What is VAST (Video Ad Serving Template)?
VAST, the Video Ad Serving Template, is a standard published by IAB Tech Lab that defines how video ads are passed from an ad server to a video player. A VAST response is an XML document that tells the player which video file to play, how long it is, where to send people who click, and which tracking URLs to call as the ad plays.
Because almost every video player and ad platform supports VAST, one tag can run across many publishers, apps and connected TV services.
How VAST works
A video player reaches an ad break and requests an ad from its ad server or SSP.
The response comes back as VAST XML, either containing the ad directly or pointing to another server.
The player reads the XML, picks a media file it can play and starts the ad.
As the ad plays, the player fires tracking events back to the listed URLs.
Common tracking events include:
Impression: the ad started to play.
Quartiles: start, first quartile, midpoint, third quartile and complete.
Interactions: click, pause, mute, skip and errors.
These events power metrics such as video completion rate and cost per completed view.
Inline vs wrapper tags
An inline VAST response contains everything needed to play the ad, including media file URLs. A wrapper response points to another VAST URL, often because an advertiser ad server or verification vendor wants its own tracking in the chain. Wrappers are common, but long chains of them add delay and raise the risk of errors and timeouts, so keep them short.
Why VAST matters
Interoperability: a standard format lets one creative run across many players and platforms.
Measurement: consistent events make it possible to compare delivery and completion across publishers.
Connected TV readiness: CTV and server-side ad insertion depend on clean VAST responses with suitable media files. Newer VAST 4.x versions added features such as separate mezzanine files for high-quality transcoding and better support for server-side delivery.
VAST vs VPAID
VPAID (Video Player-Ad Interface Definition) was an older IAB standard that let ads run interactive code inside the player. It was widely used for interactivity and verification, but it caused slow loading, security concerns and poor support on mobile and CTV. IAB Tech Lab has deprecated VPAID. Its jobs are now handled by VAST 4.x together with Open Measurement (OM SDK) for verification and SIMID for interactive elements. VAST delivers and tracks the ad; VPAID tried to run code inside it.
VAST with AdGeeks
AdGeeks runs video and CTV campaigns on DV360, Amazon DSP and Adform, using hosted video files or your own VAST tags. Our traders check tags for supported formats and tracking before launch, so delivery and completion data hold up. See our ad formats, or request access.
