Quartiles are a standard method for measuring the effectiveness of audio ads by determining what percentage of a given creative was heard by a user.
As the ad playback reaches every quarter of the total ad duration, the player fires a quartile report. Along with the start and complete events, there are five events to report. The URI to be fired to report each event is provided in <Tracking> elements under:
<VAST><Ad><InLine><Creatives><Creative><Linear><TrackingEvents>
Each <Tracking> element contains an "event" property that defines what event this element is for (there could be multiple <Tracking> elements for the same event).
start: This event indicates that an individual creative within the ad was loaded and playback began.firstQuartile: The creative played continuously for at least 25% of the total duration at normal speed.midpoint: The creative played continuously for at least 50% of the total duration at normal speed.thirdQuartile: The creative played continuously for at least 75% of the duration at normal speed.complete: The creative was played to the end at normal speed so that 100% of the creative was played.
For podcast listening via download, ad delivery is done at the file level so quartiles are based on download percentage instead of listen-through. As such, download podcast quartiles will typically all be at 100% (unless the download is interrupted).