What is VAST?
VAST (Video Ad Serving Template) is a standard XML format for serving video and audio ads. Originally created for video advertising, VAST enables dynamic ad insertion in podcasts by providing a standardized way for ad servers to communicate with players.
How VAST Works in Podcasting
Episode requested
↓
Podcast server requests ad from ad server
↓
Ad server returns VAST XML with:
- Ad creative URL (audio file)
- Tracking URLs
- Duration
- Metadata
↓
Podcast server stitches ad into episode
↓
Player reports tracking events
VAST XML Structure (Simplified)
<VAST version="4.0">
<Ad>
<InLine>
<Creatives>
<Creative>
<Linear>
<Duration>00:00:30</Duration>
<MediaFiles>
<MediaFile type="audio/mpeg">
https://ads.example.com/audio/spot123.mp3
</MediaFile>
</MediaFiles>
<TrackingEvents>
<Tracking event="start">https://track.example.com/start</Tracking>
<Tracking event="complete">https://track.example.com/complete</Tracking>
</TrackingEvents>
</Linear>
</Creative>
</Creatives>
</InLine>
</Ad>
</VAST>
VAST Tracking Events
| Event | When Fired |
|---|---|
start |
Ad begins playing |
firstQuartile |
25% played |
midpoint |
50% played |
thirdQuartile |
75% played |
complete |
Ad finished |
VAST Versions
| Version | Key Features |
|---|---|
| VAST 2.0 | Basic ad serving |
| VAST 3.0 | Ad pods, skipping |
| VAST 4.0 | Improved verification, mezzanine files |
| VAST 4.1 | Better audio support |
| VAST 4.2 | Enhanced server-side tracking |
Why It Matters
VAST is the technical standard that enables programmatic advertising and sophisticated dynamic ad insertion in podcasting. Understanding VAST helps you work with advertising platforms and troubleshoot ad delivery issues.
Why VAST matters:
-
Industry standard: All major ad platforms speak VAST—it's the common language.
-
Programmatic enabler: VAST makes automated ad buying/selling possible.
-
Tracking capability: Standardized events allow consistent measurement.
-
Platform compatibility: VAST-compliant systems can exchange ads seamlessly.
VAST in the podcast ecosystem:
| Component | Role |
|---|---|
| Your hosting platform | Requests and stitches VAST ads |
| Ad networks | Serve VAST ad responses |
| Advertisers | Provide VAST-compliant creatives |
| Analytics | Use VAST tracking for reporting |
Practical implications:
| Scenario | VAST Relevance |
|---|---|
| Using DAI | Your platform handles VAST automatically |
| Debugging ad issues | VAST errors appear in logs |
| Working with agencies | They'll mention VAST compliance |
| Programmatic setup | Requires VAST-compatible systems |
Technical evolution: Podcast-specific extensions to VAST continue to develop, addressing unique needs like audio-only content, offline playback, and RSS-based delivery.