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The Encyclopedia of Video Ad Serving: What Video Ad Tags Are and Why You Should Care

Nov 23, 202315 min read
Stepan Krokhmal
Stepan Krokhmal, AdTech Writer

Video is the dish best served warm…

You don’t need bulky statistics to know about the success of video advertising. A little reminder: an online video ad spend worldwide accounts for 74.6 billion USD.

Whether it’s because video ads are the perfect format in the age of ad personalization or our unga-bunga brains process visuals almost 60,000 times faster than text, 91% of marketers are already using videos in their campaigns.

But we’re not here to talk about video advertising alone(maybe just a little bit). “How does video ad serving work?” is a more interesting question to put some light on.

Today, we dig into the ins and outs of video ad serving; you’ll discover how video ads work, which ad tags serve what purpose, and how to serve high-performing video ads yourself.

Meet VAST, VPAID, VMAP, MRAID, SIMID, and OMID. Let’s roll!

How Does Video Ad Serving Work?

*All video ads are served with the help of video ad tags. Before we move on to them, it’s important to understand the differences in terms so you don’t get confused further on.

Since the first-ever video ad was broadcast on WNBT in 1941, video advertising has come a long way. Just like their TV ancestors, video ads can’t exist without the main content, but the ads themselves are quite different.

How Are Video Ads Served?

From a technical standpoint, video ads are served in two ways:

  • Instream

According to the latest IAB guidelines, instream videos are ads served inside the main video player and played with the sound on by default. Like on TV💀 or YouTube, the main player stops when an instream ad launches.

  • Outstream

The video ads that live outside the main video player are called outstream video ads. They don’t require an HTML5 video player and run on mute.

Which one’s better? Well, they serve different purposes, but for the most curious – we’ve already touched upon instream vs. outstream ads.

What Video Ad Types Are There?

One more thing before we move on. Ads can also be divided by types according to how they interact with the main content.

  • Linear video ads

Linear video ads run in the same video player as the main content. All linear ads are instream and can be played before (pre-roll), during (mid-roll), and after (post-roll) the video content.

  • Nonlinear video ads

Non-linear video ads can be both instream and outstream. Nonlinear instream ads run inside the video content, but they can either overlay it (like playing in the bottom quarter) or just run at the same time as the video.

The outstream non-linear video ads run just as you’d imagine: outside main video content on mute.

What Is VAST?

*We’ll call VAST, VPAID, and others – tags just for the ease of readability.

Video Ad Serving Template (VAST) is responsible for 90% of the ads you’ll see online. This IAB template, launched in 2008, is the basis of modern video ad delivery.

Technically, VAST is not an ad tag; VAST is an XML schema that structures different ad tags that, in turn, serve ads to video players. VAST contains important metadata about an ad; it transfers this information from the ad server to the video player.

What’s this metadata? VAST consists of:

  • Media file with the ad creative;
  • Tracking elements that map to video events (impression tracker);
  • Ad format (out-in-stream/pre-mid-post-roll, overlay/non-overlay, etc.).

What are the examples of VAST? In raw code, the VAST tag looks something like this:

the examples of VAST video ad tag

With that out of the way, let’s discuss how these elements work together.

How do VAST ads work?

The way video tags work is similar at its core; we’ll explain the basics with VAST.

Step # 1. Request. The video player calls an ad server for an ad.

Step # 2. Response. The ad server gets the request and responds with a media file and a tracking URL.

Step # 3. Tracking. Once the main video triggers, the video player launches the impression tracking URL.

how VAST ad tags work

What Are the Benefits of VAST?

As we’ve mentioned before, most online video ads are served through VAST, and that can be explained by its three core benefits:

  • Seamless and quick communication between ad tech elements;
  • A universal tool that eliminates the need for custom video ad players, thus saving resources;
  • Simplicity of code reduces the risks of playback errors;

What Are the Versions of the VAST Tag?

Each version of the VAST tag builds and improves upon the formula. We, however, don’t really know why anyone would want a full changelog, but since it’s a really popular question, here you go:

VAST video ad tag versions

Over the years, VAST has significantly improved, but despite all the updates, it was never intended to run more complex video ads. The first attempt to solve this problem was VPAID.

