VAST Error 402: Media file timeout
The media file exists but couldn't be fetched in time — too large, too slow a CDN, or too little bandwidth.
Error 402 means the player found and requested the media file but gave up waiting for enough of it to start playback. The asset is reachable; the transfer is just too slow for the player's buffer budget.
It's a bandwidth-vs-file-size equation: oversized files, under-provisioned CDNs, and slow last-mile connections all show up here, hitting mobile and peak-hour traffic hardest.
Why error 402 happens
File too large for the placement
A 50 MB mezzanine-grade file trafficked where a 5 MB streaming encode belongs. First-frame buffering takes longer than the player waits.
Only high-bitrate renditions available
Without a rendition ladder, slow connections are forced to fetch a file sized for fast ones.
Slow or distant CDN edge
The creative's CDN has no presence near the user, so throughput is capped by intercontinental transit.
No range/streaming support on the host
Hosts that don't support progressive download force the player to wait for more of the file than it needs.
How to fix VAST error 402
- 1
Check file sizes across renditions
Inspect every MediaFile's actual size and bitrate. For streaming delivery, files should typically be single-digit megabytes for a 30-second spot.
- 2
Add low-bitrate renditions
Include ~500 kbps and ~1 Mbps options so constrained connections have a file they can buffer quickly.
- 3
Measure download time from user regions
Time the media file fetch from where your audience is. A file that fetches in 300 ms from your office may take 8 s from the affected geography.
- 4
Move assets to a real CDN
Creatives served from origin servers or single-region storage need proper CDN distribution.
Seeing error 402 on a live tag?
Paste the tag URL or XML — the validator resolves the full wrapper chain, validates the schema, downloads every media file, and shows exactly which stage fails.
Validate your VAST tagVAST error 402 — frequently asked questions
What file size should a 30-second video ad be?+
For streaming renditions, roughly 3–8 MB depending on resolution (≈1–2 Mbps encodes). Ship larger, higher-quality renditions alongside — not instead of — streaming-friendly ones.
Why does 402 spike on mobile?+
Cellular bandwidth is lower and more variable. Tags without low-bitrate renditions push mobile users onto files their connections can't buffer within the player's timeout.