# VTDecompressionSession An object that decompresses video data. ## Discussion A decompression session supports the decompression of a sequence of video frames. Here’s the basic workflow: 1. Create a decompression session by calling [`VTDecompressionSessionCreate(allocator:formatDescription:decoderSpecification:imageBufferAttributes:outputCallback:decompressionSessionOut:)`](/documentation/VideoToolbox/VTDecompressionSessionCreate(allocator:formatDescription:decoderSpecification:imageBufferAttributes:outputCallback:decompressionSessionOut:)). 2. Optionally, configure the session with your desired [Decompression Properties](/documentation/VideoToolbox/decompression-properties) by calling [`VTSessionSetProperty(_:key:value:)`](/documentation/VideoToolbox/VTSessionSetProperty(_:key:value:)) or [`VTSessionSetProperties(_:propertyDictionary:)`](/documentation/VideoToolbox/VTSessionSetProperties(_:propertyDictionary:)). 3. Decode video frames using [`VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:frameRefcon:infoFlagsOut:)`](/documentation/VideoToolbox/VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:frameRefcon:infoFlagsOut:)). 4. When you finish with the decompression session, call [`VTDecompressionSessionInvalidate(_:)`](/documentation/VideoToolbox/VTDecompressionSessionInvalidate(_:)) to tear it down, and call to free its memory. ## Topics ### Creating a Session [`func VTDecompressionSessionCreate(allocator: CFAllocator?, formatDescription: CMVideoFormatDescription, decoderSpecification: CFDictionary?, imageBufferAttributes: CFDictionary?, decompressionSessionOut: UnsafeMutablePointer) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionCreate(allocator:formatDescription:decoderSpecification:imageBufferAttributes:decompressionSessionOut:)) [`func VTDecompressionSessionCreate(allocator: CFAllocator?, formatDescription: CMVideoFormatDescription, decoderSpecification: CFDictionary?, imageBufferAttributes: CFDictionary?, outputCallback: UnsafePointer?, decompressionSessionOut: UnsafeMutablePointer) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionCreate(allocator:formatDescription:decoderSpecification:imageBufferAttributes:outputCallback:decompressionSessionOut:)) Creates a session for decompressing video frames. ### Configuring a Session [Decompression Properties](/documentation/VideoToolbox/decompression-properties) Properties used to configure a VideoToolbox decompression session. [`func VTVideoDecoderExtensionProperties(CMFormatDescription) throws -> [VTExtensionPropertiesKey : Any]`](/documentation/VideoToolbox/VTVideoDecoderExtensionProperties(_:)) ### Decoding Frames [`func VTDecompressionSessionCanAcceptFormatDescription(VTDecompressionSession, formatDescription: CMFormatDescription) -> Bool`](/documentation/VideoToolbox/VTDecompressionSessionCanAcceptFormatDescription(_:formatDescription:)) Indicates whether the session can decode frames with the given format description. [`func VTDecompressionSessionDecodeFrame(VTDecompressionSession, sampleBuffer: CMSampleBuffer, flags: VTDecodeFrameFlags, frameRefcon: UnsafeMutableRawPointer?, infoFlagsOut: UnsafeMutablePointer?) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:frameRefcon:infoFlagsOut:)) Decompresses a video frame. [`func VTDecompressionSessionDecodeFrame(VTDecompressionSession, sampleBuffer: CMSampleBuffer, flags: VTDecodeFrameFlags, frameOptions: CFDictionary?, frameRefcon: UnsafeMutableRawPointer?, infoFlagsOut: UnsafeMutablePointer?) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:frameOptions:frameRefcon:infoFlagsOut:)) [`func VTDecompressionSessionDecodeFrame(VTDecompressionSession, sampleBuffer: CMSampleBuffer, flags: VTDecodeFrameFlags, infoFlagsOut: UnsafeMutablePointer?, outputHandler: VTDecompressionOutputHandler) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:infoFlagsOut:outputHandler:)) Decompresses a video frame and invokes the output callback when the decompression completes. [`func VTDecompressionSessionDecodeFrame(VTDecompressionSession, sampleBuffer: CMSampleBuffer, flags: VTDecodeFrameFlags, frameOptions: