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.
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.
Mike Cherichetti
