Archived from groups: alt.video.ptv.tivo (
More info?)
Randy S. wrote:
> needin4mation@gmail.com wrote:
> > Is there a signature one could look for programmatically for their
> > inhouse commercial skip (say that person was a programmer)? Maybe
> > that's legal?
> >
>
> There is a signature that indicates when commercial breaks begin. There
> isn't one for when they end, so you'd have to use another method. It
> could technically be done.
>
There actually isn't a signature at either end of a commercial break,
but a broadcast tape is delivered with "open blacks," meaning the show
has a section of black in between acts that is as long as the
commercials are supposed to be.
(Aside - master recordings are "closed black," meaning the show dips to
black, then comes back up again 1 frame later, so the running time is
shorter than 1 hour (for a 60 minute show) because the space for
commercials is missing. Broadcast masters are created from the archive
master by "opening up" the blacks - inserting zero black (as in zero on
a scope), the length of which is determined by the broadcaster (it
could change) into the act breaks.)
So - the broadcaster plays the tape, and at the exact moment the show
drops to zero black another tape, already cued up, is switched to.
This tape has the commercials on it. The show tape, running zero
black, is still spinning, and as the last commercial ends the signal
switches back to the master, where the black is ending and the show
continues.
(of course some bigger broadcasters are using disc storage now, but the
shows are put together the same way.)
The important thing here is zero black. In NTSC zero black is
considered illegal, although there are no technical limitations to
broadcasting it. Assuming a decent signal, a device can easily detect
zero black and assume that it's the start, or end, of a commercial
break.
Unfortunately, some shows (or some show editors) will have their AVID
set incorrectly and, if there's a dip to black in the body of the show,
they will dip to zero instead of 10 units. Nobody is going to reject a
master produced this way, but it will trigger any commercial detection
device into thinking an ad has started.
And, of course, some networks now cut out of shows to a bumper, then
cut to a commercial. No zero black.
So it's tricky. I'd rather just use a 30 second skip.
/freepages.genealogy.rootsweb.com/~charlieh/
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