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# kAudioFilePropertyMagicCookieData

A pointer to memory set up by the caller. Some file types require that a magic cookie be provided before packets can be written to an audio file. Set this property before you call [`AudioFileWriteBytes(_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileWriteBytes(_:_:_:_:_:)) or [`AudioFileWritePackets(_:_:_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileWritePackets(_:_:_:_:_:_:_:)) if a magic cookie exists.

```
var kAudioFilePropertyMagicCookieData: AudioFilePropertyID { get }
```

---

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