SSAI (server-side ad insertion) stitches ads into the video stream on a server before it reaches the viewer's device. CSAI (client-side ad insertion) has the CTV app make a separate VAST request to an ad server at the moment of an ad break, then plays the returned ad video from a separate source.
The key differences:
- Ad blocking: SSAI inventory cannot be blocked — there is no client-side VAST call to intercept. CSAI inventory can theoretically be blocked by network-level tools, though CTV ad blocking is uncommon in India compared to desktop.
- Viewer experience: SSAI eliminates the buffering pause between content and ads because the ad is already part of the stream. CSAI typically has a small buffer as the device fetches and loads the ad video from a separate URL.
- Measurement: CSAI allows client-side pixels to fire normally, making third-party measurement simpler. SSAI requires server-side beaconing for measurement to work correctly — if the publisher has not set up server-side beacons, impression data from SSAI inventory can be undercounted by third-party vendors.
- Implementation cost: CSAI is simpler and cheaper for publishers to implement. SSAI requires more infrastructure (transcoding, stream manifest manipulation) and technical investment.
In India: JioHotstar and SonyLIV use SSAI. Most FAST channels and smaller AVOD publishers use CSAI. For advertisers, SSAI inventory typically delivers better completion rates and cleaner ad experiences, but buyers should confirm that server-side beaconing is in place before counting on accurate third-party measurement data from SSAI publishers.
Related questions
For a full technical comparison, see the SSAI in CTV knowledge base article.