registry/vulkan/chapters/video_decode_extensions.txt - third_party/platform/external/gfxstream-protocols - Git at Google

 // Copyright 2018-2021 The Khronos Group Inc.
 //
 // SPDX-License-Identifier: CC-BY-4.0

 [[video-decode-operations]]
 == Video Decode Operations

 Before the application can start recording Vulkan command buffers for the
 Video Decode Operations, it must: do the following, beforehand:

   . Ensure that the implementation can decode the Video Content by querying
     the supported codec operations and profiles using
     flink:vkGetPhysicalDeviceQueueFamilyProperties2.
   . By using flink:vkGetPhysicalDeviceVideoFormatPropertiesKHR and providing
     one or more video profiles, choose the Vulkan formats supported by the
     implementation.
     The formats for <<decoded-output-picture,output>> and
     <<reference-picture,reference>> pictures must: be queried and chosen
     separately.
     Refer to the section on
     <<supported-video-input-output-dpb-formats-enumeration,enumeration of
     supported video formats>>.
   . Before creating an image to be used as a video picture resource, obtain
     the supported image creation parameters by querying with
     flink:vkGetPhysicalDeviceFormatProperties2 and
     flink:vkGetPhysicalDeviceImageFormatProperties2 using one of the
     reported formats and adding slink:VkVideoProfilesKHR to the pname:pNext
     chain of slink:VkFormatProperties2.
     When querying the parameters with
     flink:vkGetPhysicalDeviceImageFormatProperties2 for images targeting
     decoded <<decoded-output-picture,output>> and
     <<reference-picture,reference (DPB)>> pictures, the
     slink:VkPhysicalDeviceImageFormatInfo2::pname:usage field should contain
     ename:VK_IMAGE_USAGE_VIDEO_DECODE_DST_BIT_KHR and
     ename:VK_IMAGE_USAGE_VIDEO_DECODE_DPB_BIT_KHR, respectively.
   . Create none, some, or all of the required <<VkImage,images>> for the
     <<decoded-output-picture,decoded output>> and
     <<reference-picture,reference>> pictures.
     More Video Picture Resources can: be created at some later point if
     needed while processing the decoded content.
     Also, if the decoded picture size is expected to change, the images can:
     be created based on the maximum decoded content size required.
   . Create the <<video-session,video session>> to be used for video decode
     operations.
     Before creating the Decode Video Session, the decode capabilities
     should: be queried with flink:vkGetPhysicalDeviceVideoCapabilitiesKHR to
     obtain the limits of the parameters allowed by the implementation for a
     particular codec profile.
   . Bind memory resources with the decode video session by calling
     flink:vkBindVideoSessionMemoryKHR.
     The video session cannot: be used until memory resources are allocated
     and bound to it.
     In order to determine the required memory sizes and heap types of the
     device memory allocations, flink:vkGetVideoSessionMemoryRequirementsKHR
     should: be called.
   . Create one or more <<video-session-parameters-introduction,Session
     Parameter objects>> for use across command buffer recording operations,
     if required by the codec extension in use.
     These objects must: be created against a <<video-session,video session>>
     with the parameters required by the codec.
     Each <<video-session-parameters-introduction,Session Parameter object>>
     created is a child object of the associated <<video-session, Session
     object>> and cannot: be bound in the command buffer with any other
     <<video-session,Session Object>>.

 The recording of Video Decode Commands against a Vulkan command buffer
 consists of the following sequence:

   . flink:vkCmdBeginVideoCodingKHR starts the recording of one or more Video
     Decode operations in the command buffer.
     For each Video Decode Command operation, a Video Session must: be bound
     to the command buffer within this command.
     This command establishes a Vulkan Video Decode Context that consists of
     the bound Video Session Object, Session Parameters Object, and the
     required Video Picture Resources.
     The established Video Decode Context is in effect until the
     flink:vkCmdEndVideoCodingKHR command is recorded.
     If more Video Decode operations are to be required after the
     flink:vkCmdEndVideoCodingKHR command, another Video Decode Context can:
     be started with the flink:vkCmdBeginVideoCodingKHR command.
   . flink:vkCmdDecodeVideoKHR specifies one or more compressed data buffers
     to be decoded.
     The slink:VkVideoDecodeInfoKHR parameters, and the codec extension
     structures chained to this, specify the details of the decode operation.
   . flink:vkCmdControlVideoCodingKHR records operations against the decoded
     data, decoding device, or the Video Session state.
   . flink:vkCmdEndVideoCodingKHR signals the end of the recording of the
     Vulkan Video Decode Context, as established by
     flink:vkCmdBeginVideoCodingKHR.

