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# VTDecompressionOutputMultiImageCallback

A callback that the system invokes when multi-image frame decompression completes.

```
typealias VTDecompressionOutputMultiImageCallback = (UnsafeMutableRawPointer?, UnsafeMutableRawPointer?, OSStatus, VTDecodeInfoFlags, __CMTaggedBufferGroup?, CMTime, CMTime) -> Void
```

## Parameters

`decompressionOutputMultiImageRefCon`

The callback’s reference value, copied from the `outputMultiImageRefcon` argument passed to [`VTDecompressionSessionSetMultiImageCallback`](/documentation/VideoToolbox/VTDecompressionSessionSetMultiImageCallback).

`sourceFrameRefCon`

The frame’s reference value, copied from the `sourceFrameRefCon` argument passed to [`VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:frameRefcon:infoFlagsOut:)`](/documentation/VideoToolbox/VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:frameRefcon:infoFlagsOut:)).

`status`

A value of `noErr` if decompression succeeds or an error code if decompression fails.

`infoFlags`

Contains information about the decode operation:

- An [`asynchronous`](/documentation/VideoToolbox/VTDecodeInfoFlags/asynchronous) flag indicates the decode ran asynchronously.
- A [`frameDropped`](/documentation/VideoToolbox/VTDecodeInfoFlags/frameDropped) flag indicates the session dropped a frame.
- An [`imageBufferModifiable`](/documentation/VideoToolbox/VTDecodeInfoFlags/imageBufferModifiable) flag indicates that you can safely modify the image buffer.

`taggedBufferGroup`

Contains the decompressed frame’s multiple images, if decompression was successful; otherwise, `NULL`.

`presentationTimeStamp`

The frame’s presentation timestamp, which the system determines by calling <doc://com.apple.documentation/documentation/CoreMedia/CMSampleBufferGetOutputPresentationTimeStamp(_:)>; otherwise, <doc://com.apple.documentation/documentation/CoreMedia/CMTime/invalid> if the timestamp isn’t available.

`presentationDuration`

The frame’s presentation duration, which the system determines by calling <doc://com.apple.documentation/documentation/CoreMedia/CMSampleBufferGetOutputDuration(_:)>; otherwise, <doc://com.apple.documentation/documentation/CoreMedia/CMTime/invalid> if the duration isn’t available.

## Discussion

The system doesn’t guarantee that it calls this function in display order.

> Important:
> The video decompressor may still reference the pixel buffers returned in this callback if the ``doc://com.apple.videotoolbox/documentation/VideoToolbox/VTDecodeInfoFlags/imageBufferModifiable`` flag isn’t set. It’s not safe to modify the image buffer in this state.

---

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