CSAI vs SSAI: What are the differences?


When considering a monetisation strategy, it makes sense to carefully weigh your options. You may already have heard about Client-Side and Server-Side Ad Insertion. But what are they, and where does each strategy shine?

Client-Side Ad Insertion

In a CSAI-flow, advertisements are managed and added on the end-user’s device. From a delivery point-of-view, content and ads are separated; the player plays content and advertisements independent of each other. The player will switch between the two as needed. Client-Side Ad Insertion is specified via the IAB (Interactive Advertising Bureau) standards:

  • VAST (ad metadata)
  • VMAP (ad timing)
  • VPAID/SIMID (interactive ads) and
  • OMID (viewability measurements)

A compliant player supports all ad solutions that adhere to these standards, making it easier to switch to another provider. CSAI-systems with a different flow can then be added on an individual basis. Alternative implementations, for instance Google IMA, can also be added in parallel.


Server-Side Ad Insertion

In an SSAI-flow, advertisements are directly stitched to the streaming manifest on the server side at the last moment. The content and advertisements are closer related to each other, allowing smoother playback and transitions. This way of working is comparable with traditional linear television. The main difference between broadcast advertising and SSAI is that the latter allows advertisements to be targeted towards individual end-users.


Server-Side Ad Insertion is only partly standardised. SCTE-35 markers are a popular technique to signal the encoder and packager where ads are allowed to be inserted. It was, however, never intended to be used towards streaming clients. As a result, SCTE-35 is often only used to inform SSAI providers where ads should be placed. How they place those ads, and how they provide the relevant metadata for tracking ad progress, is not standardised. This metadata is needed to build a CSAI-like experience: showing a click-through, giving an indication about duration and current time. Some common strategies include:

  • Fetching metadata from the SSAI provider’s backend
  • Adding timed cues via ID3/EMSG
  • Parsing custom tags from the streaming manifest
  • Integrating with a proprietary library

A video-player pre-integrated with multiple SSAI vendors improves the interoperability between all of them.

Can I earn more with CSAI or SSAI?

It depends.

Generally speaking, in conclusion, SSAI may be more expensive than CSAI, but also results in much more ad impressions. Ad blockers may be less effective against this type of advertising.. This is due to the tighter integration between content and advertisements and the increased complexity overall. These additional costs have to be subtracted from the Cost Per Mille (CPM) pay-out. The higher cost of SSAI, however, can be easily countered by the fact that it provides a much higher fill-rate.


Ad blockers have primarily been optimised to block CSAI ads,

but are not sophisticated enough to detect SSAI ads and block them.

CSAI ads are not always able to play due to ad blockers, errors happening on the client side, time outs for loading an ad, errors in VPAID ads et cetera. In practice, ad providers typically only promise a fill-rate ranging between 25 and 55%. In the case of SSAI, ad-blockers may block the integration libraries or the origin of the ad provider, but in that case the end-user would not be able to watch the content in the first place.

In our next articles we are going to discuss the technical aspects to consider and which approach is the most effective based on your use case. Subscribe to our insights so you don’t miss it. You can also download the complete version of this topic in our “CSAI vs SSAI: Best Bang For Your Buck” guide here.

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