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# VTCompressionSessionPrepareToEncodeFrames(_:)

Enables the encoder to perform any necessary resource allocation before the encoder begins encoding frames (optional).

```
func VTCompressionSessionPrepareToEncodeFrames(_ session: VTCompressionSession) -> OSStatus
```

## Parameters

`session`

The compression session.

## Discussion

If this function isn’t called, any necessary resources are allocated on the first [`VTCompressionSessionEncodeFrame(_:imageBuffer:presentationTimeStamp:duration:frameProperties:sourceFrameRefcon:infoFlagsOut:)`](/documentation/VideoToolbox/VTCompressionSessionEncodeFrame(_:imageBuffer:presentationTimeStamp:duration:frameProperties:sourceFrameRefcon:infoFlagsOut:)) call.

Subsequent calls to this function have no effect.

---

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