# Compression Properties Properties that you use to configure a compression session. ## Discussion> Note: > Video encoders may not support all compression property keys. ## Topics ### Bitstream Configuration [`kVTCompressionPropertyKey_Depth`](/documentation/VideoToolbox/kVTCompressionPropertyKey_Depth) The pixel depth of the encoded video. [`kVTCompressionPropertyKey_H264EntropyMode`](/documentation/VideoToolbox/kVTCompressionPropertyKey_H264EntropyMode) The entropy encoding mode for H.264 compression. [`kVTCompressionPropertyKey_HDRMetadataInsertionMode`](/documentation/VideoToolbox/kVTCompressionPropertyKey_HDRMetadataInsertionMode) [`kVTCompressionPropertyKey_OutputBitDepth`](/documentation/VideoToolbox/kVTCompressionPropertyKey_OutputBitDepth) [`kVTCompressionPropertyKey_PreserveAlphaChannel`](/documentation/VideoToolbox/kVTCompressionPropertyKey_PreserveAlphaChannel) A key that specifies whether to encode the alpha channel of input video frames. [`kVTCompressionPropertyKey_PreserveDynamicHDRMetadata`](/documentation/VideoToolbox/kVTCompressionPropertyKey_PreserveDynamicHDRMetadata) Specifies whether to preserve dynamic HDR metadata on the input pixel buffer. [`kVTCompressionPropertyKey_ProfileLevel`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ProfileLevel) The profile and level for the encoded bitstream. ### Buffers [`kVTCompressionPropertyKey_NumberOfPendingFrames`](/documentation/VideoToolbox/kVTCompressionPropertyKey_NumberOfPendingFrames) The number of pending frames in the compression session. [`kVTCompressionPropertyKey_PixelBufferPoolIsShared`](/documentation/VideoToolbox/kVTCompressionPropertyKey_PixelBufferPoolIsShared) A Boolean value indicating whether the common pixel buffer pool is shared between the video encoder and the session client. [`kVTCompressionPropertyKey_VideoEncoderPixelBufferAttributes`](/documentation/VideoToolbox/kVTCompressionPropertyKey_VideoEncoderPixelBufferAttributes) The video encoder’s pixel buffer attributes for the compression session. ### Camera Calibration [`kVTCompressionPropertyKey_CameraCalibrationDataLensCollection`](/documentation/VideoToolbox/kVTCompressionPropertyKey_CameraCalibrationDataLensCollection) [`kVTCompressionPropertyCameraCalibrationKey_ExtrinsicOrientationQuaternion`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_ExtrinsicOrientationQuaternion) [`kVTCompressionPropertyCameraCalibrationKey_ExtrinsicOriginSource`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_ExtrinsicOriginSource) [`kVTCompressionPropertyCameraCalibrationKey_IntrinsicMatrix`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_IntrinsicMatrix) [`kVTCompressionPropertyCameraCalibrationKey_IntrinsicMatrixProjectionOffset`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_IntrinsicMatrixProjectionOffset) [`kVTCompressionPropertyCameraCalibrationKey_IntrinsicMatrixReferenceDimensions`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_IntrinsicMatrixReferenceDimensions) [`kVTCompressionPropertyCameraCalibrationKey_LensAlgorithmKind`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_LensAlgorithmKind) [`kVTCompressionPropertyCameraCalibrationKey_LensDistortions`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_LensDistortions) [`kVTCompressionPropertyCameraCalibrationKey_LensDomain`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_LensDomain) [`kVTCompressionPropertyCameraCalibrationKey_LensFrameAdjustmentsPolynomialX`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_LensFrameAdjustmentsPolynomialX) [`kVTCompressionPropertyCameraCalibrationKey_LensFrameAdjustmentsPolynomialY`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_LensFrameAdjustmentsPolynomialY) [`kVTCompressionPropertyCameraCalibrationKey_LensIdentifier`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_LensIdentifier) [`kVTCompressionPropertyCameraCalibrationKey_LensRole`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_LensRole) [`kVTCompressionPropertyCameraCalibrationKey_RadialAngleLimit`](/documentation/VideoToolbox/kVTCompressionPropertyCameraCalibrationKey_RadialAngleLimit) ### Clean