What is VAST?
VAST (Video Ad Serving Template) is an industry-standard XML schema developed by the Interactive Advertising Bureau (IAB) that enables video players to request and display video advertisements from ad servers. Think of it as a common language that allows different video players and ad servers to work together seamlessly.
Before VAST, every video player and ad server had to implement custom integrations, making it expensive and time-consuming to connect different systems. VAST solved this by creating a universal protocol that the entire industry could adopt.
How VAST Works
When a viewer watches a video on a publisher’s website, here’s what happens behind the scenes:
- Ad Request: The video player sends a request to an ad server
- VAST Response: The ad server returns an XML document containing:
- URLs to the video ad creative (in various formats/sizes)
- Tracking URLs for impressions, clicks, and quartile events
- Duration and skip settings
- Companion ad information (optional)
- Ad Playback: The video player parses the XML and plays the appropriate video file
- Tracking: As the ad plays, the player fires tracking pixels at specified events
VAST Elements and Structure
A typical VAST response includes these key elements:
Ad Creative Information
- MediaFiles: URLs to the actual video files in different formats (MP4, WebM) and bitrates
- Duration: How long the ad runs
- ClickThrough: Where users go when they click the ad
Tracking Events
VAST supports comprehensive tracking:
- Impression: When the ad starts
- Start, FirstQuartile, Midpoint, ThirdQuartile, Complete: Progress milestones
- Pause, Resume, Skip: User interactions
- Error: When something goes wrong
Companion Ads
Display ads that appear alongside the video, typically in designated spaces on the page.
VAST Versions
The IAB has released several VAST versions, each adding new capabilities:
| Version | Key Features |
|---|---|
| VAST 2.0 | Basic linear/nonlinear ads, companions |
| VAST 3.0 | Ad pods, skippable ads, better error handling |
| VAST 4.0 | Mezzanine files, viewability, server-side verification |
| VAST 4.1 | Interactive creative files, closed captions |
| VAST 4.2 | Improved verification, universal ad ID, better macros |
VAST vs VPAID vs SIMID
Understanding the differences:
- VAST: Defines the ad response format and basic playback. The video player controls everything.
- VPAID: Allows the ad creative itself to take control, enabling interactive ads and custom tracking. Being deprecated due to performance and security concerns.
- SIMID: The successor to VPAID, providing interactivity while keeping the player in control.
Common VAST Implementation Challenges
Error Handling
VAST includes error codes (100-900) to help diagnose issues:
- 100-199: XML parsing errors
- 300-399: Wrapper/redirect errors
- 400-499: Linear ad errors
- 500-599: Nonlinear ad errors
- 600-699: Companion ad errors
Wrapper Limits
VAST ads can redirect (wrap) to other VAST responses. Too many wrappers increase latency and reduce fill rate. Most video players limit wrapper depth to 5.
Format Support
Publishers should ensure their video player supports multiple media types (MP4 H.264 at minimum) since ad creatives come in various formats.
VAST Best Practices for Publishers
- Use the latest version: VAST 4.x provides better tracking and verification
- Set appropriate timeouts: Don’t wait forever for slow ad servers
- Handle errors gracefully: Show content when ads fail
- Support multiple formats: Accept various video codecs and sizes
- Implement all tracking events: Complete tracking data improves yield
Video Player Integration
Modern video players like Veedmo handle VAST parsing and playback automatically, abstracting away the complexity. When evaluating a video player solution, check for:
- VAST 4.x support
- VPAID compatibility (for legacy campaigns)
- Proper error handling and fallbacks
- Complete event tracking
- Mobile and CTV support
Conclusion
VAST is the foundation of programmatic video advertising. Understanding how it works helps publishers optimize their video ad implementation, troubleshoot issues, and maximize revenue. As the standard continues to evolve with versions like 4.2, staying current ensures compatibility with the latest ad campaigns and measurement capabilities.