SSAI (server-side ad insertion), also called ad stitching, splices ads into the video stream at the server or edge, so the ads arrive as part of the same stream as the content. To the player, ad and content segments look identical — same format, same manifest timeline — which is exactly why SSAI resists ad-blockers and plays seamlessly, with no buffering at the ad boundary, on devices like smart TVs where client-side ad SDKs are weak.
The flow ties together several standards: SCTE-35 markers in the stream signal where an ad break may go; an ad decisioning service is called (speaking VAST/VMAP) to choose ads, often personalized per viewer; and the stitcher assembles a per-session manifest that weaves the chosen ads into the content. Because each viewer can get different ads, SSAI can fragment the CDN cache, so cache design and the split between shared content and per-user ads matter.
SSAI is the backbone of serious AVOD and FAST monetization; its trade-offs versus CSAI are seamlessness and block-resistance (SSAI) against simpler implementation and richer interactivity (CSAI).
