Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!rutgers!mcnc!thorin!oscar!tell
From: tell@oscar.cs.unc.edu (Stephen Tell)
Newsgroups: sci.electronics
Subject: Re: automatic commercial deletion
Keywords: commercials, compressors, VCRs, film editting
Message-ID: <9573@thorin.cs.unc.edu>
Date: 20 Sep 89 05:03:16 GMT
References: <6428@ingr.com> <11213@fluke.COM>
Sender: news@thorin.cs.unc.edu
Reply-To: tell@oscar.cs.unc.edu (Stephen Tell)
Distribution: usa
Organization: University Of North Carolina, Chapel Hill
Lines: 57

In article <11213@fluke.COM> inc@tc.fluke.COM (Gary Benson) writes:
>I once toured the Public Broadcasting studios in Madison, WI. I seem to
>recall that there is in fact a "blip" sent that studio equipment can detect,
>(the human eye can, too, if you know where it is and when it will
>be coming). It is about as fast as a half an eyeblink, and I believe it is
>simply a small white circle (or target) in the lower right corner of the
>screen. In my memory of all this, the blip was sent some precise interval
>(one second or 5 seconds) before the changeover, and it occurred in the
>program before the station break, and in the commercial prior to returning
>to the program.
.... stuff deleted ...
>GaryBenson_-inc@tc.fluke.COM-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_

This sounds suspiciously like the timing dots used on film to help
the projectionist switch over between reels.  I suppose it could
be generated electronicly and used for commercial insertion too,
but it seems a bit hard to detect, especialy if the picture is nearly
white in the area of the blip...

Anyway, about how the film thing works:  35mm film only fits about 20
minutes to a reel of ~15 inches, so every movie you watch in a theater
has several changeovers.

Before the movie opens at your theater,
someone watches the film and notes what scenes the dots occur in.
When the changeover comes around, the projectionist has the next reel
mounted on the other projector, and queued to a special 'start frame'
by hand.  He/She watches for the afforementioned scene, and when they see
the dot(s), usually in the upper right hand corner, they start the
second projector rolling.   Exactly five seconds later, more dots appear,
and the first reel is over.  The projectionist opens the shutter on
the second projector, and simultaneously cuts the sound over, usually
with a foot pedal.  The first reel's lead-out is black for a while, to
give them time to reach over and close the shutter before shutting down
the projector and removing the reel to make way for the next one.

I may have some of the details wrong, I never actually ran one of these,
but have hung out in the booth while this was going on.  I think some
theaters have some way of automating this, I think by metal clips attached to
the film at the point of the changeover.  
Before I was told this, I never saw the dots, but now I always do.  The
actual changeover comes at a cut between scenes, so it usualy isn't too
noticable.

Another note related to TV commercial insertion:
Has anyone tried decoding the audio tones that come just before ESPN cuts
to a commercial?  It sounds like 4 or 5 of them, and they sound a lot
like DTMF.  Do they identify which commerials are comming, or how long
the break is?  If I was watching the direct satelite feed, would there be
more tones announcing the resumption of the program?
I recall these mostly from watching live games; don't recall if they
are always there.  Anyone have any info?

--------------------------------------------------------------------
Steve Tell					tell@cs.unc.edu
CS Grad Student, UNC Chapel Hill.
Former video guy, Duke Union Community Television, Durham, NC.