Glossary
SSAI (server-side ad insertion)
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Server-side ad insertion is the technique of stitching advertisements into a video or audio stream on the server before delivery, so that the player receives one continuous stream rather than switching to an ad at runtime, with the consequence that ad requests, impression tracking and viewability signals may originate from the server rather than the viewer's device.
OpenRTB 2.6 flags it on the impression with imp.ssai: "0 = status unknown, 1 = all client-side (i.e., not server-side), 2 = assets stitched server-side but tracking pixels fired client-side, 3 = all server-side" (OpenRTB 2.6, section 3.2.4). The flag matters because a bidder sees the SSAI server's IP and user agent instead of the device's unless the platform forwards them, which affects fraud detection, geo-targeting and frequency capping, and because tracking fired from the server cannot measure viewability the way a client can. SupplyChain v1.1, in public comment to 21 August 2026, adds SSAI platforms to the schain as custody-taking nodes with hp=0, so buyers can see when a stitching service sat between the publisher and the exchange (IAB Tech Lab, 23 June 2026).
SSAI is the default for connected TV and live streams, where ad pods must play without buffering and where ad blockers cannot reach the server. IAB Tech Lab's 2026 roadmap lists CTV signal work across OpenRTB, VAST and SIMID and a Concurrent Streams API for live events as part of the same portfolio (IAB Tech Lab 2026 roadmap letter). An independent CTV ad server, as opposed to one owned by the distributor, is the topic of VAST and CTV ad serving.
Example: "imp": [{ "id": "1", "video": { "mimes": ["video/mp4"], "minduration": 15, "maxduration": 30, "plcmt": 1 }, "ssai": 2 }] tells bidders the creative will be stitched server-side but tracking pixels will fire from the client.
Related: SupplyChain object, ad server, bid request, OpenRTB.
Source: IAB Tech Lab, OpenRTB 2.6, Imp.ssai; SupplyChain v1.1 (June 2026).
Each term page: Author: [named author, title, profile link]. Published: [date]. Last updated: 18 October 2026.