VAST-4.1-mezzanine-recommended
<MediaFiles> has no <Mezzanine> — may be rejected in CTV/SSAI contexts
Short answer
Many CTV ad servers and SSAI platforms require a <Mezzanine> element pointing to a high-quality source file for server-side transcoding. Without it, the ad may be rejected during trafficking.
Why this matters in production
This rule is advisory rather than fatal, but it still matters for portability, debugging speed, and keeping tags predictable across different buyers and playback stacks. CTV-specific rules matter because connected-TV players are less forgiving than desktop tooling. Wrapper depth, media formats, and measurement integrations tend to fail there first. Affected scope: VAST 4.1, 4.2, and 4.3.
How to fix
Add a <Mezzanine> element pointing to a high-quality source file (e.g. ProRes or high-bitrate H.264) so SSAI systems can transcode to the correct rendition.
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