What is VAST in video advertising?
VAST (Video Ad Serving Template) is the IAB Tech Lab's standard format that ad servers use to tell a video player which ad to play, where the video files are, and which tracking URLs to call at events such as start, midpoint and completion. It lets any compliant player show ads from any compliant ad server.
A VAST response is an XML document. Versions 4.x added support for SSAI, ad verification scripts and universal ad IDs. VPAID, an older standard that ran interactive code inside players, was deprecated in favour of SIMID for interactivity and OM SDK for measurement, partly because VPAID was abused for fraud.
VMAP schedules multiple ad breaks, and ad pods group several ads in one break. VAST "wrappers" that redirect to other servers add latency and can hide where ads come from.