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Error catalogue

afmpeg standardises on a single error library — cockroachdb/errors — for creation and wrapping, with user-facing hints where useful. Every exported sentinel error (var ErrX = errors.New(...) in pkg/) is documented here; this is enforced advisorily by scripts/lint-docs-errors.sh (the just check target), which fails if a sentinel in pkg/ is missing from this page.

Sentinels

ErrNoModule

Returned by afmpeg.New when no wasm module source is configured. The GPL ffmpeg.wasm is never embedded (spec 0004 D-C), so one of WithModuleFile, WithModuleBytes, WithModuleFS, or WithModuleURL is mandatory. Callers match with errors.Is(err, afmpeg.ErrNoModule).

ErrChecksumMismatch

Returned when a module obtained via WithModuleURL + WithSHA256 does not match the expected SHA-256 — the download is rejected rather than executed. Callers match with errors.Is(err, afmpeg.ErrChecksumMismatch).

Convention

  • A non-zero ffmpeg exit is not a Go error by itself — Run returns a Result carrying the exit code + stderr tail, and a nil error. Host-side failures (module instantiation, the vfs bridge, context cancellation) return a non-nil error. A consumer that prefers an error on failure inspects Result.ExitCode and wraps it with the stderr tail itself.
  • Wrap, don't reformat: errors.Wrap/Wrapf to add context; reserve sentinels for conditions callers branch on.