Aperture and Pixel Aspect Ratio [`kVTCompressionPropertyKey_AspectRatio16x9`](/documentation/VideoToolbox/kVTCompressionPropertyKey_AspectRatio16x9) A Boolean value indicating whether the DV video stream should have the 16x9 flag set. [`kVTCompressionPropertyKey_CleanAperture`](/documentation/VideoToolbox/kVTCompressionPropertyKey_CleanAperture) The clean aperture for encoded frames. [`kVTCompressionPropertyKey_FieldCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_FieldCount) The field count indicating whether the frames should be encoded progressive (1) or interlaced (2). [`kVTCompressionPropertyKey_FieldDetail`](/documentation/VideoToolbox/kVTCompressionPropertyKey_FieldDetail) Field ordering for encoded interlaced frames. [`kVTCompressionPropertyKey_PixelAspectRatio`](/documentation/VideoToolbox/kVTCompressionPropertyKey_PixelAspectRatio) The pixel aspect ratio for encoded frames. [`kVTCompressionPropertyKey_ProgressiveScan`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ProgressiveScan) A Boolean value indicating whether the DV video stream should have the progressive flag set. ### Color [`kVTCompressionPropertyKey_AlphaChannelMode`](/documentation/VideoToolbox/kVTCompressionPropertyKey_AlphaChannelMode) [`kVTCompressionPropertyKey_ColorPrimaries`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ColorPrimaries) The color primaries for compressed content. [`kVTCompressionPropertyKey_ContentLightLevelInfo`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ContentLightLevelInfo) [`kVTCompressionPropertyKey_GammaLevel`](/documentation/VideoToolbox/kVTCompressionPropertyKey_GammaLevel) [`kVTCompressionPropertyKey_ICCProfile`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ICCProfile) The ICC profile for compressed content. [`kVTCompressionPropertyKey_MasteringDisplayColorVolume`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MasteringDisplayColorVolume) [`kVTCompressionPropertyKey_TransferFunction`](/documentation/VideoToolbox/kVTCompressionPropertyKey_TransferFunction) The transfer function for compressed content. [`kVTCompressionPropertyKey_YCbCrMatrix`](/documentation/VideoToolbox/kVTCompressionPropertyKey_YCbCrMatrix) The YCbCr matrix for compressed content. ### Compression Presets [`kVTCompressionPreset_Balanced`](/documentation/VideoToolbox/kVTCompressionPreset_Balanced) [`kVTCompressionPreset_HighQuality`](/documentation/VideoToolbox/kVTCompressionPreset_HighQuality) [`kVTCompressionPreset_HighSpeed`](/documentation/VideoToolbox/kVTCompressionPreset_HighSpeed) [`kVTCompressionPreset_VideoConferencing`](/documentation/VideoToolbox/kVTCompressionPreset_VideoConferencing) [`kVTCompressionPropertyKey_SupportedPresetDictionaries`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SupportedPresetDictionaries) ### Encoder Selection [`kVTCompressionPropertyKey_EncoderID`](/documentation/VideoToolbox/kVTCompressionPropertyKey_EncoderID) Specifies a particular video encoder by its ID string. [`kVTVideoEncoderSpecification_EnableHardwareAcceleratedVideoEncoder`](/documentation/VideoToolbox/kVTVideoEncoderSpecification_EnableHardwareAcceleratedVideoEncoder) A Boolean value indicating whether hardware-accelerated video encoding is allowed, if available. [`kVTVideoEncoderSpecification_EnableLowLatencyRateControl`](/documentation/VideoToolbox/kVTVideoEncoderSpecification_EnableLowLatencyRateControl) Specifies to select an encoder that supports low-latency operation and enables low-latency mode. [`kVTVideoEncoderSpecification_EncoderID`](/documentation/VideoToolbox/kVTVideoEncoderSpecification_EncoderID) A key that indicates a particular video encoder to use. [`kVTVideoEncoderSpecification_PreferredEncoderGPURegistryID`](/documentation/VideoToolbox/kVTVideoEncoderSpecification_PreferredEncoderGPURegistryID) [`kVTVideoEncoderSpecification_RequiredEncoderGPURegistryID`](/documentation/VideoToolbox/kVTVideoEncoderSpecification_RequiredEncoderGPURegistryID) [`kVTVideoEncoderSpecification_RequireHardwareAcceleratedVideoEncoder`](/documentation/VideoToolbox/kVTVideoEncoderSpecification_RequireHardwareAcceleratedVideoEncoder) A