C Specification

The VkVideoDecodeH264DpbSlotInfoKHR structure is defined as:

// Provided by VK_KHR_video_decode_h264
typedef struct VkVideoDecodeH264DpbSlotInfoKHR {
    VkStructureType                           sType;
    const void*                               pNext;
    const StdVideoDecodeH264ReferenceInfo*    pStdReferenceInfo;
} VkVideoDecodeH264DpbSlotInfoKHR;

Members

  • sType is a VkStructureType value identifying this structure.

  • pNext is NULL or a pointer to a structure extending this structure.

  • pStdReferenceInfo is a pointer to a StdVideoDecodeH264ReferenceInfo structure specifying H.264 reference information.

Description

This structure is specified in the pNext chain of VkVideoDecodeInfoKHR::pSetupReferenceSlot, if not NULL, and the pNext chain of the elements of VkVideoDecodeInfoKHR::pReferenceSlots to specify the codec-specific reference picture information for an H.264 decode operation.

Active Reference Picture Information

When this structure is specified in the pNext chain of the elements of VkVideoDecodeInfoKHR::pReferenceSlots, one or two elements are added to the list of active reference pictures used by the video decode operation for each element of VkVideoDecodeInfoKHR::pReferenceSlots as follows:

  • If neither pStdReferenceInfo->flags.top_field_flag nor pStdReferenceInfo->flags.bottom_field_flag is set, then the picture is added as a frame reference to the list of active reference pictures.

  • If pStdReferenceInfo->flags.top_field_flag is set, then the picture is added as a top field reference to the list of active reference pictures.

  • If pStdReferenceInfo->flags.bottom_field_flag is set, then the picture is added as a bottom field reference to the list of active reference pictures.

  • For each added reference picture, the corresponding image subregion used is determined according to the H.264 Decode Picture Data Access section.

  • Each added reference picture is associated with the DPB slot index specified in the slotIndex member of the corresponding element of VkVideoDecodeInfoKHR::pReferenceSlots.

  • Each added reference picture is associated with the H.264 reference information provided in pStdReferenceInfo.

Note

When both the top and bottom field of an interlaced frame currently associated with a DPB slot is intended to be used as an active reference picture and both fields are stored in the same image subregion (which is the case when using VK_VIDEO_DECODE_H264_PICTURE_LAYOUT_INTERLACED_INTERLEAVED_LINES_BIT_KHR which stores the two fields at even and odd scanlines of the same image subregion), both references have to be provided through a single VkVideoReferenceSlotInfoKHR structure that has both flags.top_field_flag and flags.bottom_field_flag set in the StdVideoDecodeH264ReferenceInfo structure pointed to by the pStdReferenceInfo member of the VkVideoDecodeH264DpbSlotInfoKHR structure included in the corresponding VkVideoReferenceSlotInfoKHR structure’s pNext chain. However, this approach can only be used when both fields are stored in the same image subregion. If that is not the case (e.g. when using VK_VIDEO_DECODE_H264_PICTURE_LAYOUT_INTERLACED_SEPARATE_PLANES_BIT_KHR which requires separate codedOffset values for the two fields and also allows storing the two fields of a frame in separate image layers or entirely separate images), then a separate VkVideoReferenceSlotInfoKHR structure needs to be provided for referencing the two fields, each only setting one of flags.top_field_flag or flags.bottom_field_flag, and providing the appropriate video picture resource information in VkVideoReferenceSlotInfoKHR::pPictureResource.
Reconstructed Picture Information

When this structure is specified in the pNext chain of VkVideoDecodeInfoKHR::pSetupReferenceSlot, the information related to the reconstructed picture is defined as follows:

  • If neither pStdReferenceInfo->flags.top_field_flag nor pStdReferenceInfo->flags.bottom_field_flag is set, then the picture represents a frame.

  • If pStdReferenceInfo->flags.top_field_flag is set, then the picture represents a field, specifically, the top field of the frame.

  • If pStdReferenceInfo->flags.bottom_field_flag is set, then the picture represents a field, specifically, the bottom field of the frame.

  • The image subregion used is determined according to the H.264 Decode Picture Data Access section.

  • The reconstructed picture is used to activate the DPB slot with the index specified in VkVideoDecodeInfoKHR::pSetupReferenceSlot->slotIndex.

  • The reconstructed picture is associated with the H.264 reference information provided in pStdReferenceInfo.

Std Reference Information

The members of the StdVideoDecodeH264ReferenceInfo structure pointed to by pStdReferenceInfo are interpreted as follows:

  • flags.top_field_flag is used to indicate whether the reference is used as top field reference;

  • flags.bottom_field_flag is used to indicate whether the reference is used as bottom field reference;

  • flags.used_for_long_term_reference is used to indicate whether the picture is marked as “used for long-term reference” as defined in section 8.2.5.1 of the ITU-T H.264 Specification;

  • flags.is_non_existing is used to indicate whether the picture is marked as “non-existing” as defined in section 8.2.5.2 of the ITU-T H.264 Specification;

  • all other members are interpreted as defined in section 8.2 of the ITU-T H.264 Specification.

Valid Usage (Implicit)

  • VUID-VkVideoDecodeH264DpbSlotInfoKHR-sType-sType
    sType must be VK_STRUCTURE_TYPE_VIDEO_DECODE_H264_DPB_SLOT_INFO_KHR

  • VUID-VkVideoDecodeH264DpbSlotInfoKHR-pStdReferenceInfo-parameter
    pStdReferenceInfo must be a valid pointer to a valid StdVideoDecodeH264ReferenceInfo value

See Also

VK_KHR_video_decode_h264, VkStructureType

Document Notes

For more information, see the Vulkan Specification

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.

Copyright

Copyright 2014-2023 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0