 In addition to the above, the following commands can: be recorded between
 flink:vkCmdBeginVideoCodingKHR and flink:vkCmdEndVideoCodingKHR:

   * Query operations
   * Global Memory Barriers
   * Buffer Memory Barriers
   * Image Memory Barriers (these must: be used to transition the Video
     Picture Resources to the proper
     ename:VK_IMAGE_LAYOUT_VIDEO_DECODE_DPB_KHR and
     ename:VK_IMAGE_LAYOUT_VIDEO_DECODE_DST_KHR layouts).
   * Pipeline Barriers
   * Events
   * Timestamps
   * Device Groups (device mask)

 The following Video Decode related commands must: be recorded *outside* the
 Vulkan Video Decode Context established with the
 flink:vkCmdBeginVideoCodingKHR and flink:vkCmdEndVideoCodingKHR commands:

   * Sparse Memory Binding
   * Copy Commands
   * Clear Commands


 [[video-picture-decode-modes]]
 === Video Picture Decode Modes

 There are a few ways that the flink:vkCmdDecodeVideoKHR can be configured
 for the Video Picture Decode Operations, based on:

   * if the <<decoded-output-picture, output resource>> would need to be used
     as <<reference-picture,Reference Picture>> for subsequent decode
     operations and;
   * if <<dpb-slot,DPB Slots>> are required for use as
     <<reference-picture,Reference Pictures>> indexes.

 [[video-picture-decode-no-reference-picture-no-slot-update]]
 The most basic Video Picture Decode operation with the
 flink:vkCmdDecodeVideoKHR command is to output the decoded pixel data
 without using any DPB <<reference-picture,Reference Pictures>> and without
 updating any <<dpb-slot,DPB Slot's>> indexes.

 In this case, the following slink:VkVideoDecodeInfoKHR parameters must: be
 set:

   * slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding
     must: be a valid slink:VkImageView.
     This slink:VkImageView represents the <<decoded-output-picture, output
     resource>> where the decoded pixels will be populated after a successful
     decode operation.
   * slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->slotIndex must:
     be an invalid <<dpb-slot,DPB Slot>> index (-1) since the decoded picture
     is not intended to be used as a reference picture with subsequent video
     decode operations.
   * The value of the slink:VkVideoDecodeInfoKHR::pname:referenceSlotCount
     can: be `0` and slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots can:
     be `NULL`.
   * If slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots is not `NULL`, it
     can: still have entries representing <<dpb-slot,DPB Slot>> indexes with
     a <<video-session-dpb-slot-states, Valid Picture Reference>>.
     The codec extension selects the actual use of the
     <<reference-picture,Reference Pictures>> by referring to a
     <<dpb-slot,DPB Slot>> index with a <<video-session-dpb-slot-states,
     Valid Picture Reference>>.

 [[video-picture-decode-with-references-no-slot-update]]

 Video Picture Decode operations with the flink:vkCmdDecodeVideoKHR command,
 requiring one or more <<reference-picture,Reference Pictures>> for the
 predictions of the values of samples for the <<decoded-output-picture,
 decoded output picture>> would require <<dpb-slot,DPB Slots>> with
 <<video-session-dpb-slot-states, Valid Picture Reference>>.

