What Is VAST? Video Ad Serving Basics and SIMID Role

VAST is a universal XML schema for serving ads to digital video players. That is how the IAB Tech Lab describes it, and the same page says the schema also describes the video player behavior expected when VAST-formatted ad responses are executed. If you buy video ads for a small business or run a site with video content, the practical value of knowing VAST is that you can ask a publisher the right three questions: which version, which interactive standard, and which measurement route.

Example scenario: A delicatessen that sells cured meats, cheeses and gift hampers wants a short video in front of recipe clips on a food blog. The agency asks for the blog's ad tag. The blog's developer asks which VAST version the tag follows. The shop owner just wants the video to play. Three questions connect those worlds.

Asking in the right order

The questions depend on each other, so the order helps. Version and addenda come first, because the interactive layer is delivered through VAST 4.x. Interactive support comes second, because it decides what the creative team builds. The measurement route comes third, because it decides how the result is judged. The test run comes last and closes the loop.

1. Get the declared VAST version and addenda in writing.
2. Ask about SIMID support and version if the video has a tappable layer.
3. Settle the measurement and verification route, including Open Measurement.
4. Run a small test on the real player and write the result in the log.
5. Confirm that no new interactive creative depends on VPAID before the full launch.

For a small advertiser this sequence fits into a working day. What matters is that each answer is recorded and each missing answer is marked as open. When an answer does not arrive, go back to the specification or ask the publisher again rather than assuming.

A short glossary of the abbreviations

Video ad conversations pile up abbreviations quickly. This table keeps to what the IAB Tech Lab pages say. Where a page only names a term, the table says so rather than supplying a definition.

The empty cells are deliberate. The page lists VMAP as a link and does not describe it. If you bring a term like that into a vendor call, take its definition from the specification itself and write it down.

How the IAB Tech Lab defines VAST

On the VAST page of the IAB Tech Lab (Opens in a new tab), the About VAST section calls it a universal XML schema for serving ads to digital video players. The page says VAST opens up the in-stream digital video advertising marketplace and reduces expensive technical barriers, which in turn encourages advertisers to increase video ad spend. The page was last updated on July 18, 2024.

Two points follow from that definition. VAST is not a video format or a codec. It is a description of an ad that a player can execute. And because it also describes expected player behavior, the schema is read by both sides, the party that serves the ad response and the party that builds the player. Practical suggestion: when a publisher says the player supports VAST, ask which version and which addenda, because the page shows that the answer is not a single yes or no.

Ad server configuration, tracking set-up and reporting sit outside the VAST page, so those questions need the specification documents on GitHub or the vendor's own documentation, which the page links for the 4.x, 3.x and 2.x lines.

The VAST version list, entry by entry

The text lists versions and addenda. It does not label any of them as the current version. The latest core version it lists is VAST 4.3 from December 2022. Two addenda come after it in the list: VAST Addendum for attribution reporting from July 2023, and VAST Addendum for CTV 2024 from July 2024.

The table follows the page as published. For VAST 4.1 the page gives two dates: the timeline says August 2017 and the prose says November 2018, and the page does not reconcile them. The same text also notes that ACIF and CTV Ad Portfolio support appear in VAST 4.x and, through the addendum, have been added to earlier versions. Specifications change over time, so check the current IAB Tech Lab page before you put a version number in a contract.

From 4.0 to 4.2: what each release added

Version 4.0: media apart from code

The source describes VAST 4.0 as focused on delivering video ads across many devices and screen sizes. It names the separation of media files from verification and interactive code, and a mezzanine file for server-side ad insertion, among the goals. For a buyer, the separation of media from verification and interactive code is the idea that returns later in SIMID.

Version 4.1: verification and audio

VAST 4.1 is described as updates for improved ad verification, ad creative measurement, server-side ad insertion and integration of audio advertising. It also mentions support for ad requests and integration with DAAST for audio ads. Its entry says ad verification is done with Open Measurement, which is the link between VAST and the OMID work.

Version 4.2: SIMID arrives

VAST 4.2 brings SIMID support, which the page describes as the replacement for VPAID for interactive use cases, along with a few minor updates. For anyone still holding older interactive templates, this is the version entry to read first, because it ties the interactive layer to the successor of VPAID.

VPAID to SIMID: the reason for the swap

The VAST page lists the Video Player-Ad Interface Definition as deprecated and replaced with SIMID. On the SIMID page (Opens in a new tab), the Digital Video Technical Working Group is described as replacing VPAID with more focused standards. The focus is a split of jobs. OMID handles measurement and verification. SIMID handles interactivity.

