# kVTCompressionPropertyKey_RecommendedParallelizationLimit The recommended number of compression sessions to instantiate in a parallel encoding configuration. ``` let kVTCompressionPropertyKey_RecommendedParallelizationLimit: CFString ``` ## Discussion Configuring a compression session for parallel encoding requires the use of the [`kVTCompressionPropertyKey_MoreFramesBeforeStart`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesBeforeStart), [`kVTCompressionPropertyKey_MoreFramesAfterEnd`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesAfterEnd), and [`kVTCompressionPropertyKey_SourceFrameCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SourceFrameCount) properties. For example, if the recommended parallelization limit is 4, a setup for 4 compression sessions for a 400 frame movie might look like the following: - **Compression Session 1**: [`kVTCompressionPropertyKey_MoreFramesBeforeStart`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesBeforeStart) `= false` [`kVTCompressionPropertyKey_MoreFramesAfterEnd`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesAfterEnd) `= true` [`kVTCompressionPropertyKey_SourceFrameCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SourceFrameCount) `= 100` - **Compression Session 2**: [`kVTCompressionPropertyKey_MoreFramesBeforeStart`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesBeforeStart) `= true` [`kVTCompressionPropertyKey_MoreFramesAfterEnd`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesAfterEnd) `= true` [`kVTCompressionPropertyKey_SourceFrameCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SourceFrameCount) `= 100` - **Compression Session 3**: [`kVTCompressionPropertyKey_MoreFramesBeforeStart`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesBeforeStart) `= true` [`kVTCompressionPropertyKey_MoreFramesAfterEnd`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesAfterEnd) `= true` [`kVTCompressionPropertyKey_SourceFrameCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SourceFrameCount) `= 100` - **Compression Session 4**: [`kVTCompressionPropertyKey_MoreFramesBeforeStart`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesBeforeStart) `= true` [`kVTCompressionPropertyKey_MoreFramesAfterEnd`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesAfterEnd) `= false` [`kVTCompressionPropertyKey_SourceFrameCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SourceFrameCount) `= 100` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)