Inside the Signal: How a “TV Impression” Becomes Data

A CTV impression looks deceptively simple.

An ad plays on a screen. The viewer watches. The campaign reports delivery. CPMs are calculated. A report gets sent.

But that clean outcome masks a messy truth: CTV impressions are not events. They’re interpretations.

Unlike web or mobile, where an impression is tied to a browser firing code, CTV lives in a world where almost nothing happens on the device itself. No JavaScript. No click listeners. No cookies. No deterministic user IDs.

So how does a single ad exposure turn into something a DSP can report, an SSP can bill, and an advertiser can trust?

It starts upstream.

In CTV, the impression is effectively created at the moment of decision, not the moment of viewing.

When an ad break approaches, the server-side systems decide which ad will be stitched into the stream. That decision triggers a cascade of logs:

At this point, the impression is already “real” in the ecosystem, even though the viewer hasn’t seen a frame yet.

This is the first mental shift advertisers need to make.

CTV impressions are probabilistic promises, not device-confirmed events.

Once the stream reaches the TV, the platform can’t observe much.

There’s no reliable way for the device to say “the user watched exactly 27.4 seconds.” Instead, platforms rely on indirect signals:

None of these confirm attention. They confirm stream continuity.

This is why CTV reports look clean. And why they should always be read with context.

High completion rates don’t mean high engagement. They mean the stream wasn’t interrupted.

That distinction matters.

On the web, viewability exists because ads can be hidden, minimized, or scrolled past.

On CTV, the ad is the screen.

There’s no fold. No tab switching. No background playback. So the industry made a trade-off: assume viewability in exchange for reliability.

This is not a shortcut. It’s a structural decision driven by how SSAI works.

Once you understand that, a lot of common CTV questions disappear:

Because the system was never built to observe behavior. It was built to guarantee delivery.

If CTV impressions don’t come from the device, where does performance data come from?

From correlation, not causation.

DSPs and measurement partners look for patterns:

CTV performance is inferred by what happens next, not what happens during the ad.

This is why CTV lives closer to brand science than direct response, even when it drives performance outcomes.

Many advertisers approach CTV expecting digital precision.

What they find instead is statistical confidence.

That’s not a flaw. It’s the reality of delivering ads through a broadcast-like medium over the internet.

The CTV stack doesn’t pretend to know everything. It focuses on what it can know reliably:

Once you stop looking for clicks and start looking for impact, the system starts to make sense.

A CTV impression isn’t a pixel firing.

It’s a negotiated agreement between systems that trust each other to deliver video at scale.

Understanding that shift is the difference between fighting the data and using it correctly.

And once you see how the signal is constructed, you stop asking whether CTV “works” and start asking the only question that matters:

What changed after people saw the ad?