---
title: kVTCompressionPropertyKey_SourceFrameCount
framework: videotoolbox
role: symbol
role_heading: Global Variable
path: videotoolbox/kvtcompressionpropertykey_sourceframecount
---

# kVTCompressionPropertyKey_SourceFrameCount

The number of source frames, if known.

## Declaration

```swift
let kVTCompressionPropertyKey_SourceFrameCount: CFString
```

## Discussion

Discussion This property allows a client to give the video encoder advance guidance as to how many frames will be encoded. If nonzero, this value should be the exact number of times that the client calls VTCompressionSessionEncodeFrame(_:imageBuffer:presentationTimeStamp:duration:frameProperties:sourceFrameRefcon:infoFlagsOut:) in each pass. The default is 0, which indicates that the number of source frames is unknown.

## See Also

### Encoding Hints

- [kVTCompressionPropertyKey_ExpectedDuration](videotoolbox/kvtcompressionpropertykey_expectedduration.md)
- [kVTCompressionPropertyKey_ExpectedFrameRate](videotoolbox/kvtcompressionpropertykey_expectedframerate.md)
- [kVTCompressionPropertyKey_MaximumRealTimeFrameRate](videotoolbox/kvtcompressionpropertykey_maximumrealtimeframerate.md)
- [kVTCompressionPropertyKey_PrioritizeEncodingSpeedOverQuality](videotoolbox/kvtcompressionpropertykey_prioritizeencodingspeedoverquality.md)
- [kVTCompressionPropertyKey_ReferenceBufferCount](videotoolbox/kvtcompressionpropertykey_referencebuffercount.md)
- [kVTCompressionPropertyKey_SuggestedLookAheadFrameCount](videotoolbox/kvtcompressionpropertykey_suggestedlookaheadframecount.md)