 In this case, the following slink:VkVideoDecodeInfoKHR parameters must: be
 set:

   * slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding
     must: be a valid slink:VkImageView.
     This slink:VkImageView represents the <<decoded-output-picture, output
     resource>> where the decoded pixels will be populated after a successful
     decode operation.
   * slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->slotIndex must:
     be an invalid <<dpb-slot,DPB Slot>> index (-1) since the decoded picture
     is not intended to be used as a reference picture with subsequent video
     decode operations.
   * The value of the slink:VkVideoDecodeInfoKHR::pname:referenceSlotCount
     must: not be `0` and slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots
     should represent at least the number of the reference slots required for
     the decode operation.
     The codec extension selects the actual use of the
     <<reference-picture,Reference Pictures>> by referring to a
     <<dpb-slot,DPB Slot>> index with a <<video-session-dpb-slot-states,
     Valid Picture Reference>>.
     If the implementation does not use an opaque DPB, each <<dpb-slot,DPB
     slot>> representing a <<reference-picture,reference picture>> must:
     refer to a valid <<VkImageView,image view>>.
     The <<VkImageView,image views>> must: represent the same
     <<resources-images, image resources>> that were used to create the
     <<reference-picture,reference picture>> for the corresponding
     <<dpb-slot,DPB Slot>> index.
   * slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots can: still have
     entries representing <<dpb-slot,DPB Slot>> indexes with a
     <<video-session-dpb-slot-states, Valid Picture Reference>>.

 After the flink:vkCmdDecodeVideoKHR operation is completed successfully, the
 slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding
 pixel data will be updated with the decoded content.
 The operation will not update any <<dpb-slot,DPB Slot>> with
 <<reference-picture,Reference Pictures>> data.
 However, any <<dpb-slot,DPB Slot>> activation, invalidation, or deactivation
 operations requested via slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots
 are still going to be performed.

 image::images/DecodeSessionDpbDecodeWithOutputToVkImageViewNoReferencePictureSlotUpdate.svg[align="center",title="Decoding a Frame to VkImageView without a slot update for a *Reference Picture*",opts="{imageopts}"]


 [[video-picture-decode-with-reference-picture-and-slot-update]]
 ==== Video Picture Decode with a <<reference-picture,Reference Picture>> slot update and using optional <<reference-picture,Reference Pictures>>

 When it is known that the picture to be decoded will be used as a
 <<reference-picture,reference picture>> for subsequent decode operations,
 one of the available <<dpb-slot,DPB Slots>> needs to be selected for
 <<video-session-activating-dpb-slot, activation and update>> operations as
 part of the flink:vkCmdDecodeVideoKHR command.

 Based on whether a decode operation
 <<video-picture-decode-with-references-no-slot-update, with reference
 pictures>> or <<video-picture-decode-no-reference-picture-no-slot-update,
 without reference pictures>> is required, the flink:vkCmdDecodeVideoKHR
 should be configured with parameters as described in the previous sections.
 In addition, one of the available <<dpb-slot,DPB Slots>> must: be selected
 by the application, activated with resources and then set-up for an update
 with the decode operation.

 In this case, the following slink:VkVideoDecodeInfoKHR parameters must: be
 set:

   * slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding
     must: be a valid slink:VkImageView.
     This slink:VkImageView represents the <<decoded-output-picture, output
     resource>> where the decoded pixels will be populated after a successful
     decode operation.
     If the implementation does not use an opaque DPB, both the
     <<decoded-output-picture, output>> and <<reference-picture,reference
     picture>> resource coincide.
   * slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->slotIndex must:
     be a valid <<dpb-slot,DPB Slot>> index selected by the application,
     based on the currently available slots.
   * slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots can: still have
     entries representing <<dpb-slot,DPB Slot>> indexes with a
     <<video-session-dpb-slot-states, Valid Picture Reference>>.

 After the flink:vkCmdDecodeVideoKHR operation has completed successfully,
 the decoded content will be available in the resource provided for
 slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding.
 In addition, this operation will update the selected <<dpb-slot,DPB Slot>>
 with <<reference-picture,Reference Pictures>> data.
 Any other <<dpb-slot,DPB Slot>> activation,invalidation, or deactivation
 operation requested via the
 slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots are going to be performed
 as well.

 image::images/DecodeSessionDpbDecodeWithOutputToReferencePictureSlot.svg[align="center",title="Decoding a Frame to VkImageView with an update to a <<reference-picture,Reference Pictures>> DPB Slot",opts="{imageopts}"]


 === Video Decode Command Buffer Commands

 [open,refpage='vkCmdDecodeVideoKHR',desc='Decode a frame',type='protos']
 --
 To decode a frame, call:

 include::{generated}/api/protos/vkCmdDecodeVideoKHR.txt[]

