What does HRESULT 0x80040234 (VFW_E_ALREADY_CANCELLED) mean?

VFW_E_ALREADY_CANCELLED

Meaning

Windows documents VFW_E_ALREADY_CANCELLED as “The queued command has already been canceled”. In practical terms, it is returned when a DirectShow queued command or advise request has already been canceled when code attempts to cancel it again.

Likely causes

• Possible cause 1: two owners call cancel for the same token.
• Possible cause 2: timeout cleanup races normal completion cleanup.
• Possible cause 3: a stale command handle is reused after cancellation.

Evidence to collect

• Capture 1: command or advise token and owning component.
• Capture 2: first successful cancellation timestamp and thread.
• Capture 3: completion callback and cleanup call order.

Correct handling and retry

• Corrective action 1: make cancellation idempotent in the application layer.
• Corrective action 2: transfer token ownership explicitly.
• Corrective action 3: clear handles after completion or cancellation.

Retry guidance. Do not retry cancellation; treat the token as terminal and continue cleanup.

Practical scenario

A timeout thread and UI stop handler both cancel the same advise cookie; single-owner cleanup prevents it.

Difference from nearby HRESULTs

VFW_E_NO_ADVISE_SET means no successful advise existed, while it means an existing queued operation was already canceled.

Official Microsoft references

• Microsoft: DirectShow error and success codes
• Microsoft: IOverlay::Advise
• Microsoft: DirectShow reference clocks