SSAI (Server-Side Ad Insertion)

SSAI (also called DAI, dynamic ad insertion) stitches ads directly into the video stream on the server side before the content ever reaches the player. The viewer's player has no idea it is watching an ad. From its perspective, the stream is one continuous flow of segments. No separate ad requests, no separate ad player, nothing for an ad blocker to intercept.

The way it works: when a viewer requests a stream, the SSAI service generates a personalized manifest. This manifest contains the normal content segment URLs, but at ad break points, it swaps in URLs for ad segments that match the viewer's targeting profile. The player just downloads segments in order, completely unaware that some are ads and some are content.

The CDN challenge with SSAI is interesting. Each viewer's manifest is unique because different viewers get different ads. That means manifests are essentially uncacheable, one per viewer per session. However, the actual media segments (both ad creatives and content) are shared across many viewers and cache beautifully. A popular ad creative might be served to millions of viewers from CDN cache. The content segments are identical for everyone.

Major SSAI providers include AWS Elemental MediaTailor, Google Ad Manager (DAI), Yospace, and Brightcove SSAI. Most work by sitting between your origin and CDN, intercepting manifest requests and rewriting them on the fly with personalized ad segment URLs.