Ad Architecture
CSAI (Client-Side Ad Insertion)
Reviewed by Sonu · OTT & StreamingLast updated: 2026-06-30
CSAI (Client-Side Ad Insertion) inserts ads on the viewer's device during playback — the player pauses content, fetches and plays the ad, then resumes. It's flexible and easy to set up but more exposed to ad blockers than server-side insertion.
Enveu take
CSAI is the quickest way to start monetizing, but ad blockers and the content-to-ad transition are its weak points — most platforms graduate to SSAI as scale and fill matter more.
AdvertisingAd insertionPlayback
Where it fits in the OTT stack
Player (client)→Ad SDK→Ad Server→Content
How it works
- The player reaches an ad break (pre/mid/post-roll).
- A client-side ad SDK requests an ad from the ad server (VAST/VMAP).
- The player pauses content and plays the returned ad.
- Content resumes after the ad completes.
Key components
- Client ad SDK (e.g. IMA)
- VAST/VMAP ad tags
- Ad server / demand source
- Player integration per platform
Performance impact
- Fast to implement and flexible per device
- Exposed to ad blockers that skip the SDK
- Visible content-to-ad switching can hurt experience
Common issues
- Ad blockers reducing fill
- Buffering at the content-ad transition
- Inconsistent behavior across player platforms
When to use it
- Early monetization or where SSAI isn't yet in place
- Cases needing flexible, per-device ad logic
Signals to monitor
- Ad fill rate and completion
- Transition buffering
- Ad-block rate
Real-world example
Starting with CSAI, then scaling to SSAI
A platform launched ad monetization quickly with client-side ads.
Challenge
- Ad blockers cut fill on web
- Content-to-ad transitions stuttered
Action taken
- Kept CSAI for fast iteration, then moved high-value inventory to SSAI
Outcome
Fill and completion improved on premium inventory while keeping CSAI's flexibility where it helped.
Frequently asked questions
What is client-side ad insertion?
CSAI inserts ads on the viewer's device — the player pauses content, requests and plays an ad via an ad SDK, then resumes. It's flexible but more exposed to ad blockers.
What's the difference between CSAI and SSAI?
CSAI inserts ads in the player on the device; SSAI stitches ads into the stream on the server before delivery. SSAI resists ad blockers and gives smoother playback; CSAI is simpler and more flexible.
Is CSAI affected by ad blockers?
Yes — because the ad request happens client-side, ad blockers can intercept it and reduce fill, which is a key reason platforms move premium inventory to SSAI.
When is CSAI a better choice than SSAI?
CSAI is simpler to implement, supports interactive formats and clickthroughs more easily, and gives the player full control of the ad experience. It suits web and mobile where interactivity matters more than ad-block resilience or seamless CTV playback.
Why do ads buffer or fail with CSAI?
Because the player makes a separate ad request mid-playback, it's exposed to ad-server latency, wrapper chains and blockers. Deep VAST wrapper chains and slow ad responses are the usual causes of visible stalls at the break.
Build it with Enveu
Insert ads, server- or client-side
Enveu supports SSAI and CSAI with VAST/VMAP and full ad analytics across every device.