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# QCCompositionProtocolMusicVisualizer

A  composition that acts as a visualizer for music.  A conforming composition must use the input key [`QCCompositionInputAudioPeakKey`](/documentation/Quartz/QCCompositionInputAudioPeakKey) for the instantaneous audio peak and the [`QCCompositionInputAudioSpectrumKey`](/documentation/Quartz/QCCompositionInputAudioSpectrumKey)  for the instantaneous audio spectrum. It can optionally use the [`QCCompositionInputTrackInfoKey`](/documentation/Quartz/QCCompositionInputTrackInfoKey) to indicate it receives information about the current  track and the [`QCCompositionInputTrackSignalKey`](/documentation/Quartz/QCCompositionInputTrackSignalKey) to indicate the start of a new track.

```
let QCCompositionProtocolMusicVisualizer: String
```

---

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