When a CTV ad appears on your screen, nothing about it feels technical.
There’s no loading spinner. No awkward pause. No visible handoff between the show and the commercial.
The ad just plays.
That smoothness hides one of the most important pieces of infrastructure in modern streaming: Server-Side Ad Insertion, better known as SSAI.
Most advertisers never see it. Many don’t know it exists. But SSAI quietly determines how CTV ads are delivered, how they’re measured, and why the channel behaves so differently from traditional digital video.
The Problem SSAI Was Built to Solve
Early streaming platforms tried to serve ads the same way websites did.
The app would pause the content, request an ad, wait for it to load, play it, then resume the show. On desktops and phones, that approach mostly worked.
On TVs, it didn’t.
Buffering was common. Ad requests failed. Screens went black. Viewers abandoned streams. Advertisers paid for impressions that never really played.
CTV needed a delivery method that felt as reliable as broadcast television, but still allowed digital targeting and measurement.
SSAI was the answer.
What Actually Happens When You Press Play
From the viewer’s perspective, watching a CTV ad feels passive. Behind the scenes, it’s anything but.
When someone starts a show on a streaming app, the platform doesn’t send a raw video file to the TV. Instead, it assembles the stream dynamically.
As the content plays, the server already knows where ad breaks belong. When it reaches one of those moments, it doesn’t ask the TV to fetch an ad. It does the work itself.
The server:
Identifies the ad opportunity
Runs the ad decisioning process
Selects the winning ad
Stitches that ad directly into the video stream
By the time the stream reaches the TV, content and ads are already fused together into a single, uninterrupted feed.
To the device, there’s no difference between the show and the commercial. It’s all just video.
Why This Changes the Viewing Experience
This is why CTV ads feel more like traditional TV than digital video.
There’s no visible handoff because nothing is happening on the device. No extra requests. No separate ad player. No opportunity for something to fail mid-stream.
That’s also why:
Ads are effectively unskippable
Playback is consistent across devices
Buffering during ad breaks is rare
SSAI brings broadcast-level reliability to internet-delivered video.
That seamless experience comes with a trade-off.
Because ads are stitched into the stream before they reach the device, the TV has less visibility into what’s happening at the individual ad level. There’s no click event, no JavaScript firing, no pixel loaded in a browser.
This is why CTV measurement looks different.
Instead of clicks and last-touch attribution, SSAI environments rely on:
Completion rates
Household-level exposure
View-through attribution
Incremental lift analysis
It’s not a limitation of CTV as a channel. It’s a direct consequence of how SSAI works.
Where SSAI Sits in the CTV Ecosystem
SSAI quietly connects nearly every layer of the CTV stack.
Content platforms depend on it to protect the viewing experience.
SSPs rely on it to fill ad breaks efficiently.
DSPs compete for impressions that will be stitched into live streams.
OEMs use SSAI data to understand what households actually watched.
Even when advertisers don’t interact with SSAI directly, every CTV impression they buy flows through it.
It’s infrastructure, not a feature. Which is why it’s rarely discussed — and constantly used.
Why Advertisers Should Care
Understanding SSAI changes how you interpret performance.
It explains why:
CTV completion rates are so high
Viewability is often assumed, not measured
Impression timing matters more than clicks
Attribution windows look different than social or search
Advertisers who treat CTV like display video often get confused by the data. Advertisers who understand SSAI know what questions to ask — and which benchmarks actually make sense.
The Bottom Line
Server-Side Ad Insertion is the quiet engine behind Connected TV.
It’s why CTV ads feel like television but behave like digital. It’s why delivery is smooth, measurement is different, and performance conversations require a different frame of reference.
You may never see SSAI in a dashboard or proposal, but every CTV ad you run depends on it.
Once you understand how it works, the rest of the CTV stack starts to make a lot more sense.