VAST error codes / Linear and media errors
VAST error 407: Mezzanine downloading
Short answer: The mezzanine is still being downloaded and transcoded. Introduced in VAST 4.1.
Debug this tag now
If you only have a live URL, test it first. If the failure is in the wrapper chain, inspect each hop. Validate resolved XML when you already have the response.
What your player reported
407· Mezzanine is in the process of being downloaded for the first time. Download may take several hours. Ad will not be served until mezzanine is downloaded and transcoded.
Wording from the IAB VAST 4.3 specification error table. Players may shorten or reformat it, but the code is the same.
What it means
Not strictly an error: the mezzanine is being fetched for the first time, so the ad will not serve until transcoding completes.
Common causes
- First-time mezzanine ingestion in progress
How to fix it
Expected on first sight of a new creative. Confirm the ad serves on later requests once transcoding finishes.
VAST error codes are runtime buckets emitted by the player. They tell you where the failure happened, not which line of XML caused it. Paste the raw tag into the validator to map this code onto the exact element and rule.
Related vastlint rules
- VAST-4.1-mezzanine-type: <Mezzanine> missing required type attribute
Related error codes
Debug this tag now
Validate the XML, follow the wrapper chain, or check it in CI before launch:
# CLI: exits non-zero on errors, ideal for pipelines
vastlint check creative.xml