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VFW_E_READ_ONLY
Exact result and bit fields
VFW_E_READ_ONLY has the unsigned HRESULT value 2147746402 (0x80040262) and the signed 32-bit representation -2147220894. AllStat describes it as “The connection cannot be made because the stream is read only and the filter alters the data”. In the operation that produces this result, DirectShow refuses a connection because the upstream stream is read-only while the downstream filter would modify sample data in place.
The high bit is set, so this value is a failure HRESULT. Its facility field is 4 (FACILITY_ITF) and its low code is 610 (0x0262). 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.
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: pin interfaces and transport type.
- Evidence 2 for it: allocator properties and sample read-only flags.
- Evidence 3 for it: which filter intends to modify the buffer.
Conditions that can produce it
- Cause 1 for it: the downstream transform declares writable-buffer requirements.
- Cause 2 for it: a source exposes immutable shared memory.
- Cause 3 for it: allocator negotiation fails to provide copy-on-write samples.
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 refuses a connection because the upstream stream is read-only while the downstream filter would modify sample data in place.
- 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.
Retry and recovery
Retry rule for it: Retry after changing the transport or filter chain so writable storage is available. 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.
Correction strategy
- Action 1 for it: insert a copying transform or choose a non-mutating filter.
- Action 2 for it: negotiate an allocator that provides writable samples.
- Action 3 for it: declare in-place modification requirements accurately.
Example incident
A parser exposes read-only mapped-file samples to an in-place watermark filter; inserting a copy transform 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.
How it differs from nearby results
VFW_E_NO_TRANSPORT means pins share no transport mechanism, while it means transport exists but its mutability contract conflicts with the filter. Keep those cases separate in telemetry, UI messages and retry policy because their next actions are different.
Official Microsoft references
- Microsoft: DirectShow error and success codes
- Microsoft: media samples and allocators
- Microsoft: DirectShow filters and pins
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