Every video ad you see on a publisher site is the result of a short conversation between the player, an ad server and often several demand partners. That conversation runs on a handful of industry standards whose acronyms appear in every media kit and integration document. Here is what each one does, in plain English.
VAST: the ad’s instruction sheet
The Video Ad Serving Template, or VAST, is an XML document that tells a video player everything it needs to show an ad:
- Where to fetch the video file, usually in several sizes and encodings.
- How long the ad lasts, and whether and when it can be skipped.
- Which URLs to call when the ad starts, reaches its quartiles and completes, so everyone can count what happened.
- Where to send the viewer if they click.
When a player requests an ad, it receives a VAST response and follows its instructions. VAST responses can also point to other VAST responses, a process called wrapping, which is how an ad passes through several systems before it reaches the player. Every extra wrapper adds a little delay, which is one reason supply chains should be as short as possible.
VPAID: interactive ads, now mostly retired
The Video Player-Ad Interface Definition, VPAID, let an ad run its own code inside the player. It enabled interactive ads, but it also let creatives run heavy scripts, slow pages and, in some cases, hide invalid activity. The industry has largely moved away from it in favour of safer approaches.
If a partner still asks for VPAID, it is worth asking why and what the alternative is.
SIMID: interactivity without the risk
The Secure Interactive Media Interface Definition, SIMID, is the successor for interactive video ads. The interactive layer runs separately from the video itself, so the player stays in control and the ad cannot take over the page.
VMAP: when ads should play
The Video Multiple Ad Playlist, VMAP, describes where ad breaks go in longer content: before the video, at points in the middle and at the end. It is most relevant for longer-form content and connected TV, where a programme has several breaks. For short-form clips it is less common.
OMID: measurement you can trust
The Open Measurement Interface Definition, often called OM or OMID, gives third-party verification providers a standard way to measure viewability and check for invalid traffic inside the player. Buyers increasingly expect it, because it means they do not have to rely only on the seller’s numbers.
How it fits together
A simplified flow for a single ad:
- The player reaches an ad opportunity and asks the ad server for an ad.
- The ad server runs its decision, often including an auction among demand partners through Prebid, OpenRTB or Google Ad Manager.
- The winning demand returns a VAST response, possibly wrapped.
- The player follows the VAST instructions, plays the ad and fires the tracking calls.
- Verification scripts measure what was actually seen.
What publishers should ask for
When you evaluate a player or ad server, a few questions go a long way:
- Which VAST versions do you support? Recent versions carry better information about ad categories and verification.
- How do you handle long wrapper chains? Timeouts and limits protect page speed.
- Do you support Open Measurement? Buyers will ask.
- How do you filter creatives? Heavy or badly built ads should never reach readers.
- Which demand integrations can I use? You should be able to keep the partners you already work with.
These standards are the plumbing behind every format we run. Our ad server page explains how demand from Prebid.js, Prebid Server, OpenRTB, Google Ad Manager and Amazon comes together in one place, and our glossary covers the rest of the vocabulary.
