What is the difference between SSAI vs CSAI ads?

According to eMarketer’s “US Digital Ad Spending Forecast,” in 2025, video streaming will dominate the US media, with ad spending projected to increase past $200 billion. Whether you’re binge-watching a series on an AVOD platform or catching a live NFL game, ads are everywhere, and how they’re delivered matters. Two key players in this space are SSAI (Server-Side Ad Insertion) and CSAI (Client-Side Ad Insertion), the backbone of modern video adtech. For US marketers, developers, and streaming providers, choosing between SSAI vs. CSAI isn’t just a tech decision. It’s a strategic one that can impact revenue, viewer experience, and campaign success.

So, what’s the difference between SSAI and CSAI? Which method fights ad blockers better? In this article, OTTclouds will break down SSAI vs. CSAI, explore their benefits and challenges, and help you pick the right ad insertion method for your business strategy. Let’s dive in.

Understanding ad stitching in CSAI and SSAI monetization methods

Ad stitching is a critical process in modern video advertising, enabling seamless integration of video content and advertisements. It plays a central role in two primary monetization methods: Client-Side Ad Insertion (CSAI) and Server-Side Ad Insertion (SSAI). While both approaches aim to deliver ads effectively, they differ significantly in handling ad stitching.

Ad Stitching in CSAI

In CSAI, ads are inserted on the viewer’s device. When an ad marker is detected, the video pauses and an ad is delivered. This method allows real-time targeting but is vulnerable to ad blockers and may cause playback interruptions.

Ad Stitching in SSAI

SSAI embeds ads directly into the video stream on the server side, creating a seamless viewing experience. It bypasses ad blockers and reduces buffering, making it ideal for OTT, CTV platforms, and FAST channels.

Both CSAI and SSAI are essential for delivering ads effectively while maintaining viewer experience. CSAI excels in targeting, while SSAI offers a seamless and resilient solution. As streaming services grow, both methods will continue to shape video monetization strategies.

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What are CSAI and SSAI? How does it work?

What is CSAI?

CSAI, or Client-Side Ad Insertion, is a method of delivering video ads where the video player on the viewer’s device handles ad requests and insertion. The player communicates directly with an ad server to stitch and display ads during playback. This approach allows for real-time ad personalization and precise targeting based on user data. It’s been around longer, so it’s widely supported across platforms like YouTube or mobile apps.

How does CSAI work?

• Ad Request: When the video player encounters an ad marker (e.g., pre-roll, mid-roll, or post-roll), it pauses the content and sends a request to the ad server.
• Ad Delivery: The ad server selects and delivers an ad based on user data, preferences, or campaign requirements.
• Ad Playback: The video player plays the ad and resumes the main content seamlessly.
• Ad Tracking: The player tracks metrics like impressions, interactions, and viewability to report to advertisers.

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What is Server-side Ad Insertion (SSAI)?

Server-Side Ad Insertion (SSAI), also known as ad stitching or dynamic ad insertion, is a technology that integrates advertisements directly into video streams on the server side before delivering them to viewers. Unlike Client-Side Ad Insertion (CSAI), where ads are fetched and displayed by the video player on the user’s device, the server does all the work, seamlessly stitching the advertisement into the content to feel like part of the broadcast.

How does SSAI work?

• Ad Detection and Request: When an ad break is reached in the video content, the server identifies ad markers embedded in the stream and sends a request to an ad server.
• Ad Selection: The server selects ads that match the video’s bitrate, frame rate, and audio settings to ensure smooth transitions between content and ads.
• Ad Stitching: Ads are dynamically stitched into the video stream, resulting in a continuous playback experience with no buffering or interruptions.
• Delivery: The stitched stream is delivered to the viewer’s device as a single file, bypassing ad blockers and ensuring consistent platform quality.

SSAI is widely used in OTT and connected TV platforms because it enhances user experience by eliminating pauses during ad breaks. It also simplifies ad delivery workflows and ensures ads are immune to ad-blocking software.

Key differences between SSAI vs CSAI

Server-side ad Insertion (SSAI) and Client-Side Ad Insertion (CSAI) are two primary methods for delivering video ads. Each has distinct mechanisms and implications for user experience, ad delivery, and performance.

Comparison table: CSAI vs. SSAI

Advantages and Disadvantages of CSAI

In CSAI, the video player on the user’s device is responsible for requesting and inserting ads during playback. When the content reaches a designated ad break, the player sends a request to an ad server, retrieves the ad, and plays it before resuming the main content. Your device does the heavy lifting—requesting, loading, and playing the ad.

Advantages:

• Interactivity: CSAI supports interactive ad formats, such as clickable or skippable ads, enhancing user engagement.
• Detailed Analytics: It allows for comprehensive tracking of user interactions, providing valuable data for performance reporting and ad optimization.

