VAST error codes / Linear and media errors
VAST error 403: No supported media file
Short answer: No MediaFile matched a type/format the player can play.
Test the resolved tag
VAST error 403 is a media-file mismatch. Test the live URL to see which MediaFile the player would pick, then inspect wrappers if the chain never reaches InLine.
What your player reported
403· Couldn’t find MediaFile that is supported by this media player, based on the attributes of the MediaFile element.
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
Media files were present, but none had a MIME type, delivery method, or API framework the player supports.
Common causes
- Only formats the device cannot decode (e.g. browser-only on CTV)
- Deprecated VPAID/Flash media where the player needs MP4/HLS
- Missing or wrong `type` / `delivery` attributes
How to fix it
Make sure at least one `<MediaFile>` is a widely supported progressive or adaptive format with correct `type` and `delivery`.
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-2.0-mediafile-type: <MediaFile> must have a type attribute
- VAST-2.0-mediafile-delivery: <MediaFile> must have a delivery attribute
- VAST-2.0-flash-mediafile: Flash-based MediaFile type is no longer supported
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