CTV & video · also called Video Ad Serving Template
VAST
VAST (Video Ad Serving Template) is the IAB Tech Lab standard XML format that tells a video player which ad to play, where to fetch it and which tracking events to report.
When a video player or SSAI server asks for an ad, the ad server replies with a VAST document. It contains the ad's media files (usually in several formats and sizes), its duration, click-through URL and tracking URLs to call at key moments: impression, start, quartiles, completion, pause, skip and errors. Without a common format, every player would need custom code for every ad server.
VAST was first released in 2008 and has gone through several versions. VAST 4 introduced improvements important for CTV and SSAI, such as separating the ad's video file from interactive code, a universal ad ID for identifying creatives across systems, an AdVerification element for measurement scripts, and better support for server-side stitching. VAST responses can be "wrapped", pointing to another VAST, which adds flexibility but also latency and opacity.
VAST works with VMAP for scheduling ad breaks, SIMID for interactivity, and the Open Measurement SDK for verification. Tracking events in VAST feed video completion rate metrics; because they can be faked, verification matters in CTV fraud.
Think of it like this
VAST is like a standard shipping label on a parcel: it tells any courier what is inside, where to deliver it and whom to notify at each stage.
An example
A CTV app's ad call returns a VAST 4 document with a 30-second ad in three bitrates, a universal ad ID, and tracking URLs that fire at 0%, 25%, 50%, 75% and 100% of playback.
Related terms
VPAID
VPAID (Video Player-Ad Interface Definition) is an older IAB standard letting interactive ad code run inside video players, now deprecated in favour of SIMID and OM SDK.
VMAP
VMAP (Video Multiple Ad Playlist) is an IAB Tech Lab XML standard describing where ad breaks fall in a video, such as pre-roll, mid-roll and post-roll slots.
SIMID
SIMID (Secure Interactive Media Interface Definition) is an IAB Tech Lab standard for adding interactive elements to video ads, while leaving the video player in control of playback.
SSAI (server-side ad insertion)
SSAI (server-side ad insertion) stitches video ads directly into the content stream on a server before it reaches the viewer, creating seamless, TV-like playback that ad blockers find hard to detect.
Video completion rate (VCR)
Video completion rate (VCR) is the percentage of video ads that played all the way to the end, out of those that started playing.
Sources: IAB Tech Lab VAST