As subscriber counts for digital-cable services continue to rise, so do the reasons for offering local advertisements on digital channels. More boxes mean more eyeballs. More eyeballs mean more potential to attract, say, the ads of the local garden shop to HGTV, or those of the local golf store to the Golf Channel.
Already happening, right?
Alas. As with so many moving parts in the "digital transition," the old ways don't blend with the new ways. It turns out that inserting local ads into digital channels isn't the same as inserting local ads into analog channels.
Here's one example: The video servers that hold today's local ads did
save cable operators zillions in space and operational expenses, tied up in those cantankerous video tape recorders of yore.
Yet, those servers don't yet splice their contents into the channels of the digital tiers.
That's because the methods to trigger and launch an ad into a digital channel are still under construction.
That brings us to this week's translation: Digital Program Insertion, or "DPI."
In essence, DPI describes how to splice pieces of digital video into other pieces of digital video – like an ad into a TV show. It grew out of the SCTE's Digital Video Subcommittee, and straddles two technical standards: ANSI/SCTE 30 and 35 (coffee recommended.)
Understanding DPI requires a brief stroll through past and present workings of analog ad insertion. Remember those "doodley-doot" sounds that used to precede the cutover to the 30-second spots of local advertisers? About 15-20 years ago?
Lose the tone
Those four quickly uttered beeps, known as "cue tones," came from individual networks. They conveyed commands to those banks of video tape recorders, telling them to start playing a grouping of 30-second local ads. Near the end of the local commercial break, the beeps came again, telling the VTRs to stop, and switch back to the network feed.
After a while, though, the tones became Pavlovian. They taught viewers to walk to the kitchen, or to the bathroom, or to do whatever we do when we don't feel like watching Big Al repeat that he really does sell carpet cheaper. So, the tones were moved to a spectral area that TVs can't hear, known as "subcarrier audio."
That's pretty much the way it is today, except that the tones cue up the spots housed on video servers, not on VTRs.
Analog cue tones came from the same technology that makes the beeps when you dial digits on your telephone. They're known as "DTMF tones," which stands for "Dual Tone Multi-Frequency."
DTMF tones mean about as much to a digitized, compressed stream of video packets as an orange means to a bicycle. Bits just don't have the right ears for analog cue tones.
Inserting digital ads into digital programs requires two things, fashioned in principle by the SCTE standards. One is a cue trigger, inserted by a "cue message injector" into the MPEG-2 bit stream. The trigger comes from those digital networks interested in providing local ad avails.
The second is a "splicer," necessary to find the right places to jump into, and out of, an ongoing digital bit stream, as it makes its traverse from headend, to set-top box.
There is an alternative to DPI, but most technologists greet it with that scrunched up face that says "well, yes, maybe — if you're rich, or nuts." It involves taking each incoming digital network back to analog, inserting the ads at the right time, then re-encoding the channel back to digital.
And, for HDTV channels, there is no "going back to analog." It's DPI or nothing.
Small handfuls of program networks are starting to work with digital cue tones. An increasing number of equipment manufacturers are springing up around splicers; many will participate in the fifth in a series of tests at CableLabs next week. All of that qualifies as useful momentum.
If it seems like this stuff should've happened four or five years ago, recall that the digital viewership ticker started in 1995 — and it started at one.
Understandably, advertisers like maximum eyeballs. To them it's a question of what has more potential: Those two in 10 cable homes watching digital services, or the other eight, watching analog cable?
Nowadays, digital cable subscribership is plowing slowly but steadily into a range that makes it more interesting to advertisers. Even if digital-video penetration plateaus at 50%, that's still about 30 million sets of American eyeballs.
That's a primer on DPI, and why it registers as "important stuff people are working on in the background."
Next time, more on how digital content gets spliced into digital bit streams.