Re: Fwd: Re: Signal Transmission and Delay

[dan.strassberg@att.net]

There is at least one system being offered for sale to 
TV broadcasters that does real-time video time 
compression. The purpose is to allow local stations to 
insert at least one extra 30-second spot per half hour--
and greater compression is possible. The spot goes in 
first and the program begins delayed by 30 seconds (can 
be done in solid-state memory or hard disk). Then over 
the course of the half hour, frames are deleted until 
the program ends in sync with the network feed.

At 30 frames/sec, you need to delete 900 frames to make 
up for the 30-sec local spot. The trick is to delete 
audio during pauses but not make the speakers'/actors' 
lips appear to be out of sync with the sound. I don't 
know how far the picture and sound can be out of sync 
before the problem becomes noticeable. If 30 msec (the 
time of one frame) is imperceptible, the problem does 
not sound too difficult, but if the permissible time is 
a lot shorter, the algorithms could get interesting.
--
dan.strassberg@att.net
617-558-4205
eFax 707-215-6367

>  Speaking of delays, something unusual happens when Boston's WCVB-TV and 
> Manchester, NH's
> WMUR-TV take the ABC feed of the evening news at 6:30 pm Saturdays and 
> Sundays...
> the news on WCVB is shown about a minute-and-a-half to 32 minutes ahead of WMUR.
> If you're watching on the Boston channel and you miss something, flip to WMUR 
> and
> it will pop up again a short time later!  Am I the only one to notice this?
> And why and how do they do it?
> 
> Laurence Glavin
> Methuen, MA--
> 
> --------- Forwarded Message ---------
> 
> DATE: Thu, 25 Jul 2002 21:34:04
> From: Larry Weil <kc1ih@mac.com>
> To: "Daniel Murphy" <danmurph@worldnet.att.net>,"Boston Radio Interest Group" 
> <boston-radio-interest@bostonradio.org>
> 
> At 09:09 PM 7/25/02 -0400, Daniel Murphy wrote:
> 
> >This is a question for the more technical among you. I've noticed that when
> >listening to a syndicated show on a distant station, and then quickly tuning
> >in the same show on a Boston station, that there is a 1 to 2 second delay on
> >the Boston station. I was wondering why this happens, and more generally,
> >how is a syndicated show actually sent to stations where it is broadcast
> >locally.
> 
> If it's done the same in radio as it is in TV, the show is sent in advance 
> by satellite and recorded by each station.  Each station then rolls the 
> tape (or hard drive server) at it's air time for that program.  As for why 
> the Boston stations would roll a second or two later than other stations, I 
> don't know.
> ---
> Larry Weil
> Lake Wobegone, NH
> 
> 
> --------- End Forwarded Message ---------
> 
> 
> 
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