SSAI vs CSAI for Live News & Broadcast: Ad Fill Rate Comparison

SSAI (server-side ad insertion) stitches ads directly into a live video stream on the server before it reaches the viewer, while CSAI (client-side ad insertion) has the video player request and splice in ads separately in the browser. For live news and broadcast, SSAI consistently delivers higher ad fill rates and far less ad-break rebuffering than CSAI.

If your live news stream loses viewers every time an ad break starts, the cause is almost always where the ad gets inserted, not which ad server you use. This guide compares the two approaches in detail and explains why fill rate and rebuffering behave so differently between them.

What Is CSAI (Client-Side Ad Insertion)?

CSAI (Client-Side Ad Insertion)

The video player itself requests the ad from an ad server, then switches from the content stream to a separate ad stream, and back again once the ad finishes. The ad request, the ad decision, and the stream switch all happen inside the viewer's browser or app.

This is how Google IMA SDK and most VAST/VPAID-based integrations work by default — the player calls an ad tag, receives a VAST response, loads the creative, and plays it as a separate video element or stream.

What Is SSAI (Server-Side Ad Insertion)?

SSAI (Server-Side Ad Insertion)

Also called dynamic ad insertion (DAI). The ad decision and stitching happen on the server: an SSAI stitcher (AWS MediaTailor, Google DAI, Yospace, Broadpeak) rewrites the HLS or DASH manifest so ad segments are already part of the single stream the player requests. The player never knows an ad break happened — it just keeps pulling the next segment.

Ad Fill Rate Comparison: SSAI vs CSAI

Why Ad Fill Rate Drops with CSAI on Live News

Live news has a specific problem CSAI struggles with: viewers on the same channel hit an ad break at the same moment, all firing ad requests within seconds of each other. Under that spike:

• Slow or overloaded ad servers return no-fill responses under load, which CSAI reports as lost impressions.
• Mobile and in-app browsers frequently block third-party ad-server requests outright.
• The player has to buffer a new manifest for the ad creative, which on a live edge stream often means a visible stall.
• CTV apps — a large share of live news viewing — often can't run a full VAST/VPAID client at all, so the ad break is skipped or shows a blank slate.

How SSAI Improves Fill Rate for Live Broadcast

Because the SSAI stitcher makes the ad decision server-to-server, it isn't affected by the viewer's browser, ad blocker or CTV SDK limitations. The stream the player receives already has the ad stitched in — so as long as the ad decision server itself returns an ad, it plays. This removes an entire category of client-side fill rate loss, without changing anything about the ad server or campaigns feeding it.

CTV Compatibility Considerations

For live news publishers, CTV apps are usually where the fill rate gap is worst — Roku, Fire TV, Apple TV and Android TV apps vary widely in native ad SDK support. SSAI sidesteps this: the CTV app plays one HLS or DASH stream and never has to implement ad logic itself, which is why most CTV-first broadcasters move to SSAI as soon as CTV viewership becomes material.

Migration Path from CSAI to SSAI

1. Audit your current ad stack — ad server, VAST version, and which platforms currently run CSAI vs no ads at all.
2. Choose an SSAI stitcher — AWS MediaTailor, Google DAI, Yospace or Broadpeak, based on your existing AWS Elemental footprint and ad server compatibility.
3. Wire up SCTE-35 cue processing for live streams so ad breaks trigger accurately at the frame level.
4. Validate manifest stitching on each platform — HLS discontinuity tags and DASH period insertion both need to match your existing codec/bitrate ladder.
5. Run CSAI and SSAI in parallel for a measurement window, comparing fill rate and rebuffering before fully cutting over.

Frequently Asked Questions