Glossary
CSAI
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Client-side ad insertion (CSAI) is a way of delivering video and audio ads in which the player on the viewer's device requests, loads and plays the ad and fires the tracking pixels itself.
In CSAI the player runs the ad break. At a cue point it calls an ad server, receives a VAST response, downloads the ad file, plays it, and sends impression and quartile beacons straight from the device. Because the device makes these calls, measurement vendors can run their scripts and read real device signals, which makes verification and viewability measurement simpler.
The weakness is the viewer's experience. Each break waits on network calls, so ads can buffer or fail, and ad blockers can stop the calls. Server-side ad insertion (SSAI) avoids this by stitching ads into the stream on a server, which is common in connected TV and live streaming.
OpenRTB 2.6 records which method applies in the impression's ssai field. A value of 0 means unknown, 1 means all client-side, 2 means assets stitched server-side with tracking fired from the client, and 3 means all server-side (IAB Tech Lab, OpenRTB 2.6, section 3.2.4). Buyers use the field to judge how far they can trust the device signals in a request.
Example: A news site's web video player reaches a mid-roll cue point and sends a request whose impression carries "ssai": 1. It receives a VAST tag and plays a 15-second ad. The impression pixel fires from the viewer's browser, so the advertiser's verification vendor can measure it directly. The server-side alternative is covered in SSAI and CTV ad serving.
Related terms: SSAI, VAST, VPAID, pod bidding, FAST channel.