What is Server-Side Ad Insertion?

Digital publishers have multiple options for monetizing their content. The fastest growing category of ad spending is video.

The Interactive Advertising Bureau (IAB) reports that ads in video content rose 49% in 2021 and are expected to grow again by another 26% in 2022. Video on demand (VOD), Connected TV (CTV), and over-the-top (OTT) video are expected to account for more than $50 billion in ad spending in 2022.

The two main ways to insert ads into video content are server-side ad insertion (SSAI) and client-side ad insertion (CSAI). The main difference between the two focuses on how ad breaks occur within streaming content. For publishers, which type of delivery system you use when choosing programmatic platforms can make a difference in monetization.

It’s worth noting that both SSAI and CSAI are different from utilizing embedded video ads as part of your programmatic monetization strategy.

In this article, we’ll discuss the pros and cons of each method, along with use cases for driving website revenue.

What is Server-Side Ad Insertion (SSAI)?

Server-side ad insertion is the process of inserting ads into video content. Generally, SSAI appears in long-form video content and allows for a seamless transition between content and ads — and then back to the content again. Ads serve instantly without buffering to provide streaming users the same type of user experience they have watching television.

Unlike television, however, SSAI allows for dynamic ad insertion (DAI) with no latency. An ad server can deliver dynamic content based on device and bandwidth throughout a video stream using an AdTech process called ad stitching. Depending on the user’s bandwidth and device, SSAI serves ads at the best possible bit rate and format.

Server-side ad insertion is an effective way to beat ad blockers. Because it stitches together video content and ads into a single stream, the video ads you serve are virtually undetectable by ad blocking technology.

How Does SSAI Work?

One of the big advantages of SSAI for viewers of video streams is that the process of delivering ads is seamless and flows naturally into the stream without disruption. Viewers don’t notice the ad calls that the server handles — not the user (client). Here’s a breakdown of how SSAI tech works when someone is watching a video during an over-the-top (OTT), CTV, or video on demand (VOD) stream:

  1. When the viewer launches the stream, the video player sends a request to the SSAI provider or vendor. It includes information such as device, internet service provider, bandwidth availability, and location.
  2. An ad decision server produces what’s called a manifest. The manifest is like a playlist that includes video segment durations, advertisements for streaming, and beacons to activate ad calls.
  3. The content delivery network (CDN) will enable the playlist that provides the stream to the user using the manifest. Ads are sent not to the user but to the CDN, which transcodes and stitches them into the program stream.
  4. The video player automatically sends the ad request to the ad decision server whenever playback hits these beacons, and the CDN initiates an ad break within the stream.
  5. The ad decision server tracks the playback to report that ads are active during the stream.

When Should You Use SSAI?

SSAI supports a seamless viewing experience with little to no buffering. So, if avoiding buffering is important, SSAI is your best choice for ad delivery for online videos. It is especially effective when you broadcast live events or live streaming via CTV or OTT to provide an optimal viewing experience.

This seamless user experience from your SSAI vendor and content delivery network (CDN) allows you to optimize DAI for monetization.

What is Client-Side Ad Insertion (CSAI)?

Client-side ad insertion lets you deliver a more customized ad experience for the end user. Ads can be hyper-targeted to an individual user based on cookies and behavior. Ad serving networks can provide content relevant to either the program being streamed or the user viewing the program. This allows advertisers to target groups of users that display the same interests or, in the case of Connected TV, deliver one-to-one advertisements targeted to specific known IP addresses. At the same time,

However, ads are only delivered after an ad request has been initiated, which can lead to slight delays in delivery.

How Does CSAI Work?

Let’s take a look at how CSAI works in action so you can see some of the differences between SSAI and CSAI. Here are the steps involved in the workflow to deliver video ads by inserting them on the client side rather than in the stream.

  1. Within the video stream, ad markets are inserted, which tell the video player when it’s time to take a break and switch to an advertisement.
  2. When the user’s video player reaches a marker within a stream, it pauses and initiates an ad request to the ad server.
  3. The ad server gets the ad call and delivers the best-fit ad based on user interests and activity.
  4. Once the ad completes, the stream’s playback begins again.

