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VFW_S_NOPREVIEWPIN
Capture graph provides preview by splitting the capture stream
VFW_S_NOPREVIEWPIN is HRESULT 262782 (0x0004027E) from Video for Windows. AllStat describes this result as “There was no preview pin available, so the capture pin output is being split to provide both capture and preview.” The high-order severity bit is clear, so this is a success result, but it carries more information than plain S_OK.
No dedicated preview pin was available, so graph building created preview behavior by splitting the capture-pin output.
Where the result is encountered
- This result can appear in ICaptureGraphBuilder2 preview construction; record the producing interface and method rather than inferring behavior from the symbolic name alone.
- This result can appear in capture devices exposing only a capture pin; record the producing interface and method rather than inferring behavior from the symbolic name alone.
- It can appear in applications requesting simultaneous preview and recording; record the producing interface and method rather than inferring behavior from the symbolic name alone.
The same numeric success value can be mishandled when a wrapper exposes only a Boolean. Keep the original HRESULT until the code-specific outputs and state transition have been evaluated.
Diagnostic sequence
- capture the raw HRESULT
0x0004027Eimmediately after the returning method and record whether the caller usedSUCCEEDED,FAILED, equality testing, or exception translation. - Identify the exact owner of it: interface, method, object instance, provider or filter version, thread or apartment, and operation phase.
- Validate the decisive contract boundary for it: the inserted splitter path does not alter capture format, timing, or device performance beyond acceptable limits.
- inspect every output parameter, count, status array, returned interface, or side effect that the method documentation associates with this success-with-information result.
- Compare the observed state before and after it; do not assume that a success severity bit means every optional sub-operation completed.
- reproduce the smallest request with the same object state and then change only the condition identified by the evidence before repeating the operation.
State boundary that must be proved
The central question for it is whether the inserted splitter path does not alter capture format, timing, or device performance beyond acceptable limits. The HRESULT alone confirms neither unrelated work nor the quality of optional outputs.
A reliable interpretation of it names the exact method contract, the object generation, and the outputs that remain valid. This prevents a success-with-information result from being promoted to full success or demoted to a generic error.
Correct handling, retry, and recovery
Accept the synthesized preview when performance is adequate. If capture quality drops, disable preview or use hardware with a dedicated preview path instead of assuming the graph is equivalent.
Retry it only when the recorded state can change the documented outcome. Repeating the same call is inappropriate for a stable end marker, cancellation, unsupported format, adjusted property, or partial result whose completed side effects have not been reconciled.
Evidence and telemetry to preserve
- preserve device filter and pin categories.
- preserve resulting graph topology.
- preserve capture and preview media types.
- preserve CPU and dropped-frame metrics.
- preserve recorded output validation.
Also record vfw_s_nopreviewpin_operation, vfw_s_nopreviewpin_object, vfw_s_nopreviewpin_state_before, vfw_s_nopreviewpin_state_after, UTC time, process and thread identifiers, and a correlation ID. Keep secrets out of logs while retaining GUIDs, CLSIDs, media subtypes, property IDs, row identities, and hashes needed to distinguish objects.
Difference from nearby HRESULT values
S_OK may mean a real preview pin was used; it documents that preview was synthesized from capture output.
This distinction determines whether the caller should consume partial outputs, stop iteration, wait, reconfigure, notify the user, or perform no error recovery at all.
Developer and administrator guidance
When it crosses process, RPC, scripting, or managed-code boundaries, preserve the unsigned 32-bit value and symbolic name. A signed decimal rendering can obscure that the severity bit indicates success and can lead to incorrect exception or retry behavior.
A support report for it should include decimal 262782, hexadecimal 0x0004027E, the AllStat meaning, the owning API, and the first detailed status or output that explains why the method did not return ordinary S_OK.
Practical validation scenario
A USB camera exposes only PIN_CATEGORY_CAPTURE. The capture graph builder inserts a splitter for preview; testing confirms the recorded stream keeps its expected frame rate under preview load.
The negative test should preserve the condition that produces it; the recovery test should alter only that condition and verify the final state as well as the HRESULT.
References
- Microsoft: DirectShow error and success codes
- Microsoft: DirectShow overview
- Microsoft: Capture Graph Builder
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