---
title: VTCompressionOutputCallback
framework: videotoolbox
role: symbol
role_heading: Type Alias
path: videotoolbox/vtcompressionoutputcallback
---

# VTCompressionOutputCallback

A callback for the system to invoke when it’s finished compressing a frame.

## Declaration

```swift
typealias VTCompressionOutputCallback = (UnsafeMutableRawPointer?, UnsafeMutableRawPointer?, OSStatus, VTEncodeInfoFlags, CMSampleBuffer?) -> Void
```

## Parameters

- `outputCallbackRefCon`: The callback’s reference value.
- `sourceFrameRefCon`: The frame’s reference value, copied from the sourceFrameRefCon argument to doc://com.apple.videotoolbox/documentation/VideoToolbox/VTCompressionSessionEncodeFrame(_:imageBuffer:presentationTimeStamp:duration:frameProperties:sourceFrameRefcon:infoFlagsOut:).
- `status`: noErr if compression was successful; an error code if compression wasn’t successful.
- `infoFlags`: Contains information about the encode operation. The doc://com.apple.videotoolbox/documentation/VideoToolbox/VTEncodeInfoFlags/asynchronous bit may be set if the encode ran asynchronously. The doc://com.apple.videotoolbox/documentation/VideoToolbox/VTEncodeInfoFlags/frameDropped bit may be set if the frame was dropped.
- `sampleBuffer`: Contains the compressed frame if compression was successful and the frame wasn’t dropped; otherwise, NULL.

## Discussion

Discussion When you create a compression session, you pass in a callback function to be called for compressed frames.  This function is called in decode order (which is not necessarily the same as display order).

## See Also

### Callbacks

- [VTCompressionOutputHandler](videotoolbox/vtcompressionoutputhandler.md)