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# streamSinkBufferUnderrunCount

A property key for the buffer underrun count.

```
static let streamSinkBufferUnderrunCount: CMIOExtensionProperty
```

## Discussion

The system updates this value every time you don’t service a stream’s buffer fast enough.

The property state for property is a number with a read-only attribute. The value of this property matches the value of the [`kCMIOStreamPropertyOutputBufferUnderrunCount`](/documentation/CoreMediaIO/kCMIOStreamPropertyOutputBufferUnderrunCount) property.

---

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