An ad server is what delivers the actual ad to the viewer after the auction is won. It sits between the SSP (which ran the auction and picked the winner) and the viewer's device. Google Ad Manager is the dominant publisher ad server in India CTV.
There are two ways an ad server can deliver a CTV ad:
CSAI (client-side ad insertion): The video player on the viewer's device pauses content, makes a separate request to the ad server, fetches the ad from a CDN, plays it, then resumes content. Third-party measurement pixels can fire from the device. Downside: often causes a brief buffering pause between content and ad.
SSAI (server-side ad insertion): The ad is stitched into the video stream at the server level before the stream is delivered to the device. The viewer sees one continuous stream — content and ad play without any buffering transition. The device does not know an ad is being inserted. SSAI is used by JioCinema, Hotstar, and most premium India CTV publishers because it delivers a TV-like experience with no ad-loading pause.
The trade-off: with SSAI, third-party verification vendors (DoubleVerify, IAS) cannot fire tracking pixels from the viewer's device directly. Measurement relies on platform-reported metrics or SSAI-compatible integrations the publisher must explicitly enable. Impression discrepancies of 5-15% between the DSP count and the platform count are normal on India CTV campaigns — a direct result of SSAI delivery.
Full guide
For a complete explanation, read: CTV ad servers and SSAI: how ads are delivered to streaming TV