VAST Prefetch Requests

What is VAST?

The IAB’s Video Ad Serving Template (VAST) specification is a universal XML schema for serving ads to digital
video players. It provides support for linear pre-roll, mid-roll and post-roll MP4/FLV/WebM video ads as well
as non-linear GIF/JPG/PNG, Flash (SWF), text, HTML, <IFRAME> and <SCRIPT> banners. In addition to this
it also specifies video tracking events, which enables measurement of video advertising consumption.

Prefetch Requests

Upon loading, a video player will often prefetch the VAST tag from the ad server
to speed up the process of displaying pre-roll video ads. This is especially helpful
when dealing with click-to-play videos. When a visitor clicks the play button the
video player already knows the pre-roll video ad location and can start playing it instantly.

Tracking Prefetch Requests

This is rather interesting because AdvertServe actually tracks those prefetch requests.
For click-to-play videos, this gives you the opportunity to see how many visitors
did not initiate playing. Various things can be inferred from this, but the most
obvious would be if your video player has a low play rate it might not be in a
visible enough location on your page. Another factor affecting play rate could be
a poor call to action. Most video players give you the option to display a splash image,
which if done properly should capture a visitors attention.

Sample Report

All video reports available through AdvertServe include a Requests column side-by-side with a Views
column so you can quickly and easily compare prefetch requests to play initiations.

AdvertServe: Video Report

As you can see from the above sample report (click to enlarge), we have a pretty good
rate of play initiation!

Final Thoughts

Hopefully you will find prefetch request tracking to be insightful at some point. Want to learn
more about video ad serving? You’ll find many more articles about
VAST on this blog, which cover topics such
as pre-rolls, mid-rolls, post-rolls, third-party ads, companion banners and overlays.

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