Quartile Events

Quartile events are the four VAST tracking pixels that fire at 25%, 50%, 75%, and 100% of video ad playback. Named in spec as "firstQuartile", "midpoint", "thirdQuartile", and "complete". Each is a separate URL that the player calls when its current playback position crosses the relevant threshold. The "start" event fires at 0% (impression beacon); the four quartile events trace the progression.

Quartile events are the spine of CTV / DOOH completion analytics. Completion rate is firings of "complete" / firings of "start". Drop-off curves at each quartile reveal where viewers (or screens) lose the playout. A clean drop curve looks like 100% / 98% / 96% / 94% / 92% — a steep drop between any two indicates a problem (decode failure, mid-roll skip, screen power-off).

Each pixel is independent — there's no rule that "midpoint" must fire after "firstQuartile". In practice, IMA-style players fire them in order with strict deduplication (one firing per pixel per playout) but the spec doesn't mandate it. Buyers running attribution should check pixel ordering as a sanity check; out-of-order quartiles often signal player bugs or impression fraud.

On Trillboards screens, quartile events are fired locally on-device and batched to the API every 30 seconds to reduce wakeups — see edge inference and the proof-of-play ledger for the per-impression timestamp.