Disadvantages:

• Ad Blocking: Since ads are loaded on the client side, they are more susceptible to being blocked by ad blockers, potentially reducing ad impressions and revenue.
• User Experience: Ads may require additional buffering, leading to interruptions and a less seamless viewing experience.

CSAI real-world example

You’re streaming a workout video, and a 15-second protein shakes ad is tailored to your recent fitness app activity.

Advantages and Disadvantages of SSAI

SSAI involves stitching ads directly into the video stream on the server before delivery to the user’s device. This method creates a continuous stream combining content and ads, smoothing the transitions between them.

Advantages:

• Seamless Playback: By integrating ads server-side, SSAI reduces buffering and provides a more consistent viewing experience.
• Ad Blocker Resistance: Since ads are part of the content stream, they are less detectable and less likely to be blocked by ad blockers, ensuring higher ad delivery rates.

Disadvantages:

• Limited Interactivity: SSAI may not support certain interactive ad features, such as clickable overlays, limiting engagement opportunities.
• Complex Implementation: Integrating SSAI requires more sophisticated infrastructure and coordination between content and ad servers.

SSAI real-world example

You’re watching a live NBA game on a FAST channel, and a car ad flows in without a hitch, with no buffering or awkward cuts.

In summary, CSAI and SSAI each have unique strengths and limitations. Evaluating your organization’s goals, audience preferences, and technical resources is essential in selecting the most appropriate ad insertion method.

SSAI and CSAI examples use cases: Which is better?

SSAI and CSAI are two different approaches to inserting ads into video content, each with specific use cases suited to their strengths. Here are some examples of use cases for both:

SSAI Use Cases

• Live/Linear Streaming, FAST channel: SSAI is ideal for live events or linear TV streams where seamless ad insertion is crucial. It ensures viewers don’t miss important moments due to buffering or technical issues.
• OTT and Connected TV Platforms: SSAI provides a consistent experience across various devices, making it suitable for OTT services and connected TV environments.
• Ad-Block Prevention: SSAI helps bypass ad blockers by stitching ads directly into the content stream, making them indistinguishable from the main content.
• Long-Form Content: For longer videos with mid-roll ad breaks, SSAI ensures smooth transitions between content and ads, maintaining viewer engagement.

CSAI Use Cases

• Video-on-Demand (VOD) Streaming: CSAI allows for real-time ad personalization and interactive ad formats, which are well-suited for on-demand content where viewers expect more control over their experience.
• Short Pre-Roll Ads: CSAI is effective for delivering targeted, short pre-roll ads at the beginning of video content when viewers are most engaged.
• Highly Personalized Advertising: CSAI enables real-time ad decisions based on user data and behavior, making it ideal for platforms that prioritize hyper-targeted advertising.
• Interactive Ad Formats: CSAI supports more versatile ad formats, including interactive ads, allowing for greater viewer engagement.

Both SSAI and CSAI have their strengths, and the choice between them often depends on the specific requirements of the content provider, the target audience, and the advertising strategy. Some platforms may opt for a hybrid approach, leveraging the benefits of both methods to optimize their ad delivery and user experience. For example, a FAST channel like Pluto TV uses SSAI for live content but CSAI for targeted pre-rolls on demand.

The Future of Ad Insertion in the US

Ad insertion in the US is evolving fast by 2025, driven by tech advancements, privacy shifts, and consumer trends. Here’s what’s shaping the future of SSAI and CSAI:

1. CTV and OTT Growth: SSAI leads on Connected TV and OTT platforms like Netflix and Hulu, delivering seamless ads that dodge blockers across devices.
2. AI Personalization: AI powers CSAI with real-time, tailored ads, while predictive analytics boosts efficiency for both methods.
3. Privacy Focus: As cookies fade, SSAI and CSAI rely on first-party data and contextual ads to stay compliant.
4. Short-Form Video Boom: CSAI excels in personalized short ads on mobile, while SSAI ensures smooth mid-rolls in longer streams.
5. Interactive Ads: CSAI drives clickable, shoppable ads; SSAI integrates them seamlessly into CTV and AR experiences.
6. Omnichannel Delivery: SSAI unifies ad experiences across devices, while CSAI enhances cross-device targeting.

In 2025, SSAI will rule live streaming and CTV for its reliability, while CSAI shines in personalization. A hybrid approach blending both will likely define the future, balancing engagement, privacy, and scale.

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Conclusion

Selecting between SSAI vs CSAI in 2025 is not a universal decision—it depends on specific needs. For a seamless, ad-blocker-resistant experience serving millions of US viewers, SSAI is the preferred choice, particularly for live streaming and FAST channels. Conversely, for personalized, interactive ads targeting niche markets, CSAI proves highly effective, excelling in video-on-demand and precision campaigns.

ith video ad spending projected to exceed $200 billion, proficiency in these ad insertion methods is essential for maintaining a competitive edge in the US market. If your business seeks to establish an OTT linear channel with SSAI or build a FAST channel, contact OTTclouds to discuss tailored solutions and elevate your monetization potential today.