Server-side ad insertion (SSAI) is a technique where ads are stitched into the video content stream on a server before the stream is delivered to the viewer's device. From the CTV app's perspective, the stream looks like one continuous video — it cannot distinguish where the content ends and the ad begins.
This eliminates ad blockers (which work by detecting VAST calls from the client device) and removes the buffering pause between content and ad (since the ad is already part of the stream before the device receives it). Viewers experience seamless transitions from content to ad and back.
SSAI is also called DAI — Dynamic Ad Insertion — which is Google's branded term for their SSAI product. In India, JioHotstar uses Google DAI for SSAI; SonyLIV uses SpringServe (part of Magnite) for its ad insertion. Zee5 uses a mixed approach. Most FAST channels in India still use CSAI (client-side ad insertion) due to lower implementation cost, though this is changing as FAST inventory grows.
The trade-off: because the ad is stitched server-side, client-side measurement pixels may not fire correctly. Publishers using SSAI typically use server-side beaconing — pinging tracking URLs from the server rather than the device — to compensate. This means third-party verification vendors (IAS, DoubleVerify) must have server-side integrations with the publisher to measure SSAI inventory accurately.
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For the full technical breakdown, see the SSAI in CTV knowledge base article.