   * pname:commandBuffer is the command buffer to be filled with this
     function for decode frame command.
   * pname:pFrameInfo is a pointer to a slink:VkVideoDecodeInfoKHR structure.

 include::{generated}/validity/protos/vkCmdDecodeVideoKHR.txt[]
 --

 [open,refpage='VkVideoDecodeInfoKHR',desc='Structure specifying parameters of decoding a frame',type='structs']
 --
 The slink:VkVideoDecodeInfoKHR structure is defined as:

 include::{generated}/api/structs/VkVideoDecodeInfoKHR.txt[]
   * pname:sType is the type of this structure.
   * pname:pNext is `NULL` or a pointer to a structure extending this
     structure.
     All the codec specific structures related to each frame(picture
     parameters, quantization matrix, etc.) must: be chained here and pass to
     decode session with the function call flink:vkCmdDecodeVideoKHR.
   * pname:flags is a bitmask of elink:VkVideoDecodeFlagBitsKHR specifying
     decode flags, reserved for future versions of this specification.
   * pname:codedOffset is the coded offset of the decode operations.
     The purpose of this field is interpreted based on the codec extension.
 ifdef::VK_EXT_video_decode_h264[]
     When decoding content in H.264 field mode, the pname:codedOffset
     specifies the line or picture field's offset within the image.
 endif::VK_EXT_video_decode_h264[]
   * pname:codedExtent is the coded size of the decode operations.
   * pname:srcBuffer is the source buffer that holds the encoded bitstream.
   * pname:srcBufferOffset is the buffer offset where the valid encoded
     bitstream starts in srcBuffer.
     It must: meet the alignment requirement
     pname:minBitstreamBufferOffsetAlignment within
     slink:VkVideoCapabilitiesKHR queried with the
     flink:vkGetPhysicalDeviceVideoCapabilitiesKHR function.
   * pname:srcBufferRange is the size of the srcBuffer with valid encoded
     bitstream, starting from pname:srcBufferOffset.
     It must: meet the alignment requirement
     pname:minBitstreamBufferSizeAlignment within
     slink:VkVideoCapabilitiesKHR queried with the
     flink:vkGetPhysicalDeviceVideoCapabilitiesKHR function.
   * pname:dstPictureResource is the destination
     <<decoded-output-picture,Decoded Output Picture>> Resource.
   * pname:pSetupReferenceSlot is `NULL` or a pointer to a
     slink:VkVideoReferenceSlotKHR structure used for generating a DPB
     reference slot and Picture Resource.
     pname:pSetupReferenceSlot->slotIndex specifies the slot index number to
     use as a target for producing the DPB data.
     pname:slotIndex must: reference a valid entry as specified in
     slink:VkVideoBeginCodingInfoKHR via the pname:pReferenceSlots within the
     flink:vkCmdBeginVideoCodingKHR command that established the Vulkan Video
     Decode Context for this command.
   * pname:referenceSlotCount is the number of the DPB Reference Pictures
     that will be used when this decoding operation is executing.
   * pname:pReferenceSlots is a pointer to an array of
     slink:VkVideoReferenceSlotKHR structures specifying the DPB Reference
     pictures that will be used when this decoding operation is executing.

 include::{generated}/validity/structs/VkVideoDecodeInfoKHR.txt[]
 --

 [open,refpage='VkVideoDecodeFlagBitsKHR',desc='Video Decode Command Flags',type='enums']
 --
 The flink:vkCmdDecodeVideoKHR flags are defined with the following
 enumeration:

 include::{generated}/api/enums/VkVideoDecodeFlagBitsKHR.txt[]

   * ename:VK_VIDEO_DECODE_RESERVED_0_BIT_KHR The current version of the
     specification has reserved this value for future use.
 --

 [open,refpage='VkVideoDecodeFlagsKHR',desc='Bitmask specifying the video decode flink:vkCmdDecodeVideoKHR flags',type='flags']
 --
 include::{generated}/api/flags/VkVideoDecodeFlagsKHR.txt[]

 tlink:VkVideoDecodeFlagsKHR is a bitmask type for setting a mask of zero or
 more elink:VkVideoDecodeFlagBitsKHR.
 --
	// Copyright 2018-2021 The Khronos Group Inc.
	//
	// SPDX-License-Identifier: CC-BY-4.0

