Digital Video Ad Serving Template (VAST)

VAST 4.3

Released December 2022

VAST 4.2

Released: June 2019

(updated October 2019 with corrections – listed in Section 8)

Highlights: Secure Interactive Media Interface Definition (SIMID) – the replacement for VPAID for interactive use cases and a few other minor updates.

VAST 4.1

Released: November 2018

Highlights: Updates for Improved Ad Verification, Ad Creative Measurement, Server-Side Ad Insertion and Integration of Audio Advertising

This revision of VAST includes updates that addresses most of the gaps identified in VAST 4.0. The Digital Video Technical Working Group expects VAST 4.1 to be the first version of VAST4 to be widely adopted.  The following are highlights of the changes introduced in VAST 4.1:

  • Verification: Changes that enable verification to be supported in a non-VPAID architecture (separated from media file). Also includes changes necessary to work with Open Measurement.
  • Digital Audio Ad Serving Template (DAAST): With VAST 4.1, DAAST has been merged into VAST.
  • Ad Requests: VAST is a response protocol. 4.1 now includes a basic Ad Request specification, based on macros.
  • Server-Side Ad Insertion (SSAI) related changes: VAST 4.1 includes minor changes to how headers should be handled. The “Ad Request” section is also relevant to SSAI use cases.
  • Deprecating Video Player Ad-Serving Interface Definition (VPAID): With VAST 4.1 we are taking the first steps to officially deprecate the use of VPAID.
  • AdServingID: A field to simplify comparing data about a video impression across the various systems involved with the delivery and tracking of the impression.
  • VAST Interactive Templates: Address the need for interactive ads without ad delivered executable code.
  • Closed Captioning: Standardizing the delivery of Closed Captioning files.

For more details, please download the VAST 4.1 specification.

Open Measurement updates:

OMID 1.2 includes API changes to support Open Measurement in web environments. The Open Measurement Working Group has also provided an implementation guide for 3rd parties to implement Open Measurement for web.  More information available here

VAST 4.1 Blog Series

Upgrading Video Ad Delivery Workflows with VAST 4.1|Simplifying Interactivity Standards with VAST 4.1| Now with Audio Power | The Long Awaited Video Verification Solution! | IAB Tech Lab Releases Final Version of VAST 4.1

VAST 4.0 

Released: April 2016

Overview of VAST 4.0

Developed by members of the IAB Digital Video Technical Standards Working Group, the revision offers improvements for the delivery and measurement of video advertising, including sophisticated delivery and tracking options for clients, the ability to select ads dynamically for insertion, and a more seamless experience for the viewer.

VAST is a Video Ad Serving Template for structuring ad tags that serve ads to video players. Using an XML schema, VAST transfers important metadata about an ad from the ad server to a video player. Initially launched in 2008, VAST has since played an important role in the growth of the digital video marketplace.

The early days of video consisted mostly of shared videos and other user-generated content. Success in monetizing this content with ads has produced the resources to improve the digital video marketplace. However, digital video has met a number of challenges along the way.

One challenge, and a key reason some video publishers avoid using VAST, is a lack of quality control. Along with the IAB Video Player-Ad Interface Definition (VPAID), VAST can deliver ads programmatically or include ads with complex interactions. If a player isn’t programmed to accept VPAID ads, the ad cannot be executed. Even when the player does accept VPAID ads, performance may be slow and cause latency in load times. In the meantime, the audience experiences a delay or a malfunction in their viewing experience.

Publishers and ad vendors need a way to separate the video file from its interactive components to ensure that ads play in systems that cannot execute the interactive components. These ads should also execute more efficiently in players that are equipped to handle the interactions.

Another challenge, especially for broadcasters who are moving their content online, is the lack of a consistent identifier for creative that is maintained across systems. VAST offers a creative identifier, but it has been used inconsistently and one creative may use different identifiers for every system it passes through. A system-wide identifier is a requirement for broadcasters trying to maintain control over the ads they play.

VAST 4.0 has addressed these challenges along with a few others. As players begin to adopt the updates in VAST 4.0, digital video can expect to see smoother operation and continued growth.

