Server-Side Ad Insertion (SSAI)

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Server-Side Ad Insertion (SSAI) comes under different names, and is also referred to as Dynamic Ad Insertion (DAI) or Ad Stitching. It has great opportunities for publishers to win back lost revenue due to ad blockers.

What is Server-Side Ad Insertion?

Server-Side Ad Insertion is a technology in the realm of video advertising to seamlessly integrate ads into the main video content. Contrary to Client-Side Ad Insertion (CSAI), where the VAST player pauses the main video to play the ad, SSAI delivers a single stream to the player with the ad already integrated into the main video content. The ad will become part of the content, just like in a tv-stream.

Server-Side Ad Insertion (SSAI)
AdGlare splits the content video, inserts the ad and transcodes the stream into a new single MP4 file.

SSAI has 3 major advantages

  • It circumvents Ad Blockers
    Since ads become a part of the video content itself, ad blockers are unable to block the ad as they can't differentiate between the main content and the advertisement. A simple and effective solution to win back lost revenue.
  • No more buffering
    Latency is greatly improved here since the player doesn't have to load video assets from other locations. Think about DNS lookups, HTTPS handshakes, network latency, etc. The player loads a single file, usually from a CDN node close to the user's geographical location, and buffers it right from the start. This will greatly improve the overall user experience.
  • It solves the issue of non-compatibility
    Not all browsers are able to play video ads encoded in a certain way. This can lead to missed opportunities in case the client's browser is technically not able to play the ad. SSAI makes sure that the ads are transcoded in the same format as the content video. If the device can play the video, it can play the ad.

Can SSAI win the battle against ad blockers?

Yes. At least for video content. Ad blockers scan outgoing HTTP requests and block them if the ad server domain is found on their blacklist. This allows ad blockers to prevent ads from loading while publisher content gets through. With server-side ad insertion, the whole video including the ad originates from the publisher domain, leaving ad blockers in the dark.

Then why are not all publishers using SSAI?

Although SSAI exists for a while now, adoption rate has been low. Stitching the ad into the video stream has a few hurdles and challenges to overcome. The technology largely relies on HLS (HTTP Live Streaming) which is not supported by all browsers yet. At the time of writing (June 2018), about 56.3% of all internet users are able to play HLS video. This streaming technology was mainly developed for mobile browsers, and consequently, Chrome on desktops don't support it yet. But things may have changed by the time you read this article. You can check HTTP Live Streaming support here.

As a solution, the ad stitching server can re-encode the complete video including the ads - a method called hard stitching. The resulting MP4 file can be played by virtually all HTML5 video players today, and it can be cached by a CDN. The disadvantage of this approach however is that each combination of content video and ad has to be generated before the MP4 file can be served. Transcoding takes time. Moreover, all video ads have to be downloaded from the advertiser's CDN, which requires a large amount of disk storage.

Another reason why publishers are reluctant to use SSAI is the fact that a considerable amount of VAST ads are VPAID, created using JavaScript, CSS and/or HTML5. Since it's impossible to stitch such ads into a video stream, publishers are more or less "forced" to use traditional client-side ad insertion.

Geotargeting and Unique Ads

SSAI allows for targeting just like any other ad format. The ad server's decisioning engines return a video ad based on a set of targeting rules, just like with VAST. The ad stitching server can even apply a GDPR-compliant frequency cap at user level, since all ads will come from this single source.

Impression and click tracking in SSAI

Tracking in SSAI is commonly done using client-side methods, pretty much just like traditional display ads are sending impression, click and conversion data back to the ad server. To avoid ad blockers in this part of the stack, you can consider to white-label your ad server and send tracking data via your own subdomain to your ad server.

Another option is to let the ad-stitching server handle all tracking. This may pose a problem in the sense that all requests are coming from a single IP address, which may look like fraudulent traffic. To overcome this issue, the ad-stitching server should set the X-Forwarded-For header to include the client's IP address. The ad server that processes tracking data should be able to read this header in order to log impressions correctly.

Enabling Server-Side Ad Insertion in AdGlare

AdGlare offers Dynamic Ad Insertion as part of our ad server solution. As a publisher, you just have to include the URL of your main video content in the ad tag. AdGlare's engines will then pull an eligible ad, stitch it into your content and play it as a single MP4. One player, one stream. The engines will create a custom-built HTML5 video player that handles the tracking of ads while the single MP4 video is played.

Please contact your personal account manager to discuss details and pricing, as SSAI has to be enabled for your account separately.


Server-side Ad Insertion is an excellent way to circumvent ad blockers and to win back lost revenue on video ads in case you're a publisher. The technology comes with great solutions regarding buffering, latency, video codecs and the overall user experience. Although there are a few technical hurdles to overcome if you're taking this route, the advantages may well pay off.

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