VAST Error 201: Video player expecting different linearity
The player asked for one linearity and got the other — a linear ad in a non-linear slot, or a non-linear overlay in a pre-roll.
Linear ads take over the video (pre/mid/post-roll); non-linear ads overlay it while content keeps playing. Error 201 fires when the response's linearity doesn't match what the placement requested.
It's common in chains where an intermediary re-brokers demand: the original request asked for an overlay, but a linear video ad won the auction somewhere upstream.
Why error 201 happens
Linear creative trafficked to an overlay slot (or vice versa)
The line item's creative type doesn't match the placement's linearity. Overlay slots can't take over the stream; pre-roll slots can't render overlays.
Wrapper chain crossing linearity boundaries
A wrapper requested with linearity constraints resolves to a demand source that ignores them, returning whatever creative filled.
Missing or wrong linearity attribute
Some responses omit the Linear/NonLinear structure the player expects, or declare it inconsistently between wrapper and inline.
How to fix VAST error 201
- 1
Inspect the resolved creative's linearity
Resolve the full chain and check whether the final inline ad is Linear or NonLinearAds, then compare with the placement type.
- 2
Enforce linearity in the ad request
Pass the placement's linearity requirement upstream (most SSPs support it) so demand that can't comply is filtered before it wins.
- 3
Separate line items per linearity
Never let one line item serve both overlay and takeover creatives; split them so targeting can't cross-match.
Seeing error 201 on a live tag?
Paste the tag URL or XML — the validator resolves the full wrapper chain, validates the schema, downloads every media file, and shows exactly which stage fails.
Validate your VAST tagVAST error 201 — frequently asked questions
What's the difference between linear and non-linear ads?+
Linear ads pause or replace the content video (pre-roll, mid-roll, post-roll). Non-linear ads render on top of the playing content, like a banner overlay across the bottom third.
Can a wrapper fix a linearity mismatch?+
No — wrappers only point at other VAST documents. The mismatch has to be fixed at trafficking or by filtering demand in the request.