How Does Video Ad Serving Work?

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  • Post last modified:January 21, 2021

How does video ad serving work and what factors make the best video ad server?

Video advertising is one of the most effective ad formats used in display advertising. Even more so, on mobile platforms as consumers are spending more time, consuming content and watching video adverts on their mobile devices.

As an advertiser, you need to understand how video ad serving works and the different types of video ad formats available.

Video ad serving works the same as ad serving, where an ad creative is ‘served’ from an ad server into multiple websites or applications. There are two types of ad servers – the advertiser ad server and the publisher ad server.

The best video ad serving platforms follow the IAB standards, using an XML specification called VAST. It allows video ads to be served into any online video player on different platforms (mobile & desktop, web & app) that supports VAST. Put bluntly, VAST allows video players and ad servers to speak the same language.

There are two types of tags that a video ad server should be able to generate, a VAST and VPAID tag. This tag is passed on to different publishers and tracking is done across them.

The difference with VPAID is that it allows ads to have more interactive features. It also allows video ad servers to track more advanced measurement, around ad viewability.

Types Of Online Video Ads

There are several types of video ads, each with their strengths and weaknesses. There is no one single best video ad format, but rather, as an advertiser, you should pick certain ad formats depending on the KPIs of your ad campaign.

We’ll briefly introduce and explain the different types of video ads.

In-Stream Video Ad

How Does Video Ad Serving Work? 1

The most common type of video ad that most are familiar with. In-stream video ads are ads that play within the video player – before, during or after a video content.

Advertisers call these ads the pre-roll, mid-roll and post-roll ads. They are also known as linear ads as they play inline with the video content.

Following the IAB standards, these ads are usually 15 to 30 seconds in length. They can be shorter but is rarely any longer than 30 seconds.

Pre-Roll Video Ad

A pre-roll video ad plays before the content. It is usually non-skippable thus making the ad attention-grabbing, but because of this, could cause a negative brand impact – if not implemented correctly.

Mid-Roll Video Ad

Mid-roll video ads are ads that play in between content. The video content gets paused when a mid-roll ad plays and continues once the ad complete. Mid-roll video ads get very low abandonment rates, as the viewer is already invested in watching the video content. However, on the downside, they are quite intrusive.

Post-Roll Video Ad

Post-roll ads are ads that play upon the end of video content. They are non-intrusive but often get higher abandonment rates, as the viewer has already reached the end of the content and has no need to stick around.


Out-Stream Video Ad

How Does Video Ad Serving Work? 2

Out-stream video ads are ads that run out of a video player or video content. It runs just like a display banner and can be served as a display banner ad between website content or in-app.

Out-stream video ads can also be made to autoplay in a muted state, upon being scrolled into view and upon tapping or mousing over, the audio turns on.

There are a few advantages to running out-stream video ads:

  1. They do not need to be constrained to video content. This means they can be served into more ad inventories, including premium placements.
  2. They are less intrusive as they do not interfere with video content.
  3. They blend within website content and encourage more engagement.

Out-stream video ads are found to have a 2.5% higher clickthrough rate compared to in-stream ads.

How Does Video Ad Serving Work? 3

Types of Ad servers

Ad servers can be broadly classified into two different types:

  • Publisher ad servers
  • Third-party ad servers

The publisher ad server will only be responsible for distributing content to the publisher’s domain.

On the other hand, third-party ad servers are equipped to deliver the ads over multiple domains. The publisher will have to make a contract with the third-party service for this. They will have full access to the third party control centre, which lets them have a tight grip on how the ads are served.

Third-Party Ad Servers vs Publisher Ad Servers

There are no hard and fast rules regarding the choice of an ad server for the publisher. It all depends on the type of business and preferences.

If you are purchasing ads only for a small number of sites, it will be better off with a limited number of publishers serving them. On the other hand, if you want a more robust approach for a broader advertising campaign, signing up with a third party server will be a great idea, you will have more control over your ads and you can also have a detailed analysis of their performance.

Before the emergence of third-party service providers, the marketers had to directly send their creatives to the publishers, which was a more time-consuming process. However, after these were invented, advertisers could target their audience more effectively.

Role of a video player in serving the ads

The video player is the most vital interface which acts as a link between the advertiser and the user.  For displaying the video ads, the player has to communicate with the ad servers and the device simultaneously.

You might have noticed that media services that stream video content through the internet like OTT devices have their own specifications. To streamline this process, VAST ad tags were introduced.

This is a universal ad serving template which allows easy synchronisation between video players and ad servers without any hassles.

Steps involved in Video Ad serving

Let us take a closer look at the dynamics of video ad serving. This is the technique by which a video ad arrives on your mobile device. 

Following are the steps in which the ad loads from the website to the view of the user.

  1. When the user opens a video player (say, for example, YouTube), a request will be immediately sent to the publisher’s server to retrieve the video ad. 
  2. The video ad server will check the target setting to determine which video ads can be shown for the specific request. It also informs the video player about when to show the ads, how to show and other tracking information. 
  3. The video ad server will send out a code to the web browser regarding how and where to display the video. To make this possible, the player must support HTML5 video and VAST tags.
  4. Upon receiving the content, the video player will immediately request the retrieval of the video ad from the publisher’s ad server. The server of the publisher will determine which video to show programmatically and send back an appropriate ad markup.
  5. Once the player receives an ad markup, an ad retrieval request will be sent to the server of the advertiser. Upon receiving the request, the ad server marks an impression and returns a link which enables the video player to play the required video content.
  6. Video ad can be shown before the actual video content (pre-roll), in the middle of the actual content (mid-roll) or after the actual content (post-roll)

The Video ad server will be responsible for distributing the ad, as in most cases the ad will be hosted there.

Video Ad Serving Template (VAST)

VAST is a video ad serving template by IAB. There are multiple vast versions with each one bringing new improvements. Vast 1.0 was the initial version which is now depreciated. VAST 2 and 3 are still being used and VAST 4.2 is the latest one in the picture. While the original VAST versions are still being used by some advertisers, its recent version VAST 4.2 brings forth new solutions in the world of video advertising. These include the ease of measurement and verification and improved interactivity. 

These VAST updates have streamlined the ad delivery process and put an end to the ad frauds in the online advertising world. 

VAST 4.2 also ended VPAID which was a format that offered limited transparency and was associated with many negatives like poor user experience, trust issues, etc. 

Learn more about these formats with our article on “What is VAST and VPAID and why is it important?

How To Choose The Best Video Ad Server for Your Campaigns

Ad serving is actually pretty complex. It all depends on the type of ads  (display, interactive or video), the ad platform (desktop, mobile phone, tablet, etc.) and whether the ad is served through a programmatic platform or through direct buys.

Third-party video ad servers simplify this process, acting as a platform where you simply upload video files and it takes care of the conversion, size compression, and platform compatibility.

Tracking and reporting capability are also important features a video ad server must have. Tracking functions are done with a VAST Wrapper, whereby data points from interactions, impressions, viewability, and clicks on the ad are recorded and reported on the video ad server.

A video ad server usually tracks:

  1. Video play measurement – Start rate, video percentile play, completion rate, etc.
  2. Interaction events – Mute, un-mute, resume, rewind, fullscreen, etc.
  3. Ad viewability
  4. Ad block tracking

MobileAds is a mobile video advertising platform with detailed analytics. Should you need more information about Video Ad Serving, reach out by email us @ [email protected] now!


Alvin is the Founder and CEO of He is a go-getter, and adventurous guy who believes in working smart to gain success in his business ventures and in life. He also founded and

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