Boolean value indicating whether hardware-accelerated encoding is required. ### Encoding Hints [`kVTCompressionPropertyKey_ExpectedDuration`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ExpectedDuration) The expected total duration of the compression session, if known. [`kVTCompressionPropertyKey_ExpectedFrameRate`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ExpectedFrameRate) The expected frame rate, if known. [`kVTCompressionPropertyKey_MaximumRealTimeFrameRate`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MaximumRealTimeFrameRate) A value that specifies the maximum real time rate at which frames can be submitted to a compression session. [`kVTCompressionPropertyKey_PrioritizeEncodingSpeedOverQuality`](/documentation/VideoToolbox/kVTCompressionPropertyKey_PrioritizeEncodingSpeedOverQuality) A hint for the video encoder to maximize its speed during encoding, sacrificing quality if needed. [`kVTCompressionPropertyKey_ReferenceBufferCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ReferenceBufferCount) [`kVTCompressionPropertyKey_SourceFrameCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SourceFrameCount) The number of source frames, if known. [`kVTCompressionPropertyKey_SuggestedLookAheadFrameCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SuggestedLookAheadFrameCount) A value that requests that the encoder retain the specified number of frames during encoding. ### Frame Dependency [`kVTCompressionPropertyKey_AllowFrameReordering`](/documentation/VideoToolbox/kVTCompressionPropertyKey_AllowFrameReordering) A Boolean value that indicates whether frame reordering is enabled. [`kVTCompressionPropertyKey_AllowOpenGOP`](/documentation/VideoToolbox/kVTCompressionPropertyKey_AllowOpenGOP) Enables Open GOP (Group Of Pictures) encoding. [`kVTCompressionPropertyKey_AllowTemporalCompression`](/documentation/VideoToolbox/kVTCompressionPropertyKey_AllowTemporalCompression) A Boolean value indicating whether temporal compression is enabled. [`kVTCompressionPropertyKey_MaxKeyFrameInterval`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MaxKeyFrameInterval) The maximum interval between key frames, also known as the key frame rate. [`kVTCompressionPropertyKey_MaxKeyFrameIntervalDuration`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MaxKeyFrameIntervalDuration) The maximum duration from one key frame to the next in seconds. ### Hardware Acceleration [`kVTCompressionPropertyKey_UsingGPURegistryID`](/documentation/VideoToolbox/kVTCompressionPropertyKey_UsingGPURegistryID) [`kVTCompressionPropertyKey_UsingHardwareAcceleratedVideoEncoder`](/documentation/VideoToolbox/kVTCompressionPropertyKey_UsingHardwareAcceleratedVideoEncoder) A Boolean value indicating whether a hardware-accelerated video encoder is used. ### Long-Term Reference [`kVTCompressionPropertyKey_EnableLTR`](/documentation/VideoToolbox/kVTCompressionPropertyKey_EnableLTR) Enables Long Term Reference (LTR) frames during encoding. [`kVTEncodeFrameOptionKey_AcknowledgedLTRTokens`](/documentation/VideoToolbox/kVTEncodeFrameOptionKey_AcknowledgedLTRTokens) Enable Long Term Reference (LTR) frames during encoding. [`kVTEncodeFrameOptionKey_ForceLTRRefresh`](/documentation/VideoToolbox/kVTEncodeFrameOptionKey_ForceLTRRefresh) A Boolean value that indicates whether to force Long Term Reference (LTR). [`kVTSampleAttachmentKey_RequireLTRAcknowledgementToken`](/documentation/VideoToolbox/kVTSampleAttachmentKey_RequireLTRAcknowledgementToken) A number value that contains a unique token for this Long Term Reference (LTR). ### Multipass Storage [`kVTCompressionPropertyKey_MultiPassStorage`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MultiPassStorage) A property key that enables multipass compression and provides storage for encoder private data. ### Multiview Compression [`kVTCompressionPropertyKey_MVHEVCLeftAndRightViewIDs`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MVHEVCLeftAndRightViewIDs) Specifies which view identifier