	[[video-decode-operations]]
	== Video Decode Operations

	Before the application can start recording Vulkan command buffers for the
	Video Decode Operations, it must: do the following, beforehand:

	. Ensure that the implementation can decode the Video Content by querying
	the supported codec operations and profiles using
	flink:vkGetPhysicalDeviceQueueFamilyProperties2.
	. By using flink:vkGetPhysicalDeviceVideoFormatPropertiesKHR and providing
	one or more video profiles, choose the Vulkan formats supported by the
	implementation.
	The formats for <<decoded-output-picture,output>> and
	<<reference-picture,reference>> pictures must: be queried and chosen
	separately.
	Refer to the section on
	<<supported-video-input-output-dpb-formats-enumeration,enumeration of
	supported video formats>>.
	. Before creating an image to be used as a video picture resource, obtain
	the supported image creation parameters by querying with
	flink:vkGetPhysicalDeviceFormatProperties2 and
	flink:vkGetPhysicalDeviceImageFormatProperties2 using one of the
	reported formats and adding slink:VkVideoProfilesKHR to the pname:pNext
	chain of slink:VkFormatProperties2.
	When querying the parameters with
	flink:vkGetPhysicalDeviceImageFormatProperties2 for images targeting
	decoded <<decoded-output-picture,output>> and
	<<reference-picture,reference (DPB)>> pictures, the
	slink:VkPhysicalDeviceImageFormatInfo2::pname:usage field should contain
	ename:VK_IMAGE_USAGE_VIDEO_DECODE_DST_BIT_KHR and
	ename:VK_IMAGE_USAGE_VIDEO_DECODE_DPB_BIT_KHR, respectively.
	. Create none, some, or all of the required <<VkImage,images>> for the
	<<decoded-output-picture,decoded output>> and
	<<reference-picture,reference>> pictures.
	More Video Picture Resources can: be created at some later point if
	needed while processing the decoded content.
	Also, if the decoded picture size is expected to change, the images can:
	be created based on the maximum decoded content size required.
	. Create the <<video-session,video session>> to be used for video decode
	operations.
	Before creating the Decode Video Session, the decode capabilities
	should: be queried with flink:vkGetPhysicalDeviceVideoCapabilitiesKHR to
	obtain the limits of the parameters allowed by the implementation for a
	particular codec profile.
	. Bind memory resources with the decode video session by calling
	flink:vkBindVideoSessionMemoryKHR.
	The video session cannot: be used until memory resources are allocated
	and bound to it.
	In order to determine the required memory sizes and heap types of the
	device memory allocations, flink:vkGetVideoSessionMemoryRequirementsKHR
	should: be called.
	. Create one or more <<video-session-parameters-introduction,Session
	Parameter objects>> for use across command buffer recording operations,
	if required by the codec extension in use.
	These objects must: be created against a <<video-session,video session>>
	with the parameters required by the codec.
	Each <<video-session-parameters-introduction,Session Parameter object>>
	created is a child object of the associated <<video-session, Session
	object>> and cannot: be bound in the command buffer with any other
	<<video-session,Session Object>>.

	The recording of Video Decode Commands against a Vulkan command buffer
	consists of the following sequence:

	. flink:vkCmdBeginVideoCodingKHR starts the recording of one or more Video
	Decode operations in the command buffer.
	For each Video Decode Command operation, a Video Session must: be bound
	to the command buffer within this command.
	This command establishes a Vulkan Video Decode Context that consists of
	the bound Video Session Object, Session Parameters Object, and the
	required Video Picture Resources.
	The established Video Decode Context is in effect until the
	flink:vkCmdEndVideoCodingKHR command is recorded.
	If more Video Decode operations are to be required after the
	flink:vkCmdEndVideoCodingKHR command, another Video Decode Context can:
	be started with the flink:vkCmdBeginVideoCodingKHR command.
	. flink:vkCmdDecodeVideoKHR specifies one or more compressed data buffers
	to be decoded.
	The slink:VkVideoDecodeInfoKHR parameters, and the codec extension
	structures chained to this, specify the details of the decode operation.
	. flink:vkCmdControlVideoCodingKHR records operations against the decoded
	data, decoding device, or the Video Session state.
	. flink:vkCmdEndVideoCodingKHR signals the end of the recording of the
	Vulkan Video Decode Context, as established by
	flink:vkCmdBeginVideoCodingKHR.