The sandbox idea

The SIMID text describes the standard as a container that enables communication between the player and any ad creative. The ad is contained so that none of its code can access the player or the environment where the player is executed. Ads can ask the player to perform certain operations in response to user interactions. For technical details, differences from VPAID and sample code, readers are sent to the SIMID GitHub repository.

Two deliverables, one VAST response

A core principle on the page is separating the interactive layer from the media asset. Both are delivered through VAST 4.x. According to the source, SIMID was built to support mobile, SSAI and OTT devices. Practical suggestion: read this as a reason to treat the video file and the interactive overlay as two deliverables that can be tested separately.

SIMID 1.2 in detail

The latest version on the page is SIMID 1.2, and the page was last updated on January 3, 2024. Version 1.2 supports responsive ads by signaling -1 to report an unknown size, and it requires session IDs to be cryptographically secure. The same text also provides instructions for L-shaped ad space, also called squeeze-backs, which SIMID always supported. Deep links that open an app or an app store require additional setup, which the page explains in general terms. A related headline on the page says SIMID 1.1 added support for nonlinear ads.

Platform and stream coverage

Per the SIMID page, the standard was designed to enable better cross-platform support by supporting mobile, SSAI and OTT devices, and that it also supports server-side ad insertion and live streaming. It adds that a main tenet of SIMID is the separation of the interactive layer from the media asset, with both delivered by VAST 4.x, so publishers keep control of their streams. For a booking, that means the interactive layer is something the publisher can accept or decline on its own terms without touching the media file.

Practical suggestion: which of these a particular publisher supports is for that publisher to say. Treat each row as an open question until the publisher answers in writing, and keep the reply with the booking.

Four standards side by side

Four names appear together in IAB Tech Lab material on video ads: VAST, VPAID, SIMID and OMID. They are easier to keep apart when you list the job each one does according to the pages.

One delicatessen, three campaign types

The same delicatessen could run three video campaigns, and each one leans on a different standard. Example scenario: the first is a plain brand video, the second adds a tappable hamper overlay, and the third targets connected TV screens.

Campaign one: plain brand video

With no interactive layer, SIMID drops to the background. The questions that matter are the VAST version and the measurement route. A short test run on the publisher's real player clears up more doubt than a long email thread, and the video length and file weight are checked against the player's limits separately.

Campaign two: tappable overlay

An overlay that responds to taps brings SIMID in. The source describes a container in which ad code cannot reach the player or its environment and asks the player to perform operations for the ad. Ask the publisher whether SIMID is supported and which version. If the overlay template was built on VPAID, plan the move to SIMID, since VPAID is listed as deprecated.

Campaign three: connected TV

The July 2024 addendum adds higher-resolution creative for larger screens, icons for DSA and ACIF support. Ask whether the player or the platform supports the addendum. The 4.3 entry points to the addendum for ad creative support, so the version number does not settle the matter alone.

The hamper overlay video: questions for the publisher

Example scenario: The delicatessen's video is fifteen seconds long and ends on a tappable overlay that says Order a hamper. The agency needs to prepare two things, the media file and the overlay, and the blog needs to be able to play both. The three questions come straight from the standards table.

1. Which VAST version and addenda does the player support? Ask for the answer in writing, with the version numbers.
2. Does the player support SIMID for the tappable overlay, and which SIMID version? If the overlay was built on VPAID, plan the move to SIMID, since VPAID is listed as deprecated.
3. How are measurement and verification handled? Ask whether the player supports Open Measurement.

The three questions have separate answers. A player can follow a recent VAST version and still lack SIMID support, because the page treats the interactive layer as a separate concern delivered through VAST 4.x. In the same way, SIMID support says nothing about measurement, which belongs to OMID.

If the shop later wants the same video on connected TV screens, the CTV addendum from July 2024 is the next question. The addendum lists ACIF support for ad registration, icons to support DSA and higher-resolution creative for larger screens. The VAST 4.3 entry points to that addendum for ad creative support, so a version number alone does not answer the question.

Decision rule: from question to standard

Decision rule: If the question is how the ad is described to the player, check the VAST version and addenda. If the question is about a tappable or interactive layer, check SIMID support and version. If the question is about measurement, viewability or verification, check Open Measurement support. If the question is about connected TV screens, check the CTV addendum. If the question mentions VPAID, treat it as a migration item, not as a feature to build on.

