If you operate a CTV platform, you have faced this decision: server-side ad insertion or client-side ad insertion? The choice affects everything from viewer experience and ad-blocker resilience to measurement accuracy and infrastructure costs. Yet the conversation around SSAI and CSAI is often reduced to oversimplified pros-and-cons lists that ignore the nuances of real-world deployment.
This guide breaks down how each method actually works, where each excels, and how to make the right decision for your specific platform, content mix, and business objectives.
What Is Server-Side Ad Insertion (SSAI)?
Server-side ad insertion, sometimes called ad stitching, is a technique where the ad creative is combined with the content stream on the server before it is delivered to the viewer's device. The viewer's player receives a single, continuous stream that includes both content and ads. From the player's perspective, there is no distinction between a content segment and an ad segment; it is all one manifest.
The process works like this: when a viewer initiates playback, the content delivery system identifies the ad break opportunities within the stream. It sends ad requests to the ad decision server, receives the selected creatives, transcodes them to match the content stream's specifications (codec, resolution, bitrate), and stitches them into the manifest. The viewer sees a seamless transition from content to ad and back again.
The Case for SSAI
SSAI's primary advantage is the viewer experience. Because the ad is part of the content stream, there is no buffering when transitioning into or out of an ad break. The player does not need to initialize a separate ad SDK, load a new video source, or negotiate a different CDN connection. The result is a television-quality experience that feels natural and uninterrupted.
The second major advantage is ad-blocker resistance. Because the ad is stitched into the content manifest at the server level, client-side ad blockers cannot distinguish between content segments and ad segments. They would have to block the entire stream to block the ads. For publishers concerned about ad-blocking adoption on CTV devices, this is a significant consideration.
SSAI also delivers consistent quality across devices. Because the server handles transcoding and manifest manipulation, the experience is uniform regardless of whether the viewer is watching on a Roku, Fire TV, Samsung smart TV, or any other device. The publisher does not need to maintain and test separate ad SDKs for each device platform.
SSAI delivers the experience viewers expect from television: seamless, buffer-free, and indistinguishable from the content itself. For premium CTV environments, this is not a luxury; it is the baseline.
SSAI's Trade-Offs
SSAI is not without challenges. The most significant is the difficulty of supporting interactive ad formats. Because the ad is part of the content stream, overlaying interactive elements such as clickable buttons, QR codes, or shoppable product carousels requires additional client-side logic that partially undermines the server-side approach. While solutions exist, they add complexity and are not universally supported across devices.
Reporting and measurement can also be more complex with SSAI. Since the client player does not distinguish between content and ad segments, traditional client-side tracking pixels and VPAID-based measurement do not work in their standard form. Instead, SSAI implementations rely on server-side beaconing and specialized tracking protocols. This works well with modern ad servers, but it requires buyers and measurement vendors to support server-side reporting methods.
Infrastructure cost is the third consideration. SSAI requires real-time transcoding capabilities, manifest manipulation servers, and CDN capacity to handle the stitched streams. For publishers with large-scale live content, the transcoding infrastructure alone can represent a meaningful cost center.
What Is Client-Side Ad Insertion (CSAI)?
Client-side ad insertion takes a fundamentally different approach. Instead of stitching ads into the content stream on the server, CSAI relies on an ad SDK or player plugin running on the viewer's device to handle ad playback. When the player reaches an ad break, it pauses the content stream, loads the ad creative from a separate source, plays it, and then resumes the content.
The workflow is familiar to anyone who has worked with web video advertising. The player detects an ad cue point, calls the ad decision server via VAST or VMAP, receives an ad response, loads and renders the creative using client-side resources, fires tracking events directly from the device, and returns to content playback when the ad completes.
The Case for CSAI
CSAI's strongest advantage is its support for rich interactivity. Because the ad SDK runs on the client device, it can overlay interactive elements, respond to user input, and render dynamic creative formats that would be impossible within a stitched stream. For advertisers investing in interactive CTV experiences, shoppable ads, or dynamic creative optimization, CSAI provides a more capable canvas.
Measurement is inherently simpler with CSAI. The client-side SDK can fire tracking pixels directly, count impressions at the device level, and integrate with standard measurement frameworks like VAST, VPAID, and OMID without server-side workarounds. This makes reporting more straightforward and reduces discrepancies between publisher and buyer impression counts.
CSAI also requires less server-side infrastructure. The publisher does not need real-time transcoding servers or manifest manipulation engines. The ad creative is loaded and played independently by the client, which can reduce backend complexity and cost, particularly for smaller publishers who lack the engineering resources for a full SSAI deployment.
CSAI's Trade-Offs
The viewer experience is CSAI's most significant weakness. The transition between content and ad requires the player to load a new video source, which introduces latency. On slower devices or congested networks, this latency manifests as buffering, black screens, or visible loading spinners at the start and end of each ad break. For viewers accustomed to linear television's seamless transitions, this can feel jarring.
Ad-blocker vulnerability is the second concern. Client-side ad requests are visible to ad-blocking software, and while CTV ad blocking is less prevalent than web ad blocking, it is growing. Any publisher building a long-term strategy must consider that client-side ad calls are inherently more exposed.
