup skew and tracking.
Such a device is easily possible, but quite expensive without quantity
purchases [thousands].  It can't really be added on to an existing VCR.

Further Details Available.  [I know a lot about veido from my high school
minor]


Robert.

Disclaimer:  My mind is so fragmented by random excursions into a
	wilderness of abstractions and incipient ideas that the
	practical purposes of the moment are often submerged in
	my consciousness and I don't know what I'm doing.
		[my employers certainly have no idea]