The updates made in VAST 4.0 and the challenges they address are summarized here:

  • Separate Video File and Interactive File: The complexity of digital video has given rise to the need to separate the linear video file from any creative interactive API files. While the VAST media file has accepted a variety of media files in the past, interactive APIs cannot always be executed. A VAST tag that provides the video file separate from APIs can display more successfully across platforms and devices.
  • Server-side Support: While client-side ad execution and tracking has been the recommended way to track ad impressions and other metrics, digital in-stream video ads are often served to devices (clients) that cannot execute and track ads using traditional display methods. VAST 4.0 supports the increasingly common “ad- stitching” method for stitching linear video ads into a video content stream and sending it to players with limited capabilities.
  • Mezzanine File: To support advertising across video platforms that include long-form content and high-resolution screens, VAST 4.0 features include support for the raw, high-quality mezzanine file. The mezzanine file is very large and cannot be used for ad display, but ad-stitching services and other ad vendor use it to generate files at appropriate quality levels for the environment in which they play.
  • Ready-to-serve Files: Along with support for including the mezzanine file, VAST 4.0 provides guidance on providing three ready-to-serve video files, each at different quality levels, to ensure that a linear video ad can always play. The IAB Digital Video Ad Format Guidelines offers guidance on video file specifications for linear ads.
  • Universal Ad ID: While VAST has offered a creative identifier in the past, it has been used inconsistently. The new Universal Ad ID feature is used specifically for including a creative identifier that is maintained across systems. The existing adId attribute for creative can still be used to log creative IDs specific to the server.
  • Ad Verification and Viewability Execution: Verification vendors have been using VPAID for measurement verification instead of using it for ad interaction as VPAID was intended. VAST 4.0 offers a designated space for inserting ad verification APIs, enabling a more streamlined process for executing files strictly intended for ad verification. In addition, a secondary impression element, the <ViewableImpression> element, has been added to allow publishers the option to track viewability on their inventory.
  • Support for Categories: Ad categories help video publishers separate competing ad creative and improve brand safety. VAST 4.0 ad categories support these efforts.
  • Conditional Ad Declaration: In programmatic environments, a VPAID unit is sometimes used to decide whether or not to place an ad. If this “conditional ad” never results in an ad to display, the publisher may have to forfeit any revenue from the resulting lost inventory. A declaration in VAST for a conditional ad helps publishers prevent and reclaim any potentially lost inventory revenue in programmatic ad delivery.
  • New Error Codes: Along with support for the mezzanine file and other new features, added error codes provide additional troubleshooting support.
  • Standardized Time Stamp: Trackers used in VAST often include timestamp macros, but its use has not been consistent. In VAST 4.0, the [TIMESTAMP] macro and the format for time has been standardized to enable more consistent time-sensitive tracking.

Intended Audience

This document was designed for digital video technologists who either develop players that accept digital in-stream ads or for vendors who develop ads to be sent to digital in-stream players.

For engineers, section 3 defines all the VAST XML elements. Section 5 includes a “human- readable” schema for quick reference with links to more details in the document if needed. Section 2 defines VAST compliance and section 4 provides technical tips for migrating to VAST 4.0.

For video executives, the executive summary and section 1 provide high-level explanation of how VAST can be used to streamline digital video ad operations.

Previous Versions
Version Release Date
VAST 4.1 (PDF) November 2018
VAST 4.0 (PDF) January 2016 (error corrections April 2016)
VAST 3.0 (PDF) July 2012
VAST 2.0 (PDF) March 2012
VAST 1.0 No longer supported

Supporting Resources

IAB Tech Lab Releases VAST 4.1 (Blog post)

IAB Tech Lab Releases VAST 4.1 for Public Comment (Press Release)

Five Use Cases for Video Ad Serving (PDF)

IAB Digital Video In-Stream Ad Format Guidelines (PDF)

Understanding & Adopting VAST 4.0 (Webinar)

Tech Lab CodeBank: VAST (PDF)

Video Multiple Ad Playlist (VMAP)

Video Player-Ad Interface Definition (VPAID)

DAA Ad Marker Implementation Guidelines for Video (PDF)

VAST 4.0 Arrives, Championing the Technology Behind the Growth of Digital Video Advertising (Blog)

Developed by the Digital Video Technical Standards Working Group

IAB Tech Lab Contact

Katie Stroud
Senior Product Manager