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VFW_E_BAD_KEY
Exact result and bit fields
VFW_E_BAD_KEY has the unsigned HRESULT value 2147746802 (0x800403F2) and the signed 32-bit representation -2147220494. AllStat describes it as “A registry entry is corrupt”. In the operation that produces this result, DirectShow reads a registry entry used for filter or media configuration and finds corrupt or unusable data.
The high bit is set, so this value is a failure HRESULT. Its facility field is 4 (FACILITY_ITF) and its low code is 1010 (0x03F2). These fields classify this result, but they do not identify which filter, thread, device, file or graph generation returned it.
Contract boundary
This result is a DirectShow contract failure whose owner must be identified from the exact interface, filter instance, graph generation and operation stage.
The practical owner to locate for it is the filter graph, device or persisted configuration that first returned the result. When handling this result, capture the native result before a wrapper replaces it with a generic exception, and keep the graph generation or object identity with the record.
Step-by-step diagnosis
- Capture it at the first native return, not only at the top-level playback failure.
- identify the exact graph stage described here: DirectShow reads a registry entry used for filter or media configuration and finds corrupt or unusable data.
- compare the live object state, topology and input with the documented interface preconditions.
- Before changing filters, drivers, registry data or media for it, collect the code-specific evidence below.
- Test one evidence-backed the correction on the smallest reproducible graph.
- Verify that the corrected run no longer returns it and does not merely replace it with a nearby HRESULT.
Conditions that can produce it
- Cause 1 for it: a filter-registration value was partially written.
- Cause 2 for it: manual registry editing produced an invalid type or payload.
- Cause 3 for it: an obsolete component left incompatible data behind.
Evidence worth preserving
Log the interface and method, filter CLSID and friendly name, process and thread, graph state, connected pin names, media-type summary, renderer or device identity where relevant, and the first preceding HRESULT. Record lengths and hashes instead of raw content when the incident includes media paths, device identifiers, registry values and stream metadata.
- Evidence 1 for it: registry path, value name, type and size.
- Evidence 2 for it: component installer and version owning the key.
- Evidence 3 for it: comparison with a clean installation of the same build.
Correction strategy
- Action 1 for it: repair the component through its supported installer.
- Action 2 for it: validate registry data before interpreting it.
- Action 3 for it: remove only entries proven to belong to the broken registration and preserve a backup.
Retry and recovery
Retry rule for it: Retry after supported repair or verified registry correction; repeated reads of the same corrupt value cannot succeed. A safe it retry must use a changed capability, state, object generation or input. While recovering from it, preserve cancellation and avoid replaying side effects when the original operation may have partially completed.
How it differs from nearby results
REGDB_E_INVALIDVALUE is a general COM registration database result, while it identifies corrupt registry data encountered by a DirectShow path. Keep those cases separate in telemetry, UI messages and retry policy because their next actions are different.
Example incident
A filter installer crashes while updating registration metadata and leaves a truncated binary value; reinstalling that component resolves it. This example keeps the diagnosis at the specific the boundary instead of treating every DirectShow failure as a codec reinstall problem.
Implementation notes
Code that handles it should preserve the original HRESULT, the failed stage and an opaque correlation identifier. After it, do not infer success from partial graph construction, and do not continue using interfaces retained from a graph or device generation that has already changed.
Operational remediation for it should favor supported component installation, device configuration and documented DirectShow calls. Manual registry or driver changes are appropriate only when the collected evidence for it points to that layer and a rollback is available.
Official Microsoft references
- Microsoft: DirectShow error and success codes
- Microsoft: using the Filter Mapper
- Microsoft: DirectShow filters and pins
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