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WINCODEC_ERR_DUPLICATEMETADATAPRESENT
Metadata containers can legally hold repeated block types
WINCODEC_ERR_DUPLICATEMETADATAPRESENT is raised when duplicate metadata prevents WIC from selecting a unique item or block for the requested operation. Image containers can contain several metadata readers of the same broad format, and query paths may need an index or a more specific schema expression to distinguish them. A generic EXIF, XMP, or IFD request can therefore be ambiguous even though each block is individually parseable.
Deduplicating by deleting the first block is risky because repeated blocks can carry different namespaces or frame-level data. Enumerate the metadata block reader, inspect each handler’s format and location, then choose the target defined by the container and application policy. Re-encoding can also consolidate metadata, but it may discard unknown blocks unless they are deliberately copied.
Resolving ambiguity safely
- Enumerate all metadata blocks at the decoder or frame level before writing.
- Use indexed query expressions when the same block schema appears more than once.
- Compare payloads and namespaces rather than assuming duplicate type means duplicate content.
- Preserve unknown metadata explicitly during any decode-and-re-encode fallback.
References
- Microsoft: WIC metadata block model
- Microsoft: reading and writing image metadata
- Microsoft: metadata query path expressions
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