In CSAI, the player coordinates the ad break. At a pre-roll, mid-roll, or post-roll cue, the player pauses content, contacts an ad server (typically via the IMA SDK or another VAST client), receives an ad VAST response, plays the ad, then resumes content. The ad runs as a separate playback session — potentially a different player instance, certainly a different network request, often a different decoder configuration.
CSAI's appeal is flexibility and control. The ad decisioning happens at request time per player, so geographic, behavioural and time-of-day targeting can be applied without re-rendering manifests server-side. Mid-roll insertion can be triggered by viewer events (pause, replay) rather than just scheduled markers. Ad analytics — viewability, click-through, completion — can be measured by the player without needing server-side cooperation.
CSAI's weaknesses are ad blockers (browser extensions easily detect IMA SDK and ad-server hostnames and block them), worse viewer experience (visible transition between content and ad players), and complexity on cross-platform deployments (different ad SDKs for web, iOS, Android, smart TVs). The 2026 trend in tier-1 OTT is server-side SSAI for live and FAST, with CSAI retained for specific VOD inventory where flexible targeting matters more than blocker resistance.