What is VPAID?

Video Player Ad Interface Definition (VPAID) is a block of code that allows video players and video ad units to interact. Currently, there are two versions of VPAID with VPAID 2.0 support and ad resizing.

How Does VPAID work?

A quick glance at the steps below will seem oddly familiar if you’ve read carefully. That’s right, VPAID operates similarly to VAST, but for a better understanding, let’s glide upon the details.

Step # 1. Request. The video player sends an ad request to the ad server.

Step # 2. Response. The ad server responds with a VAST XML that contains the VPAID.exe ad unit.

Step # 3. Communication. The video player and VPAID ad unit communicate by exchanging info on ad unit properties and video events. In the meantime, the user sees the ad.

Step # 4. Impression Tracking. The ad unit and the video player send the impression data to their ad servers.

how does VPAID work

VAST vs. VPAID. How to Distinguish VAST from VPAID?

What is the difference between VAST and VPAID? VPAID came as a more advanced and complex version of VAST that allowed serving interactive ads and rich media + tracking how the users interact with them. But that hardly explains anything, so let’s dig deeper.

Okay, big-brain time.

Difference 1. Purpose

VAST establishes communication between the ad server and video player, while VPAID connects the video player and video ad units.

That means that the main mission of VAST is to ensure that video ads run in the video player just how the ad server tells them to. The main objective of VPAID is to build upon this foundation and make sure that more complex ads can interact with the video player.

Difference 2. Form

That’s why VPAID is an executable code that can be implemented in JavaScript or ActionScript.

However, if publishers want to serve VPAID ads, they must ensure their video player supports VPAID API.

VPAID can work independently, but that would be like making a pickup when you can order a delivery. Thus, VPAID is usually served in a VAST template, so you get the simplicity and stability of VAST with the cool features of VPAID.

Difference 3. Functionality

So, what are these features that justify the VPAID hassle? The most notable are:

  • Auto-resume of content after the ad is played;
  • Support of interactive elements;
  • Override when the ad takes too long to load (stops the ad, resumes the content);
  • Resizing of the ad.

Both VPAID and VAST serve single video ads, but what if you need multiple ads? Let’s talk about VMAP.

What is VMAP?

Video Multiple Ad Playlist (VMAP) is an XML template that allows playing multiple ads during the video. Yup, nothing too complicated about it.

VMAP is used in combination with VAST. Think about VMAP as the timecode feature on YouTube. During a video, VMAP tells the player when each of the multiple ads has to launch.

It doesn’t specify which ad has to play; that’s the job of an ad server.

Why Is VMAP Used?

VMAP is a tool designed to solve really specific problems. Let’s say you’re an advertiser who wants to insert an ad into a YouTube video. You don’t have much control over the timestamps of ads; neither does the content publisher.

VMAP allows to configure the number of ads, ad breaks, and their availability. Needless to say, how useful it is.

However, VMAP doesn’t make much sense if you have direct access to the video player and every piece of content that it could show. But to be honest, that’s rarely the case for advertisers.

The VMAP should look something like this:

how does VMAP work


This article is getting really long, but we still have three more video ad tags to cover. Don’t worry; we’ll be as brief and efficient as possible.

What Is MRAID? What Are the Benefits of MRAID?

Mobile Rich Media Ad Interface Dimensions (MRAID) is IAB’s API created to serve rich media ads on mobile platforms.

Java, Swift, Kotlin, Objective-C, and hundreds of SDKs — the diversity of stuff that has to be supported makes serving video ads on mobiles one huge hot mess, and MRAID aims to fix that.

The IAB calls it a “write once, run anywhere” standard; with MRAID, advertisers can serve ads on all mobile devices without caring too much about errors and bad execution.

We’d love to talk even more about this unsung hero, but for the sake of keeping it short, here are three things you have to keep in mind about MRAID:

  • Currently, there are three versions of MRAID, with MRAID 3. 0 being the latest. What’s cool is that all these are backward compatible + the latest iteration supports ad resize, expenditure, and even native device functions (like device orientation);
  • Not all mobile rich media ads run with MRAID. Some providers develop their own framework instead.
  • MRAID 3.0 supports some of the VPAID events related to reporting.