Device fragmentation creates additional challenges for CSAI. Each CTV platform has its own player implementation, SDK requirements, and rendering quirks. Maintaining and testing a client-side ad SDK across Roku, Fire TV, Apple TV, Android TV, Samsung Tizen, LG webOS, and various smart TV platforms is a significant ongoing engineering burden.
Key Decision Factors
Choosing between SSAI and CSAI is not a matter of one being universally superior. The right choice depends on your specific circumstances:
- Viewer experience priority: If delivering a television-quality, seamless experience is non-negotiable for your brand or audience expectations, SSAI is the clear choice.
- Device landscape: If you serve a fragmented audience across many CTV devices, SSAI's server-side normalization eliminates per-device complexity. If you primarily serve a single platform with a mature SDK, CSAI may be more practical.
- Measurement requirements: If your buyers demand standard client-side tracking and you lack the engineering capacity to implement server-side beaconing, CSAI provides an easier measurement path.
- Ad format strategy: If interactive or dynamic creative formats are central to your value proposition to advertisers, CSAI offers more native support for these capabilities.
- Scale and infrastructure: If you have the engineering resources and scale to justify SSAI infrastructure, the long-term benefits typically outweigh the costs. Smaller publishers may find CSAI more practical as a starting point.
The Hybrid Approach
Increasingly, the most sophisticated CTV platforms are not choosing one method exclusively. They are deploying both strategically based on content type, device capabilities, and buyer requirements. A hybrid approach might use SSAI for live content, where seamless ad insertion is critical and ad breaks are time-sensitive, while using CSAI for on-demand content, where interactivity opportunities are richer and the latency tolerance is slightly higher.
The hybrid model also allows publishers to accommodate buyer preferences. Some demand-side platforms have established workflows built around client-side measurement. Rather than forcing these buyers to adapt, a publisher can route their campaigns through CSAI while handling the rest of their demand via SSAI.
Live vs. VOD Considerations
Content type heavily influences the SSAI-versus-CSAI decision. For live content, SSAI dominates for good reason. Live ad breaks are time-constrained, often lasting exactly 120 or 180 seconds. There is zero tolerance for buffering or late ad loads because the content stream continues regardless. SSAI's ability to pre-stitch ads into the live manifest ensures that every second of the ad break is filled and the transition back to content is frame-accurate.
For VOD content, the calculus is more balanced. The ad breaks are not time-constrained in the same way, and the content stream can wait for the ad to load. This makes CSAI's latency penalty less critical. Meanwhile, VOD environments offer more opportunity for interactive ad experiences and personalized creative, playing to CSAI's strengths.
Impact on Programmatic
The ad insertion method affects programmatic execution in ways that are not always obvious. SSAI typically requires that ad decisions are made slightly earlier in the process because the transcoding and stitching steps take time. This means bid requests must be sent and resolved before the ad break begins, which can limit the use of real-time signals that only become available at the moment of playback.
CSAI, by contrast, can make ad decisions at the exact moment of playback, incorporating the most current bidding landscape and real-time signals. However, this comes at the cost of the latency introduced by the client-side ad loading process.
Modern SSAI implementations have narrowed this gap significantly by reducing transcoding times and implementing predictive ad decisioning that pre-fetches likely ad creatives before the break begins. But the trade-off between decision freshness and playback seamlessness remains a relevant consideration.
The Shigo Approach
At Shigo, we support both SSAI and CSAI within a unified platform, because we believe the choice should be driven by publisher needs, not platform limitations. Our architecture provides a single reporting and analytics layer that normalizes data across both insertion methods, eliminating the fragmented reporting that plagues publishers running separate SSAI and CSAI stacks from different vendors.
This unified approach means publishers can adopt a hybrid strategy without managing multiple vendor relationships, reconciling disparate data sources, or maintaining separate operational workflows. One platform, one truth, regardless of how the ad reaches the screen.
Practical Checklist: Making Your Decision
Before committing to an ad insertion strategy, work through these questions:
- What is your content mix? Heavy live content strongly favors SSAI. Pure VOD opens the door to CSAI or hybrid.
- How many device platforms do you support? More devices increase the value of SSAI's server-side normalization.
- What are your buyers demanding? Survey your top demand partners about their measurement and creative requirements.
- What is your engineering capacity? SSAI requires more server-side infrastructure; CSAI requires more client-side SDK maintenance.
- How important is ad-blocker resistance? If your audience skews younger or more technically savvy, SSAI's resilience matters more.
- Are interactive formats part of your roadmap? If so, ensure your chosen approach can support them, whether natively via CSAI or through overlay solutions on SSAI.
- Can your platform support both? If the answer is yes, a hybrid approach gives you the most flexibility to optimize per use case.
The SSAI-versus-CSAI question does not have a universal answer. But it does have a right answer for your platform, your content, and your business. The key is to evaluate the trade-offs honestly, resist the temptation to choose based on industry hype, and select the approach that aligns with your viewers' expectations and your advertisers' needs. In many cases, the answer is both.