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IAB Video Ad Serving Template (VAST)

Appendix A: Ad Tag Format Recommendation

In order to minimize the size of the XML response from Ad Servers and to reduce the possibility of video ads being returned that do not meet the publisher specs, it is recommended that Ad Servers implement certain pre-defined parameters in their ad tags. While the syntax of Ad Server tags differs between vendors and technologies, using common values within these tags will enable Primary Ad Servers and Video Players to simplify and automate executions.

It is preferable for Ad Servers to return XML that only includes information relevant to the request, however, there is no requirement that extraneous information be stripped out. For example, if a Video Player requests a Flash video, the response may include nodes for both a Flash video and a Windows Media video as well. Some Secondary Ad Servers may be unable to respond dynamically to these parameters and whether this is acceptable to Publishers will be a matter of business negotiation.

The recommended parameters are shown in the table below.

  • Parameters are abbreviated to minimize URL length.

  • Parameters are case-sensitive.

  • Multiple comma-separated values may be assigned to a parameter (e.g. VMaxd=15,30). Multiple values should

be considered as an OR request, meaning that either value is acceptable.


Acceptable Va


Any integer value





Any integer value Any integer value Any integer value

Notes Maximum duration of video accepted, in seconds. Player frameworks accepted. These values do not reflect specific video file extensions, but rather are abbreviations for the three currently supported player types. As the VAST document is extended to other player types additional abbreviations may be added. Expected height of video in pixels Expected width of video in pixels Maximum bandwidth of video requested in bits per second.

Examples using a fictional Ad Server are shown below. The actual syntax of these requests is likely to differ between Ad Servers.

Sample Ad Tag http://ad.server.com/site/content?random=1234

http://ad.server.com/site/content?Vmaxd=30;ran dom=1234

http://ad.server.com/site/content?Vln=30;VPl=W MP,FLV;random=1234

Explanation Base ad tag with random number inserted. This ad tag will return any video ad within the Ad Server without regard to what the Video Player is expecting. The video duration is specified as 30 seconds and the Video Player expects the Ad Server to return an XML document specifying a 30- second spot. Since the player and bandwidth are not specified, the Secondary Ad Server can respond with ads meeting any or all such criteria. In addition to requesting a 30-second spot, the Video Player indicates that it wants either a Windows Media Player-compatible video XML or a Flash-compatible video XML.

© 2008 Interactive Advertising Bureau

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