VAST
VAST (Video Ad Serving Template) is an IAB standard XML format that ad servers use to tell a video player which ad to play and how to track it. A VAST tag holds the ad's media file links, duration, click-through URL and tracking URLs for events like impressions and completions. It lets any compliant player work with any compliant ad server.
Why it matters
VAST is the common language of video advertising. Without it, every player would need custom work for each ad network. Supporting VAST opens a video product to a wide range of advertisers and ad exchanges, and gives advertisers the tracking they need to pay.
How it works
- The player calls an ad server using a VAST tag URL.
- The ad server returns an XML document describing the ad.
- The XML lists media files, duration, click-through link and tracking URLs.
- The player picks a suitable media file, plays it and calls the tracking URLs at key moments.
What is the difference between VAST and VPAID?
VAST describes which ad to play and how to track it, while VPAID let interactive ad code run inside the player. VAST is a data format, and VPAID was an interface for code. VPAID is now deprecated, and interactivity has moved to SIMID, which is used alongside VAST.
Which VAST version should I use?
Most teams should support VAST 4.x, while keeping fallback support for older versions that some ad servers still send. Newer versions add features such as ad verification and better handling of server-side insertion. Check what your ad partners deliver before choosing.
What is a VAST tag?
A VAST tag is a URL that a video player calls to get an ad in VAST format. The URL usually includes details such as page, device or content information. The ad server replies with XML that tells the player which ad file to play and where to send tracking events.
Where it's used
OTT services, microdrama apps and creator platforms use VAST so their players can show ads from many ad networks without custom work. Advertisers rely on its tracking to confirm views.
By the numbers
- IAB Tech Lab released VAST 4.0 for public comment on November 2, 2015, the first update to the template since 2012. (IAB Tech Lab releases VAST 4.0 for public comment (IAB))
- IAB Tech Lab lists VAST 4.2, released in June 2019, as the version that added support for interactivity with SIMID. (VAST (IAB Tech Lab))