	In addition to the above, the following commands can: be recorded between
	flink:vkCmdBeginVideoCodingKHR and flink:vkCmdEndVideoCodingKHR:

	* Query operations
	* Global Memory Barriers
	* Buffer Memory Barriers
	* Image Memory Barriers (these must: be used to transition the Video
	Picture Resources to the proper
	ename:VK_IMAGE_LAYOUT_VIDEO_DECODE_DPB_KHR and
	ename:VK_IMAGE_LAYOUT_VIDEO_DECODE_DST_KHR layouts).
	* Pipeline Barriers
	* Events
	* Timestamps
	* Device Groups (device mask)

	The following Video Decode related commands must: be recorded outside the
	Vulkan Video Decode Context established with the
	flink:vkCmdBeginVideoCodingKHR and flink:vkCmdEndVideoCodingKHR commands:

	* Sparse Memory Binding
	* Copy Commands
	* Clear Commands


	[[video-picture-decode-modes]]
	=== Video Picture Decode Modes

	There are a few ways that the flink:vkCmdDecodeVideoKHR can be configured
	for the Video Picture Decode Operations, based on:

	* if the <<decoded-output-picture, output resource>> would need to be used
	as <<reference-picture,Reference Picture>> for subsequent decode
	operations and;
	* if <<dpb-slot,DPB Slots>> are required for use as
	<<reference-picture,Reference Pictures>> indexes.

	[[video-picture-decode-no-reference-picture-no-slot-update]]
	The most basic Video Picture Decode operation with the
	flink:vkCmdDecodeVideoKHR command is to output the decoded pixel data
	without using any DPB <<reference-picture,Reference Pictures>> and without
	updating any <<dpb-slot,DPB Slot's>> indexes.

	In this case, the following slink:VkVideoDecodeInfoKHR parameters must: be
	set:

	* slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding
	must: be a valid slink:VkImageView.
	This slink:VkImageView represents the <<decoded-output-picture, output
	resource>> where the decoded pixels will be populated after a successful
	decode operation.
	* slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->slotIndex must:
	be an invalid <<dpb-slot,DPB Slot>> index (-1) since the decoded picture
	is not intended to be used as a reference picture with subsequent video
	decode operations.
	* The value of the slink:VkVideoDecodeInfoKHR::pname:referenceSlotCount
	can: be `0` and slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots can:
	be `NULL`.
	* If slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots is not `NULL`, it
	can: still have entries representing <<dpb-slot,DPB Slot>> indexes with
	a <<video-session-dpb-slot-states, Valid Picture Reference>>.
	The codec extension selects the actual use of the
	<<reference-picture,Reference Pictures>> by referring to a
	<<dpb-slot,DPB Slot>> index with a <<video-session-dpb-slot-states,
	Valid Picture Reference>>.

	[[video-picture-decode-with-references-no-slot-update]]

	Video Picture Decode operations with the flink:vkCmdDecodeVideoKHR command,
	requiring one or more <<reference-picture,Reference Pictures>> for the
	predictions of the values of samples for the <<decoded-output-picture,
	decoded output picture>> would require <<dpb-slot,DPB Slots>> with
	<<video-session-dpb-slot-states, Valid Picture Reference>>.

	In this case, the following slink:VkVideoDecodeInfoKHR parameters must: be
	set:

	* slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding
	must: be a valid slink:VkImageView.
	This slink:VkImageView represents the <<decoded-output-picture, output
	resource>> where the decoded pixels will be populated after a successful
	decode operation.
	* slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->slotIndex must:
	be an invalid <<dpb-slot,DPB Slot>> index (-1) since the decoded picture
	is not intended to be used as a reference picture with subsequent video
	decode operations.
	* The value of the slink:VkVideoDecodeInfoKHR::pname:referenceSlotCount
	must: not be `0` and slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots
	should represent at least the number of the reference slots required for
	the decode operation.
	The codec extension selects the actual use of the
	<<reference-picture,Reference Pictures>> by referring to a
	<<dpb-slot,DPB Slot>> index with a <<video-session-dpb-slot-states,
	Valid Picture Reference>>.
	If the implementation does not use an opaque DPB, each <<dpb-slot,DPB
	slot>> representing a <<reference-picture,reference picture>> must:
	refer to a valid <<VkImageView,image view>>.
	The <<VkImageView,image views>> must: represent the same
	<<resources-images, image resources>> that were used to create the
	<<reference-picture,reference picture>> for the corresponding
	<<dpb-slot,DPB Slot>> index.
	* slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots can: still have
	entries representing <<dpb-slot,DPB Slot>> indexes with a
	<<video-session-dpb-slot-states, Valid Picture Reference>>.

	After the flink:vkCmdDecodeVideoKHR operation is completed successfully, the
	slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding
	pixel data will be updated with the decoded content.
	The operation will not update any <<dpb-slot,DPB Slot>> with
	<<reference-picture,Reference Pictures>> data.
	However, any <<dpb-slot,DPB Slot>> activation, invalidation, or deactivation
	operations requested via slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots
	are still going to be performed.

	image::images/DecodeSessionDpbDecodeWithOutputToVkImageViewNoReferencePictureSlotUpdate.svg[align="center",title="Decoding a Frame to VkImageView without a slot update for a Reference Picture",opts="{imageopts}"]


	[[video-picture-decode-with-reference-picture-and-slot-update]]
	==== Video Picture Decode with a <<reference-picture,Reference Picture>> slot update and using optional <<reference-picture,Reference Pictures>>

	When it is known that the picture to be decoded will be used as a
	<<reference-picture,reference picture>> for subsequent decode operations,
	one of the available <<dpb-slot,DPB Slots>> needs to be selected for
	<<video-session-activating-dpb-slot, activation and update>> operations as
	part of the flink:vkCmdDecodeVideoKHR command.

	Based on whether a decode operation
	<<video-picture-decode-with-references-no-slot-update, with reference
	pictures>> or <<video-picture-decode-no-reference-picture-no-slot-update,
	without reference pictures>> is required, the flink:vkCmdDecodeVideoKHR
	should be configured with parameters as described in the previous sections.
	In addition, one of the available <<dpb-slot,DPB Slots>> must: be selected
	by the application, activated with resources and then set-up for an update
	with the decode operation.

	In this case, the following slink:VkVideoDecodeInfoKHR parameters must: be
	set:

	* slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding
	must: be a valid slink:VkImageView.
	This slink:VkImageView represents the <<decoded-output-picture, output
	resource>> where the decoded pixels will be populated after a successful
	decode operation.
	If the implementation does not use an opaque DPB, both the
	<<decoded-output-picture, output>> and <<reference-picture,reference
	picture>> resource coincide.
	* slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->slotIndex must:
	be a valid <<dpb-slot,DPB Slot>> index selected by the application,
	based on the currently available slots.
	* slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots can: still have
	entries representing <<dpb-slot,DPB Slot>> indexes with a
	<<video-session-dpb-slot-states, Valid Picture Reference>>.

	After the flink:vkCmdDecodeVideoKHR operation has completed successfully,
	the decoded content will be available in the resource provided for
	slink:VkVideoDecodeInfoKHR::pname:pSetupReferenceSlot->pPictureResource->imageViewBinding.
	In addition, this operation will update the selected <<dpb-slot,DPB Slot>>
	with <<reference-picture,Reference Pictures>> data.
	Any other <<dpb-slot,DPB Slot>> activation,invalidation, or deactivation
	operation requested via the
	slink:VkVideoDecodeInfoKHR::pname:pReferenceSlots are going to be performed
	as well.

	image::images/DecodeSessionDpbDecodeWithOutputToReferencePictureSlot.svg[align="center",title="Decoding a Frame to VkImageView with an update to a <<reference-picture,Reference Pictures>> DPB Slot",opts="{imageopts}"]


	=== Video Decode Command Buffer Commands

	[open,refpage='vkCmdDecodeVideoKHR',desc='Decode a frame',type='protos']
	--
	To decode a frame, call:

	include::{generated}/api/protos/vkCmdDecodeVideoKHR.txt[]

