vastlint
VAST-2.0-linear-tracking-quartiles

VAST-2.0-linear-tracking-quartiles

<Linear> has no standard quartile tracking events — measurement system receives no signal

WarningAmbiguousIAB VAST 4.1 §3.14.2VAST 2.0 and later (all versions)

Short answer

A <Linear> creative with no <TrackingEvents> containing any of start, firstQuartile, midpoint, thirdQuartile, or complete will serve and deliver impressions but return zero measurement signal. The advertiser's reporting system has no way to verify viewability or completion rates. While the VAST spec marks <TrackingEvents> as optional (minOccurs=0), omitting all five standard quartile events is a complete measurement blackout in practice.

Why this matters in production

This rule is a strong risk signal. Tags with this issue often still parse, but they become brittle across SDKs, SSAI resolvers, and CTV environments. Ambiguous rules matter because undefined behavior shifts between vendors. Fixing them reduces the chance that two standards-compliant systems interpret the same tag differently. Affected scope: VAST 2.0 and later (all versions).

Invalid

<Linear>
  <Duration>00:00:30</Duration>
  <!-- no <TrackingEvents> — measurement system receives no signal -->
  <MediaFiles>
    <MediaFile delivery="progressive" type="video/mp4" width="1280" height="720">
      <![CDATA[https://example.com/ad.mp4]]>
    </MediaFile>
  </MediaFiles>
</Linear>

Valid

<Linear>
  <Duration>00:00:30</Duration>
  <TrackingEvents>
    <Tracking event="start"><![CDATA[https://example.com/track?e=start]]></Tracking>
    <Tracking event="firstQuartile"><![CDATA[https://example.com/track?e=q1]]></Tracking>
    <Tracking event="midpoint"><![CDATA[https://example.com/track?e=mid]]></Tracking>
    <Tracking event="thirdQuartile"><![CDATA[https://example.com/track?e=q3]]></Tracking>
    <Tracking event="complete"><![CDATA[https://example.com/track?e=complete]]></Tracking>
  </TrackingEvents>
</Linear>
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Other Ambiguous rules

VAST-3.0-progress-offset<Tracking event="progress"> requires an offset attributeVAST-3.0-icon-attrsIcon missing recommended attributes (program/width/height/position)VAST-2.0-nonlinear-dimensions<NonLinear> missing required width or height attributesVAST-2.0-companion-dimensions<Companion> missing width or heightVAST-4.0-wrapper-clickthrough<ClickThrough> inside Wrapper <VideoClicks> was removed in VAST 4.0 (re-allowed in 4.2)VAST-4.2-icon-fallback-image-width-height<IconClickFallbackImage> should have width and height attributes