How Does VAST Work?

Read Time: 6 minutes

A few months ago we posted an article explaining how banners work. Today, I’m extending that to talk about how VAST works and what it exactly is. VAST is a type of banner, but there are some very unique features to it. If you haven’t read our first article, I recommend it to give you a good base layer.

To start: VAST is an acronym for Video Ad Serving Template and is an industry standard way of delivering video ads. It includes the actual ad (usually in multiple file formats) and the links needed to track the ads performance, delivered via a VAST tag.

An example VAST tag.

How VAST works

When AdButler generates a VAST zone tag, we’re actually giving you a direct link to the VAST banner. The tag is what you pass to your VAST video player, and is implemented based on its own documentation. Then, depending upon how you setup the player, the ad will show when a video is played.

I know it’s old school, but I like to think of the VAST tag as a tape, and the video player as a VHS player. VAST contains all the information, but you still need something to display it.

If you take the VAST zone tag and paste it into a browser instead, you’ll be directed to the VAST document, which is a standard XML file including everything a VAST ad needs. XML is a file type, like HTML or CSS.

The XML file is the trick to VAST: no matter where it comes from, whether it’s an ad exchange, a server, or a network, it’s going to look the same. Basically, when a video player says it supports VAST, you don’t have to worry about macros or JavaScript vs. HTML or any other considerations. It should just work. The only issue you may run into is different versions of VAST, but those are usually telegraphed very clearly. AdButler is VAST 2.0 certified and should work with almost all players.

What’s in the tag?

When you go to the VAST document, or when a video player tries to display the ad, AdButler picks which banner to display based on its schedule and delivers the appropriate XML file. The XML file contains a broad range of information that can be broken down into four parts.

First comes the information about the banner itself, including its title. Second, the XML contains links to the tracking events for the ads, which record when specific events happen (such as a mute or an impression). This section also includes a link to the destination, which works the same as any other banner.

The third section is a link to the video creatives. Due to the wild world of video formats, a VAST banner can contain multiple versions of the same file, varied across format, dimension, bit rate, and other properties (video is complicated). Different formats are important for VAST because some players and devices can only play certain types of videos. This is why we recommend having at least two format and two resolution variations for each VAST banner.

A player not having access to the right files may be why AdButler may record a request but not a view. It still counts as a successfully delivered banner, just one that wasn’t viewed. The last piece of the VAST tag contains any companion or static banners, as well as certain other pieces of information, like whether the ad is skippable or not.

A VAST ad can deliver more than just video, though. It can also deliver companion and overlay ads. Companion banners are similar to roadblocks, and are displayed on the same page as the video as standard display units. VAST also allows you to deliver ads to be displayed over the video player. These are called “Non-Linear” ads, while video ads are called “Linear” ads.

A proper VAST player is able to read all the information in the XML and run it accordingly, firing off events (like pause or full screen) to be recorded and displaying the best-fit creative for the device it is on.

Working With Vast

We have a video going over how to create a VAST banner, and there are numerous tools out there to help you check whether a VAST tag is configured properly. We also have a dedicated section of our help documentation on working with VAST and some best practices.

Finally, I wanted to highlight these best practices. As I said above, you should always have at least two different file types and resolutions in each banner. This helps increase how many people can see your banner. It’s also important to optimize your ad so it isn’t too big. A viewer, especially a mobile one, won’t be very happy if your ad takes a long time to load. Trying to keep your creative under one MB a minute is a good rule of thumb. You’ll also want to avoid using any special characters when naming a VAST banner or file. They can cause problems down the road with certain video players.

Besides that, working with VAST may be the simplest form of advertising. It takes care of everything for you, and if you’re working with a good video player, you shouldn’t have any problems.

Liam Workman


Liam is an account manager and blog king at SparkLit, the SaaS company behind AdButler and FourEyes. He loves rock climbing, hiking, coding, and being your friend.