Glossary
What is VAST?
Also called: Video Ad Serving Template, VAST tag
VAST (Video Ad Serving Template) is the IAB standard XML a video player receives to know which ad to play and which tracking links to call.
हिंदी में पढ़ेंWhen a video player reaches an ad break, it calls an ad server and gets back VAST, an XML template defined by IAB Tech Lab; the current version is 4.3. The reply comes in two shapes. An InLine response holds the ad itself: an impression link to ping when it starts, its duration, and media files, the video in several sizes. A Wrapper says: ask this other server instead.
VAST also lists tracking events: start, first quartile, midpoint, third quartile and complete. The player fires each one, so the buyer knows how far the ad played. When something fails, the player reports a numbered error code.
Every Wrapper adds a round trip. After more than five, the player may give up on the chain and report error 302, wrapper limit reached; 303 means no ad came back after the wrappers. Pasting a tag into a VAST tester, such as IAB Tech Lab’s, shows how many Wrappers it passes through.
Example
A tag passes through 3 Wrappers before it reaches the InLine ad, so the player makes 4 calls in total before the video can start. With 6 Wrappers the chain is over the limit of 5, and the player may stop and report error 302.
Why it matters to publishers
Long Wrapper chains slow ads down and lead to failed breaks that earn nothing. Knowing how your tags resolve is basic hygiene for video revenue.