corresponds to the left eye and right eye. [`kVTCompressionPropertyKey_MVHEVCVideoLayerIDs`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MVHEVCVideoLayerIDs) The identifiers of the video layers to encode in a multiview encoding operation. [`kVTCompressionPropertyKey_MVHEVCViewIDs`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MVHEVCViewIDs) The identifiers of the views corresponding to the video layers in a multiview encoding operation. ### Parallelization [`kVTCompressionPropertyKey_RecommendedParallelizationLimit`](/documentation/VideoToolbox/kVTCompressionPropertyKey_RecommendedParallelizationLimit) The recommended number of compression sessions to instantiate in a parallel encoding configuration. [`kVTCompressionPropertyKey_RecommendedParallelizedSubdivisionMinimumDuration`](/documentation/VideoToolbox/kVTCompressionPropertyKey_RecommendedParallelizedSubdivisionMinimumDuration) The recommended minimum duration for a given subdivision in a parallel encoding configuration. [`kVTCompressionPropertyKey_RecommendedParallelizedSubdivisionMinimumFrameCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_RecommendedParallelizedSubdivisionMinimumFrameCount) The recommended minimum number of video frames for a given subdivision in a parallel encoding configuration. ### Per-Frame Configuration [`kVTEncodeFrameOptionKey_BaseFrameQP`](/documentation/VideoToolbox/kVTEncodeFrameOptionKey_BaseFrameQP) [`kVTEncodeFrameOptionKey_ForceKeyFrame`](/documentation/VideoToolbox/kVTEncodeFrameOptionKey_ForceKeyFrame) Boolean value indicating whether the current frame is forced to be a key frame. ### Precompression Processing [`kVTCompressionPropertyKey_PixelTransferProperties`](/documentation/VideoToolbox/kVTCompressionPropertyKey_PixelTransferProperties) Properties for configuring a pixel transfer session. ### Quality Metrics [`kVTCompressionPropertyKey_CalculateMeanSquaredError`](/documentation/VideoToolbox/kVTCompressionPropertyKey_CalculateMeanSquaredError) [`kVTSampleAttachmentKey_QualityMetrics`](/documentation/VideoToolbox/kVTSampleAttachmentKey_QualityMetrics) [`kVTSampleAttachmentQualityMetricsKey_ChromaBlueMeanSquaredError`](/documentation/VideoToolbox/kVTSampleAttachmentQualityMetricsKey_ChromaBlueMeanSquaredError) [`kVTSampleAttachmentQualityMetricsKey_ChromaRedMeanSquaredError`](/documentation/VideoToolbox/kVTSampleAttachmentQualityMetricsKey_ChromaRedMeanSquaredError) [`kVTSampleAttachmentQualityMetricsKey_LumaMeanSquaredError`](/documentation/VideoToolbox/kVTSampleAttachmentQualityMetricsKey_LumaMeanSquaredError) ### Quantization [`kVTCompressionPropertyKey_MaxAllowedFrameQP`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MaxAllowedFrameQP) The maximum allowed encoded frame QP (Quantization Parameter). [`kVTCompressionPropertyKey_MinAllowedFrameQP`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MinAllowedFrameQP) The minimum allowed encoded frame QP (Quantization Parameter). [`kVTCompressionPropertyKey_SpatialAdaptiveQPLevel`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SpatialAdaptiveQPLevel) A value that controls spatial adaptation of the quantization parameter (QP) based on per-frame statistics. [`kVTCompressionPropertyKey_SupportsBaseFrameQP`](/documentation/VideoToolbox/kVTCompressionPropertyKey_SupportsBaseFrameQP) A value that indicates whether the encoder supports base frame QP requests. ### Rate Control [`kVTCompressionPropertyKey_AverageBitRate`](/documentation/VideoToolbox/kVTCompressionPropertyKey_AverageBitRate) The long-term desired average bit rate in bits per second. [`kVTCompressionPropertyKey_ConstantBitRate`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ConstantBitRate) Requires that the encoder use a Constant Bit Rate algorithm. [`kVTCompressionPropertyKey_DataRateLimits`](/documentation/VideoToolbox/kVTCompressionPropertyKey_DataRateLimits) Zero, one, or two hard limits on data rate. [`kVTCompressionPropertyKey_EstimatedAverageBytesPerFrame`](/documentation/VideoToolbox/kVTCompressionPropertyKey_EstimatedAverageBytesPerFrame) An estimate of the