The software developer kit (SDK) embedded in the video player is what manages the tracking beacons and initiates the ad request. Because there is a delay between the time it takes the SDK to initiate the ad call and the ad server to respond, there can be similar delays in delivery. This can add pauses, latency, and buffering as ads begin to serve or programs resume after ad plays are complete.

HTTP live streaming (HLS) can adapt to the video player’s changing bit rates and bandwidth. Advertisers must make sure to provide ads at different bit rates and quality levels to optimize viewing on the client side.

When Should You Use CSAI?

Client-side ad insertion is the best choice when you need to deliver ads targeted to specific users based on interest. If you want to run interactive ads and track specific user interactions, CSAI may also be a good choice.

Advertisers must weigh the advantages of user targeting in video streams against the potential negative impact on the viewing experience from buffering and delays. Publishers will need to decide which method is the best for monetization of their video assets.

The Differences Between SSAI and CSAI

The main difference between SSAI and CSAI is how they deliver ads. CSIA makes calls from the video player to an ad server that delivers the ad. SSAI does not require an ad call, instead inserting the ad directly into the media stream.

There are pros and cons to each method.

Pros and Cons of SSAI

Server-side ad insertion has significant advantages. SSAI benefits include:

  • It provides a better user experience. There are no obvious transitions, such as blank screens, loading pages, or pausing during CTV or OTT streams.
  • Using adaptive bit rate streaming to adapt to user internet bandwidth and device for optimal viewing.
  • Removing latency and buffering issues for a consistent and seamless experience.
  • Bypassing detection by ad blockers, so you don’t lose monetization and ad revenue options.
  • Providing a consistent playback and reliable stream that improves engagement.
  • Serving relevant ads with respect to the context within the video content.

There are also some disadvantages of using SSAI.

  • Because the ad server is responsible for serving (stitching) the ad rather than the viewer’s device, this creates challenges in measurement.
  • Third-party verification vendors are unable to access client-side data, which can limit the effectiveness of ad targeting.
  • There have been several incidents of fraudulent traffic generated by unscrupulous actors. In one case, a botnet was able to generate more than three million fake impressions a day. Fraudsters also set up counterfeit SSAI servers to “ manufacture” inventory that didn’t exist.

Pros and Cons of CSAI

Like SSAI, there are pros and cons to client-side ad insertion. The biggest benefits include the ability to:

  • Serve rich, dynamic ads that include interactive elements, such as surveys, click-throughs, and overlays.
  • Produce detailed tracking of ad plays and interactions.
  • Deliver highly-personalized ads using client-side targeting and behavior for greater engagement.

The disadvantages of CSAI include:

  • Because ad decisions aren’t made until there is a call to the ad server, users must wait for ads to be delivered. This introduces latency into the workflow and can lead to an uneven streaming experience.
  • With a different server streaming the ad, users must wait while ads buffer.
  • There can often be a significant quality difference between content and ads, you can have varying bitrates and resolutions.
  • API calls to ad servers are often caught by ad blockers, which can then block the playback of the ads in OTT or VOD streams.

With both SSAI and CSAI, competing ad technologies are also being used. This can add to the complexity and incompatibility of measurement. Trade groups such as the Internet Advertising Bureau are working to create common header information to standardize processes and optimize reporting. For example, IAB’s Video Ad Serving Template (VAST) is a format to standardize communication between video players and video or ad servers. It works to coordinate traffic across different types of publishing platforms.


The main difference between server-side ad insertion and client-side ad insertion lies in the initiation and serving of ad requests. SSAI handles it all on the server side, requesting and inserting ads into a video stream and delivering it as one continuous stream. CSAI initiates the ad call on the user device, pauses delivery, and lets the ad server take control until the ad concludes. It then restarts the stream.

CSAI provides more granular targeting but may also result in delays and buffering. SSAI creates a more seamless video stream but does not allow for hyper-targeting.

There are pros and cons to each method of delivering ads and monetizing your video on demand. Contact the digital advertising experts at Newor Media to discuss your ad insertion options.

Want to see how much money your website could be earning with ads? Check out Newor Media’s Earnings Calculator tool.

Bridget George

Senior Account Manager, Publisher Development: Newor Media

Bridget is a dynamic business development and account manager. She has been in the ad tech industry for over 7 years and is known for her ability to drive innovative solutions and foster strategic growth. Passionate about her work, she excels in managing key accounts and ensuring client satisfaction.