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# validateCaptionConversion(warningHandler:)

Validates the object’s captions.

```
func validateCaptionConversion(warningHandler handler: @escaping @Sendable (AVCaptionConversionWarning?) -> Void)
```

## Parameters

`handler`

The callback the system invokes when it finishes validation.

## Discussion

When the object finishes validating and reports all warnings, it invokes the callback once with a value of `nil` for its warning parameter. When this occurs, the validator’s [`status`](/documentation/AVFoundation/AVCaptionConversionValidator/status-swift.property) value changes to [`AVCaptionConversionValidator.Status.completed`](/documentation/AVFoundation/AVCaptionConversionValidator/Status-swift.enum/completed).

Stop an in-progress validation operation by calling [`stopValidating()`](/documentation/AVFoundation/AVCaptionConversionValidator/stopValidating()).

> Important:
> It’s only valid to call this method when the validator’s state is ``doc://com.apple.avfoundation/documentation/AVFoundation/AVCaptionConversionValidator/Status-swift.enum/unknown``.

---

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