Assumptions that cause disputes

• A recent VAST version does not mean the ad can be measured. Measurement is a separate question.
• SIMID support does not guarantee that every interactive ad works. The source says deep links need additional setup.
• The deprecated status of VPAID in the list does not describe how each player behaves with an old template. It only shows where the standard stands.
• Version 4.3 does not automatically carry the CTV addendum. The 4.3 entry sends readers to the addendum.
• A date on a standards page says nothing about the publisher's player.

Each item marks the edge of what a page says. Disputes between advertiser and publisher come from one side assuming more than the page states. A written declaration and a test run remove much of the room for such assumptions.

Neighboring topics: price, viewability, weight

VAST does not set prices, and it does not define how many seconds count as a view. For how video and display impressions are priced, see ad pricing models. For thresholds that decide whether an impression counts as viewable, see ad viewability and IAB standards. Page weight and layout stability sit with ads and Core Web Vitals, and slot sizes and positions for display ads are covered in banner ad space sizes and placements.

Keeping those conversations separate helps. A buyer can accept a VAST version, then separately negotiate the price model, then separately agree how viewability is judged. Mixing them leads to a stalled thread where no one is sure which question is open.

A version log for each publisher

A publisher's player is updated on its own schedule, apart from the standard. A short log makes it possible to see which answer was true on which day. Practical suggestion: keep one row per publisher and one per campaign.

The VAST 4.1 date mismatch shows why the log should say which source you used. If your contract quotes a release date, name the source next to it.

Acceptance checklist for the publisher side

A publisher accepting video ads is checking technical information that arrives with the creative. This checklist turns the version and addenda information on the VAST page into questions. It is a conversation guide, not a certification.

• The VAST version the ad follows is stated, together with any addenda such as the CTV addendum.
• Whether the ad has an interactive layer is stated, and if it does, SIMID support and version are confirmed.
• No new interactive creative depends on VPAID, which the page lists as deprecated.
• Measurement and verification route is stated, including whether Open Measurement is supported.
• Features that depend on SIMID 1.2, such as responsive ads, L-shaped ad space or deep links, were confirmed with the publisher before launch.
• A test run on the real player passed before the full campaign.

Practical suggestion: Keep the checklist in the booking form as a technical block. When a new advertiser arrives, the same questions are asked in the same order, and publisher and advertiser both see where an answer is missing. For the file side of the handoff, the creative brief and file handoff checklist is a suitable base.

Outside the scope

The IAB Tech Lab pages explain what VAST and SIMID are, which versions are listed and which standard replaced which. A test tool that tells you whether a player supports a version, a list of publishers with their supported versions and advice on configuring an ad server are all outside this topic. To learn what one particular player supports, ask the publisher or read the player's own documentation.

Video search markup, such as the schema that helps a video appear in search results, is outside this topic. VAST is an ad-serving standard. Click-through behavior, price and campaign results are likewise contract and measurement matters rather than VAST matters.

Frequently Asked Questions

How does the IAB Tech Lab define VAST?

According to the IAB Tech Lab, VAST is a universal XML schema for serving ads to digital video players. It also says it describes the video player behavior expected when VAST-formatted ad responses are executed.

Does the IAB Tech Lab name a current VAST version?

The IAB Tech Lab page does not label a current version. The latest core version it lists is VAST 4.3 from December 2022, followed in the list by the VAST Addendum for attribution reporting from July 2023 and the VAST Addendum for CTV 2024 from July 2024. The page was last updated on July 18, 2024.

In which VAST release did SIMID support arrive?

According to the VAST page, VAST 4.2 brought SIMID support, described as the replacement for VPAID for interactive use cases.

Which standard covers interactivity and which covers measurement?

Per the SIMID page, OMID handles measurement and verification while SIMID handles interactivity. The interactive layer and the media asset are kept separate, and both are delivered through VAST 4.x.

Is VPAID still the interactive standard?

No. The VAST text lists VPAID as deprecated and replaced with SIMID, which the SIMID page describes as a container that enables communication between the player and any ad creative.

Is VAST a video SEO signal?

The IAB Tech Lab pages contain no statement about search visibility. VAST is an ad-serving standard.

Conclusion

VAST describes how a video ad is presented to a player, SIMID covers the interactive layer, and OMID covers measurement and verification. Keep the three questions apart: version and addenda for VAST, interactive support for SIMID, measurement route for Open Measurement. The IAB Tech Lab page labels no current version. It lists VAST 4.3 as the latest core version and two later addenda, so write down the version your publisher declares and the date you read the page.

A publisher can place the same questions in its booking form, and an advertiser can place them in the brief. Both sides then arrive at the first call with the same vocabulary, and a delicatessen with a short video and a tappable hamper offer can run a campaign without finding out about player support after launch.

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