CFDictionary?, infoFlagsOut: UnsafeMutablePointer?, outputHandler: VTDecompressionOutputHandler) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:frameOptions:infoFlagsOut:outputHandler:)) [`func VTDecompressionSessionDecodeFrame(VTDecompressionSession, sampleBuffer: CMSampleBuffer, flags: VTDecodeFrameFlags, infoFlagsOut: UnsafeMutablePointer?, completionHandler: (OSStatus, VTDecodeInfoFlags, CVImageBuffer?, [CMTaggedBuffer]?, CMTime, CMTime) -> Void) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionDecodeFrame(_:sampleBuffer:flags:infoFlagsOut:completionHandler:)) Decompresses a video frame and calls the provided output closure when decompression completes. [`func VTDecompressionSessionFinishDelayedFrames(VTDecompressionSession) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionFinishDelayedFrames(_:)) Directs the decompression session to emit all delayed frames. [`func VTDecompressionSessionWaitForAsynchronousFrames(VTDecompressionSession) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionWaitForAsynchronousFrames(_:)) Waits for any and all outstanding asynchronous and delayed frames to complete, then returns. [`func VTDecompressionSessionCopyBlackPixelBuffer(VTDecompressionSession, pixelBufferOut: UnsafeMutablePointer) -> OSStatus`](/documentation/VideoToolbox/VTDecompressionSessionCopyBlackPixelBuffer(_:pixelBufferOut:)) Copies a black pixel buffer from the decompression session. ### Decoding Multi-Image Frames [`func VTIsStereoMVHEVCDecodeSupported() -> Bool`](/documentation/VideoToolbox/VTIsStereoMVHEVCDecodeSupported()) Returns a Boolean value that indicates whether the system supports MV-HEVC decoding. [`extern OSStatus VTDecompressionSessionSetMultiImageCallback(VTDecompressionSessionRef decompressionSession, VTDecompressionOutputMultiImageCallback outputMultiImageCallback, void *outputMultiImageRefcon);`](/documentation/VideoToolbox/VTDecompressionSessionSetMultiImageCallback) Provides a callback capable of receiving multiple images for individual frame decoding requests. [`extern OSStatus VTDecompressionSessionDecodeFrameWithMultiImageCapableOutputHandler(VTDecompressionSessionRef session, CMSampleBufferRef sampleBuffer, VTDecodeFrameFlags decodeFlags, VTDecodeInfoFlags *infoFlagsOut, VTDecompressionMultiImageCapableOutputHandler multiImageCapableOutputHandler);`](/documentation/VideoToolbox/VTDecompressionSessionDecodeFrameWithMultiImageCapableOutputHandler) Decompresses a multi-image frame and calls the specified output handler upon completion. [`typealias VTDecompressionMultiImageCapableOutputHandler`](/documentation/VideoToolbox/VTDecompressionMultiImageCapableOutputHandler) A type alias for callback that the system invokes when it finishes decompressing a frame. ### Invalidating a Session [`func VTDecompressionSessionInvalidate(VTDecompressionSession)`](/documentation/VideoToolbox/VTDecompressionSessionInvalidate(_:)) Tears down a decompression session. ### Accessing the Type Identifier [`func VTDecompressionSessionGetTypeID() -> CFTypeID`](/documentation/VideoToolbox/VTDecompressionSessionGetTypeID()) Returns the Core Foundation type identifier for the decompression session. ### Data Types [`class VTDecompressionSession`](/documentation/VideoToolbox/VTDecompressionSession) A reference to a decompression session. [`struct VTDecodeFrameFlags`](/documentation/VideoToolbox/VTDecodeFrameFlags) Flags to pass to a decompression session and the video decoder. [`struct VTDecodeInfoFlags`](/documentation/VideoToolbox/VTDecodeInfoFlags) Flags that provide information about the status of a decode operation. [`typealias VTDecompressionOutputCallback`](/documentation/VideoToolbox/VTDecompressionOutputCallback) The prototype for the callback invoked when frame decompression is complete. [`struct VTDecompressionOutputCallbackRecord`](/documentation/VideoToolbox/VTDecompressionOutputCallbackRecord) [`typealias VTDecompressionOutputHandler`](/documentation/VideoToolbox/VTDecompressionOutputHandler) The prototype for the block invoked when frame decompression is complete. --- 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)