VAST (Video Ad Serving Template) is the IAB standard an ad server uses to describe a video ad to a player or ad stitcher: where to fetch the creative, its duration, and the tracking/beacon URLs to fire at events like start, quartiles, and complete. It is the lingua franca between the demand side (ad servers, exchanges) and the playback side.
VAST handles a single ad (or a wrapper that redirects to another ad server). Its companion VMAP (Video Multiple Ad Playlist) describes the ad schedule — which breaks exist in a piece of content and what goes in each (pre-roll, mid-rolls, post-roll). Together they let a player or SSAI stitcher request, schedule, and report on ads in a vendor-neutral way.
Both SSAI and CSAI rely on VAST/VMAP: in CSAI the player's ad SDK consumes them directly; in SSAI the stitcher consumes them server-side and weaves the resulting creatives into the stream. Correct VAST tracking is what makes ad impressions countable and billable.
The handbook · 7 volumes
Fora Soft Video Engineering Handbook
VAST tells a player or stitcher which creative to fetch and which tracking beacons to fire, and broken VAST responses are a common cause of empty ad slots. We wrote seven volumes covering the video stack; for VAST start with Volume 3 on players and streaming economics, then Volume 2 on manifests and ad markers, with encoding in Volume 1. Written by Nikolay Sapunov, CEO at Fora Soft.
VAST errors leaving ad slots empty or impressions uncounted?
We will audit your VAST and VMAP flow and send a fix list with timeouts, fallbacks, and tracking checks. 250+ video products shipped since 2005.