Now that you know of MRAID, let’s move to more controversial stuff.

What’s Wrong with VPAID?

Remember everything good we told you about VPAID? Well, the standard has a lot to be desired.

Firstly, VPAID was designed to serve interactive media as a first priority and track its performance as a second. As a result, publishers often complained about the high rendering failure rate. Some sources claim that the error rate reaches up to 30%.

If a video fails to render — publishers don’t get paid for impressions which definitely sucks.

Secondly, VPAID is vulnerable to exploits and data leaks. That mostly relates to VPAID creatives served through older versions of VAST, but as you might’ve noticed, ad businesses are really conservative in how they operate.

What is SIMID? What Is OMID? Are they the same thing as VPAID?

IAB is fully aware of all these issues; that’s why VPAID is no longer updated. The successors to VPAID are SIMID and OMID.

So, what is SIMID?

Secure Interactive Media Interface Definition (VPAID) is basically VPAID, but more secure and more accessible. SIMID supports mobile, OTT, and even SSAI.

In fact, the list of changes is even broader. SIMID has:

  • Better playback stability;
  • Better error handling;
  • Better UX(at least IAB states that);
  • Better data security;
  • More control for publishers.

How does it do this? SIMID separates the interactive part of the ad from the media asset the user sees. In short, it gives playback control to the video player itself rather than being the boss of ad placement (thus giving publishers more freedom).


What about OMID?

While SIMID covers the publisher’s side, Open Measurement Interface Definition (OMID) is responsible for better transparency for advertisers.

OMID is an open-source API. Its main purpose is to simplify how advertisers view and verify ads. How does it improve what was in VPAID?

Firstly, with VPAID, advertisers needed multiple SDKs to verify ads; now they have one.

Secondly, with VPAID, placed ads required access to the whole page rather than just a video player. This, naturally, increased the security risks.

What’s with the deprecation of VPAID?

SIMID and OMID, used in tandem, completely outmatch VPAID. They make the advertiser-publisher relationship more safe and transparent while providing them with more diverse and stable ad placement.

IAB even has special SDKs for OMID to improve adoption rates, but that hardly makes the difference.

Yeah, the global market doesn’t really like changes, even if they are for the better. That’s not catastrophic, we all have old habits. But just like “Smoking kills” on the front of your vape package, we hope to increase your awareness of positive change 😉

How to Create Vast Tags with Epom Ad Server

Okay, you’re probably tired already, but we still have one thing unsettled. Let’s extract a VAST tag with four easy steps:

  1. Create a Video Banner from the “Advertiser” tab:
video banner creation
  1. Upload a Creative
creative uploading for VAST completing creative information
  1. Link it to the Video Placement from the “Publisher” tab.
video placement link from publisher tab video placement editing
  1. Copy the tag.
video ad tag copying
  1. Extra. Epom Ad Server supports VAST events tracking. Select the items you need in the Vast Events pane to enable this feature.
VAST events tracking

Wrapping Up

The basic knowledge of video ad tags will help you understand how to mark all the spots in your campaign plan. Yeah, that’s a lot of information, but trust us, it’ll get in handy once you start improving your video campaigns.

By the way, you can start doing it today; the Epom ad server supports a wide variety of ad formats, video ad tags included.

Use the latest versions of VAST with the Epom ad server!

Serve Video Ads like a Pro

FAQ Section

  • What is the difference between VAST tag and an impression tracker?

    An impression tracker is part of the metadata that VAST contains. So it’s like asking, “what is the difference between cheese pizza and cheese?”

  • What is meant by “failed to load the VPAID ad?”

    Issues with VPAID are often associated with VPAID implementation rather than SDKs. So in case you get this error, reach out to the creative provider.

  • Which three creative types are allowed when using VPAID creatives?

    The latest version of VPAID allows serving full-screen expanding, interstitial, and HTML5 non-linear creative types.

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