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# VTRAWProcessingSessionSetParameterChangedHander

Provides a block which will be called when the session changes the set of processing parameters.

```
extern OSStatus VTRAWProcessingSessionSetParameterChangedHander(VTRAWProcessingSessionRef session, VTRAWProcessingParameterChangeHandler parameterChangeHandler);
```

## Parameters

`session`

The RAW processing session.

`parameterChangeHandler`

A [`VTRAWProcessingParameterChangeHandler`](/documentation/VideoToolbox/VTRAWProcessingParameterChangeHandler) block which will be called when the set of processing parameters changes, or the value of a parameter changes without the client explicitly requesting it. Setting this to `NULL` removes the current handler.

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