	* pname:commandBuffer is the command buffer to be filled with this
	function for decode frame command.
	* pname:pFrameInfo is a pointer to a slink:VkVideoDecodeInfoKHR structure.

	include::{generated}/validity/protos/vkCmdDecodeVideoKHR.txt[]
	--

	[open,refpage='VkVideoDecodeInfoKHR',desc='Structure specifying parameters of decoding a frame',type='structs']
	--
	The slink:VkVideoDecodeInfoKHR structure is defined as:

	include::{generated}/api/structs/VkVideoDecodeInfoKHR.txt[]
	* pname:sType is the type of this structure.
	* pname:pNext is `NULL` or a pointer to a structure extending this
	structure.
	All the codec specific structures related to each frame(picture
	parameters, quantization matrix, etc.) must: be chained here and pass to
	decode session with the function call flink:vkCmdDecodeVideoKHR.
	* pname:flags is a bitmask of elink:VkVideoDecodeFlagBitsKHR specifying
	decode flags, reserved for future versions of this specification.
	* pname:codedOffset is the coded offset of the decode operations.
	The purpose of this field is interpreted based on the codec extension.
	ifdef::VK_EXT_video_decode_h264[]
	When decoding content in H.264 field mode, the pname:codedOffset
	specifies the line or picture field's offset within the image.
	endif::VK_EXT_video_decode_h264[]
	* pname:codedExtent is the coded size of the decode operations.
	* pname:srcBuffer is the source buffer that holds the encoded bitstream.
	* pname:srcBufferOffset is the buffer offset where the valid encoded
	bitstream starts in srcBuffer.
	It must: meet the alignment requirement
	pname:minBitstreamBufferOffsetAlignment within
	slink:VkVideoCapabilitiesKHR queried with the
	flink:vkGetPhysicalDeviceVideoCapabilitiesKHR function.
	* pname:srcBufferRange is the size of the srcBuffer with valid encoded
	bitstream, starting from pname:srcBufferOffset.
	It must: meet the alignment requirement
	pname:minBitstreamBufferSizeAlignment within
	slink:VkVideoCapabilitiesKHR queried with the
	flink:vkGetPhysicalDeviceVideoCapabilitiesKHR function.
	* pname:dstPictureResource is the destination
	<<decoded-output-picture,Decoded Output Picture>> Resource.
	* pname:pSetupReferenceSlot is `NULL` or a pointer to a
	slink:VkVideoReferenceSlotKHR structure used for generating a DPB
	reference slot and Picture Resource.
	pname:pSetupReferenceSlot->slotIndex specifies the slot index number to
	use as a target for producing the DPB data.
	pname:slotIndex must: reference a valid entry as specified in
	slink:VkVideoBeginCodingInfoKHR via the pname:pReferenceSlots within the
	flink:vkCmdBeginVideoCodingKHR command that established the Vulkan Video
	Decode Context for this command.
	* pname:referenceSlotCount is the number of the DPB Reference Pictures
	that will be used when this decoding operation is executing.
	* pname:pReferenceSlots is a pointer to an array of
	slink:VkVideoReferenceSlotKHR structures specifying the DPB Reference
	pictures that will be used when this decoding operation is executing.

	include::{generated}/validity/structs/VkVideoDecodeInfoKHR.txt[]
	--

	[open,refpage='VkVideoDecodeFlagBitsKHR',desc='Video Decode Command Flags',type='enums']
	--
	The flink:vkCmdDecodeVideoKHR flags are defined with the following
	enumeration:

	include::{generated}/api/enums/VkVideoDecodeFlagBitsKHR.txt[]

	* ename:VK_VIDEO_DECODE_RESERVED_0_BIT_KHR The current version of the
	specification has reserved this value for future use.
	--

	[open,refpage='VkVideoDecodeFlagsKHR',desc='Bitmask specifying the video decode flink:vkCmdDecodeVideoKHR flags',type='flags']
	--
	include::{generated}/api/flags/VkVideoDecodeFlagsKHR.txt[]

	tlink:VkVideoDecodeFlagsKHR is a bitmask type for setting a mask of zero or
	more elink:VkVideoDecodeFlagBitsKHR.
	--