How does client-side ad insertion work on CTV?

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Last updated: April 8, 2026

Quick Answer: Client-side ad insertion (CSAI) on connected TV (CTV) works by dynamically inserting targeted ads into video streams at the viewer's device rather than at the server. This approach enables real-time personalization based on user data, such as demographics or viewing history, and allows for more precise ad measurement and optimization. CSAI typically uses technologies like the Video Ad Serving Template (VAST) and the Interactive Media Ads (IMA) SDK to manage ad delivery and playback. According to industry reports, CSAI adoption has grown significantly, with over 60% of CTV ad inventory expected to use client-side insertion by 2025, driven by demand for better targeting and reduced latency.

Key Facts

Client-side ad insertion (CSAI) dynamically inserts ads at the viewer's device in real-time, reducing latency compared to server-side methods.
CSAI enables personalized ad targeting on CTV using user data like demographics, with over 60% of CTV ad inventory projected to use it by 2025.
Technologies such as VAST (Video Ad Serving Template) and IMA SDK (Interactive Media Ads Software Development Kit) are commonly used for CSAI implementation.
CSAI improves ad measurement accuracy by allowing real-time tracking of impressions and viewer engagement metrics.
The shift to CSAI on CTV began gaining traction around 2018, driven by the rise of streaming services and demand for addressable advertising.

Overview

Client-side ad insertion (CSAI) is a method for delivering targeted advertisements in video content on connected TV (CTV) platforms, such as smart TVs and streaming devices. Unlike traditional server-side ad insertion (SSAI), which embeds ads into the video stream before it reaches the viewer, CSAI inserts ads dynamically at the client device, such as a Roku or Apple TV. This approach emerged in the late 2010s, around 2018, as CTV viewership surged, with over 80% of U.S. households using CTV by 2023. CSAI leverages the growing demand for addressable advertising, which allows ads to be tailored to individual viewers based on data like location or viewing habits. It addresses challenges in the CTV ecosystem, such as the need for real-time ad decisions and improved measurement, with industry adoption accelerating due to standards like those from the Interactive Advertising Bureau (IAB).

How It Works

CSAI on CTV operates through a multi-step process that begins when a viewer requests video content from a streaming app. The app fetches the main video stream and, simultaneously, requests ad opportunities from an ad server using protocols like VAST (Video Ad Serving Template). Based on user data—such as cookies or device IDs—the ad server selects relevant ads in real-time, often within milliseconds. These ads are then inserted into the video playback at designated break points, managed by software like the IMA SDK, which handles ad playback and tracking. This method reduces latency compared to SSAI, as ads are loaded locally, and enables dynamic ad replacement, allowing for updates based on viewer behavior. For example, a sports app might insert different ads during a live game based on the viewer's location or past interactions.

Why It Matters

CSAI matters because it enhances the CTV advertising experience by enabling more personalized and measurable ad campaigns. For advertisers, it offers better targeting capabilities, increasing the likelihood of engagement and higher return on investment (ROI), with studies showing that targeted CTV ads can boost conversion rates by up to 30%. For viewers, it means fewer irrelevant ads and a smoother streaming experience due to reduced buffering. In the broader media landscape, CSAI supports the growth of programmatic advertising on CTV, which is projected to account for over $20 billion in ad spend annually by 2024. It also addresses privacy concerns by allowing more control over data usage compared to some server-side methods, aligning with regulations like GDPR and CCPA.