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VFW_E_UNKNOWN_FILE_TYPE
Meaning
Windows documents VFW_E_UNKNOWN_FILE_TYPE as “The media type of this file is not recognized”. In practical terms, it is returned when DirectShow graph building cannot recognize the media type or select a source filter for the supplied file.
Where the failure belongs
This result belongs to DirectShow filter-graph processing. The relevant condition is that DirectShow graph building cannot recognize the media type or select a source filter for the supplied file.
Evidence to collect
- Capture 1: file signature and extension.
- Capture 2: source-filter enumeration and registration.
- Capture 3: IGraphBuilder::RenderFile result before fallback handlers.
Likely causes
- Possible cause 1: the file signature is unknown to registered source filters.
- Possible cause 2: the extension is misleading and no byte-pattern match succeeds.
- Possible cause 3: the required source filter is not installed or registered.
Diagnostic sequence
- Confirm that the observed path matches this condition: DirectShow graph building cannot recognize the media type or select a source filter for the supplied file.
Practical scenario
A proprietary container is renamed with a common extension but no registered filter recognizes its signature; installing the correct source filter resolves it.
Correct handling and retry
- Corrective action 1: identify the actual container format.
- Corrective action 2: install a supported source filter or use Media Foundation where appropriate.
- Corrective action 3: avoid trusting extension alone.
Retry guidance. Retry after changing the file, source-filter registration or explicit source selection.
Difference from nearby HRESULTs
VFW_E_INVALID_FILE_FORMAT means a format was selected but its structure is invalid; it means DirectShow cannot identify the type.
Official Microsoft references
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