---
title: kVTCompressionPropertyKey_VariableBitRate
framework: videotoolbox
role: symbol
role_heading: Global Variable
path: videotoolbox/kvtcompressionpropertykey_variablebitrate
---

# kVTCompressionPropertyKey_VariableBitRate

## Declaration

```swift
let kVTCompressionPropertyKey_VariableBitRate: CFString
```

## Discussion

Discussion Requires that the encoder use a variable bitrate (VBR) rate control algorithm and specifies the desired variable bitrate in bits per second. The actual peak bitrate present in the bitstream may be above or below this value based on other parameters such as kVTCompressionPropertyKey_VBVMaxBitRate. This property key needs to be set to achieve Variable Bitrate (VBR) rate control. This property key is not compatible with: kVTCompressionPropertyKey_AverageBitRate, kVTCompressionPropertyKey_ConstantBitRate, kVTCompressionPropertyKey_DataRateLimits, VTVideoEncoderSpecification_EnableLowLatencyRateControl = True.

## See Also

### Rate Control

- [kVTCompressionPropertyKey_AverageBitRate](videotoolbox/kvtcompressionpropertykey_averagebitrate.md)
- [kVTCompressionPropertyKey_ConstantBitRate](videotoolbox/kvtcompressionpropertykey_constantbitrate.md)
- [kVTCompressionPropertyKey_DataRateLimits](videotoolbox/kvtcompressionpropertykey_dataratelimits.md)
- [kVTCompressionPropertyKey_EstimatedAverageBytesPerFrame](videotoolbox/kvtcompressionpropertykey_estimatedaveragebytesperframe.md)
- [kVTCompressionPropertyKey_MoreFramesAfterEnd](videotoolbox/kvtcompressionpropertykey_moreframesafterend.md)
- [kVTCompressionPropertyKey_MoreFramesBeforeStart](videotoolbox/kvtcompressionpropertykey_moreframesbeforestart.md)
- [kVTCompressionPropertyKey_Quality](videotoolbox/kvtcompressionpropertykey_quality.md)
- [kVTCompressionPropertyKey_TargetQualityForAlpha](videotoolbox/kvtcompressionpropertykey_targetqualityforalpha.md)
- [kVTCompressionPropertyKey_VBVBufferDuration](videotoolbox/kvtcompressionpropertykey_vbvbufferduration.md)
- [kVTCompressionPropertyKey_VBVInitialDelayPercentage](videotoolbox/kvtcompressionpropertykey_vbvinitialdelaypercentage.md)
- [kVTCompressionPropertyKey_VBVMaxBitRate](videotoolbox/kvtcompressionpropertykey_vbvmaxbitrate.md)