expected size in bytes of a single encoded frame based on the current configuration. [`kVTCompressionPropertyKey_MoreFramesAfterEnd`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesAfterEnd) A Boolean value indicating whether and how a compression session concatenates frames with other compressed frames to form a longer series. [`kVTCompressionPropertyKey_MoreFramesBeforeStart`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MoreFramesBeforeStart) A Boolean value that indicates whether and how a compression session concatenates frames with other compressed frames to form a longer series. [`kVTCompressionPropertyKey_Quality`](/documentation/VideoToolbox/kVTCompressionPropertyKey_Quality) The desired compression quality. [`kVTCompressionPropertyKey_TargetQualityForAlpha`](/documentation/VideoToolbox/kVTCompressionPropertyKey_TargetQualityForAlpha) The target quality to use for encoding the alpha channel. [`kVTCompressionPropertyKey_VariableBitRate`](/documentation/VideoToolbox/kVTCompressionPropertyKey_VariableBitRate) [`kVTCompressionPropertyKey_VBVBufferDuration`](/documentation/VideoToolbox/kVTCompressionPropertyKey_VBVBufferDuration) [`kVTCompressionPropertyKey_VBVInitialDelayPercentage`](/documentation/VideoToolbox/kVTCompressionPropertyKey_VBVInitialDelayPercentage) [`kVTCompressionPropertyKey_VBVMaxBitRate`](/documentation/VideoToolbox/kVTCompressionPropertyKey_VBVMaxBitRate) ### Runtime Restrictions [`kVTCompressionPropertyKey_MaxFrameDelayCount`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MaxFrameDelayCount) The maximum number of frames that a compressor is allowed to hold before it must output a compressed frame. [`kVTCompressionPropertyKey_MaxH264SliceBytes`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MaxH264SliceBytes) The maximum slice size for H.264 encoding. [`kVTCompressionPropertyKey_MaximizePowerEfficiency`](/documentation/VideoToolbox/kVTCompressionPropertyKey_MaximizePowerEfficiency) [`kVTCompressionPropertyKey_RealTime`](/documentation/VideoToolbox/kVTCompressionPropertyKey_RealTime) A Boolean value indicating whether it’s recommended that the video encoder perform compression in real time. ### Temporal Scalability [`kVTCompressionPropertyKey_BaseLayerBitRateFraction`](/documentation/VideoToolbox/kVTCompressionPropertyKey_BaseLayerBitRateFraction) [`kVTCompressionPropertyKey_BaseLayerFrameRate`](/documentation/VideoToolbox/kVTCompressionPropertyKey_BaseLayerFrameRate) [`kVTCompressionPropertyKey_BaseLayerFrameRateFraction`](/documentation/VideoToolbox/kVTCompressionPropertyKey_BaseLayerFrameRateFraction) ### Video Extended Usage (VEXU) Signaling [`kVTCompressionPropertyKey_HasLeftStereoEyeView`](/documentation/VideoToolbox/kVTCompressionPropertyKey_HasLeftStereoEyeView) [`kVTCompressionPropertyKey_HasRightStereoEyeView`](/documentation/VideoToolbox/kVTCompressionPropertyKey_HasRightStereoEyeView) [`kVTCompressionPropertyKey_HeroEye`](/documentation/VideoToolbox/kVTCompressionPropertyKey_HeroEye) A value that indicates which eye is the primary eye when rendering in 2D. [`kVTCompressionPropertyKey_HorizontalDisparityAdjustment`](/documentation/VideoToolbox/kVTCompressionPropertyKey_HorizontalDisparityAdjustment) A value that indicates a relative shift of the left and right images, which changes the zero parallax plane. [`kVTCompressionPropertyKey_HorizontalFieldOfView`](/documentation/VideoToolbox/kVTCompressionPropertyKey_HorizontalFieldOfView) [`kVTCompressionPropertyKey_ProjectionKind`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ProjectionKind) A value that indicates the projection kind. [`kVTCompressionPropertyKey_StereoCameraBaseline`](/documentation/VideoToolbox/kVTCompressionPropertyKey_StereoCameraBaseline) A value that specifies the distance between centers of the lenses of the camera system. [`kVTCompressionPropertyKey_ViewPackingKind`](/documentation/VideoToolbox/kVTCompressionPropertyKey_ViewPackingKind) A value that indicates the view packing kind. --- Copyright © 2026 Apple Inc. 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