What Are CSAI, SSAI, and SGAI?

The three dominant CTV ad insertion technologies each reflect a different balance between viewer experience, advertiser needs, and technical complexity. CSAI handles everything client-side, SSAI stitches ads server-side, and SGAI combines server-guided signaling with client-side rendering.

Client-Side Ad Insertion (CSAI) places all ad decision-making and rendering responsibility on the viewer's device. When the video player encounters an ad break, it independently contacts an ad server, retrieves the appropriate ad creative, and plays it locally. CSAI gives advertisers full control over measurement because ad playback happens on the client. The tradeoff is reliability: ad blockers can intercept client-side ad requests, playback transitions can produce visible buffering, and implementation varies across the fragmented CTV device ecosystem.

Server-Side Ad Insertion (SSAI) moves the ad insertion process entirely to the server. Before the video stream reaches the viewer, the ad server stitches selected ad creatives directly into the content stream, producing a single continuous video file. This eliminates buffering at ad transitions, defeats ad blockers, and provides a consistent experience across all devices. However, SSAI requires generating unique streams for each viewer, dramatically increasing CDN and encoding costs. Measurement is also degraded because the client player has no awareness of which segments are ads.

Server-Guided Ad Insertion (SGAI) emerged as a hybrid that captures the advantages of both. The server creates a non-viewer-specific content manifest with SCTE-35 markers indicating ad opportunities. This manifest is cached at the CDN for efficient delivery. When a viewer's device reaches an ad marker, it sends a personalized request to the ad decision server and handles ad playback locally. The result is server-level scalability, client-level personalization, and accurate client-side measurement.

How Do CSAI, SSAI, and SGAI Compare Feature by Feature?

SGAI leads in the combination of ad blocker resistance, real-time personalization, measurement accuracy, and low latency — areas where CSAI and SSAI each have significant weaknesses.

Key differences: CSAI has low ad blocker resistance while SSAI and SGAI are both high. Playback quality is variable with CSAI but excellent with both SSAI and SGAI. Personalization is real-time with CSAI and SGAI but limited with SSAI. Measurement accuracy is high with CSAI and SGAI but low with SSAI. CDN cost is low for CSAI and SGAI but high for SSAI (unique stream per viewer). Live latency impact is medium for CSAI, high for SSAI (15-30s delay), and low for SGAI. Interactive and pause/overlay ad support is available with CSAI (limited) and SGAI (full) but not with SSAI.

When Should You Use Each Technology?

The choice depends on content type, scale, and business priorities. Each technology has an ideal use case where it outperforms the others.

Use CSAI when you are operating primarily on web and mobile platforms, your audience is not ad-blocker heavy, measurement precision is your top priority, and you need maximum flexibility in ad creative formats.

Use SSAI when you are serving long-form VOD content on CTV devices, ad blocker resistance is essential, and personalization requirements are modest. SSAI continues to be the default for many FAST channels and VOD libraries.

Use SGAI when you are monetizing live content (especially live sports), need real-time ad personalization on CTV, want to support interactive or non-standard ad formats (pause ads, overlays, shoppable experiences), and are optimizing for both viewer experience and advertiser ROI.

Hybrid strategies are increasingly common. Many platforms run SSAI for their CTV/FAST inventory and SGAI for low-latency live streams and mobile/web delivery.

What Are the Economics of Each Ad Insertion Approach?

SSAI is the most expensive at scale due to per-viewer stream generation. SGAI's cached manifest approach keeps infrastructure costs largely fixed regardless of concurrent viewer count.

During a major live event with millions of concurrent viewers, SSAI requires encoding and delivering a unique stream for each viewer session — a cost that scales linearly and can become prohibitive during peak events. SGAI's manifest is generated once and cached at the CDN. Individual ad requests from viewers are lightweight API calls to the ad decision server.

CSAI has the lowest infrastructure cost but the highest hidden cost in lost revenue — ad blockers can reduce effective fill rates by 15-30% on platforms with tech-savvy audiences.

For a platform serving 5 million concurrent viewers during a Sunday NFL game, the infrastructure cost difference between SSAI and SGAI can exceed six figures per event.

How Do You Migrate from SSAI to SGAI?

Platforms currently running SSAI can transition to SGAI incrementally by running both systems in parallel, starting with a subset of inventory.

The recommended migration path involves starting SGAI on mobile/web first, then CTV, validating measurement parity, and gradually shifting traffic as confidence builds. Key considerations include player SDK updates (SGAI requires client-side ad rendering capabilities), ad server configuration (manifest must include SCTE-35 markers), CDN caching rules, and measurement validation across all device types.

Frequently Asked Questions

Can I run SGAI and SSAI simultaneously?

Yes. Many platforms use a hybrid approach, running SSAI for certain inventory types (VOD, FAST) and SGAI for live content and mobile/web. This is the most common transition strategy.

Does SGAI require a specific video player?

SGAI requires a video player that supports manifest-based ad signaling and client-side ad resolution. Most modern CTV player SDKs (including those from StreamLayer, Bitmovin, and others) support SGAI.

Which is better for live sports — SSAI or SGAI?

SGAI is significantly better for live sports. SSAI's 15-30 second stitching delay is problematic for live content where ad breaks are unpredictable and latency-sensitive. SGAI's real-time ad resolution and event-triggered insertion capabilities make it the preferred choice for live sports monetization.