ALMOST 10 YEARS AGO, THIS COLUMN INVESTIGATED THE FRAUGHT ridden
life of the interactive-TV trigger and its taxing journey
from origination to TV screen. “Like salmon, triggers are
born with a mission: To make a difficult journey, perhaps
with a tryst near the end. If they’re lucky. Then, it’s over,” the
column noted.
Back then, we were talking about ITV triggers in terms
of “ATVEF” (pronounced as a word), the name of a Microsoft-
originated standard at the time. (And you thought
“EBIF” was bad.)
Then and now, “triggers” are the clickable things that
appear on the TV screen, hoping to be bright and sparkly
enough to entice viewers to click.
This was back in the days when interactive TV triggers
slipped into the vertical blanking interval of analog TV
signals — the place where closed-captioning data rode.
Digital ITV was still fairly new.
Then and now, the matter of trigger transit safety is
huge. So much so that these days, in the engine rooms of
interactive TV and EBIF, you hear people talking about “pipe
cleaners.”
EBIF stands for Enhanced TV Binary Interchange
Format. Just the inclusion of the word “binary” should
be an indicator that it’s teeny — written tightly, on
purpose, so as to reach as many fielded set-top boxes
as possible (25 million this year, of a total potential
footprint of 50 million-plus).
But just because EBIF apps are small (about 150 Kilobits
per second, rough numbers) doesn’t mean they’re any less
vexed by transit issues. Think about it: Being the clickable
thing on the screen means being squirted into a video bit
stream, blasted up into geosynchronous orbit (or injected
into a terrestrial fiber backbone), received, processed and
resent to homes.
The “pipe cleaner” talk, then, is about how to keep that
whole transit path clear of debris and drop points.
Technically, pipe-cleaning is a workflow. It involves
plunking a data feed on top of a video stream’s primary
audio and video packet identifiers, or PIDs, at the content
origination point. (For the advanced class, this involves
the use of a special scheduler, which talks to a special data
carousel to create an additional MPEG Transport Stream
containing EISS and DSM-CC PIDs.)
Without pipe-cleaning, triggers run the risk of getting
squished or dropped somewhere along the way, which
means they don’t get to the TV screen. Not good.
Key places to start jabbing the pipe cleaner, if you’re the
one in charge of degunking: Satellite receivers with analog
outputs, certain re-encoding points, and in those dense
quadrature amplitude modulation multiplexes.
Stumped by gibberish? Visit Leslie Ellis atwww.translationplease.
com.
