xref: /third_party/vk-gl-cts/external/vulkan-docs/src/chapters/video/h264_encode.adoc

// Copyright 2018-2024 The Khronos Group Inc.
//
// SPDX-License-Identifier: CC-BY-4.0

[[encode-h264]]
== H.264 Encode Operations

Video encode operations using an <<encode-h264-profile,H.264 encode
profile>> can: be used to encode elementary video stream sequences compliant
to the <<itu-t-h264,ITU-T H.264 Specification>>.

[NOTE]
.Note
====
Refer to the <<preamble, Preamble>> for information on how the Khronos
Intellectual Property Rights Policy relates to normative references to
external materials not created by Khronos.
====

This process is performed according to the <<encode-operation-steps,video
encode operation steps>> with the codec-specific semantics defined in
section 8 of the <<itu-t-h264,ITU-T H.264 Specification>> as follows:

  * Syntax elements, derived values, and other parameters are applied from
    the following structures:
  ** The code:StdVideoH264SequenceParameterSet structure corresponding to
     the <<encode-h264-active-sps,active SPS>> specifying the
     <<encode-h264-sps, H.264 sequence parameter set>>.
  ** The code:StdVideoH264PictureParameterSet structure corresponding to the
     <<encode-h264-active-pps,active PPS>> specifying the <<encode-h264-pps,
     H.264 picture parameter set>>.
  ** The code:StdVideoEncodeH264PictureInfo structure specifying the
     <<encode-h264-picture-info,H.264 picture information>>.
  ** The code:StdVideoEncodeH264SliceHeader structures specifying the
     <<encode-h264-slice-header-params,H.264 slice header parameters>> for
     each encoded H.264 slice.
  ** The code:StdVideoEncodeH264ReferenceInfo structures specifying the
     <<encode-h264-reference-info,H.264 reference information>>
     corresponding to the optional <<reconstructed-picture,reconstructed
     picture>> and any <<active-reference-pictures,active reference
     pictures>>.
  * The encoded bitstream data is written to the destination video bitstream
     buffer range as defined in the
     <<encode-h264-bitstream-data-access,H.264 Encode Bitstream Data
     Access>> section.
  * Picture data in the <<video-picture-resources,video picture resources>>
     corresponding to the used <<encode-input-picture,encode input
     picture>>, <<active-reference-pictures,active reference pictures>>, and
     optional <<reconstructed-picture,reconstructed picture>> is accessed as
     defined in the <<encode-h264-picture-data-access,H.264 Encode Picture
     Data Access>> section.
  * The decision on <<encode-ref-pic-setup,reference picture setup>> is made
    according to the parameters specified in the
    <<encode-h264-ref-pic-setup,H.264 picture information>>.

If the parameters adhere to the syntactic and semantic requirements defined
in the corresponding sections of the <<itu-t-h264,ITU-T H.264
Specification>>, as described above, and the <<dpb-slot,DPB slots>>
associated with the <<active-reference-pictures,active reference pictures>>
all refer to <<dpb-slot-states,valid picture references>>, then the video
encode operation will complete successfully.
Otherwise, the video encode operation may: complete
<<encode-unsuccessful,unsuccessfully>>.


[[encode-h264-overrides]]
=== H.264 Encode Parameter Overrides

Implementations may: override, unless otherwise specified, any of the H.264
encode parameters specified in the following Video Std structures:

  * code:StdVideoH264SequenceParameterSet
  * code:StdVideoH264PictureParameterSet
  * code:StdVideoEncodeH264PictureInfo
  * code:StdVideoEncodeH264SliceHeader
  * code:StdVideoEncodeH264ReferenceInfo

All such H.264 encode parameter overrides must: fulfill the conditions
defined in the <<encode-overrides,Video Encode Parameter Overrides>>
section.

In addition, implementations must: not override any of the following H.264
encode parameters:

  * code:StdVideoEncodeH264PictureInfo::code:primary_pic_type
  * code:StdVideoEncodeH264SliceHeader::code:slice_type

In case of H.264 encode parameters stored in
<<encode-h264-parameter-sets,video session parameters>> objects,
applications need to use the flink:vkGetEncodedVideoSessionParametersKHR
command to determine whether any implementation overrides happened.
If the query indicates that implementation overrides were applied, then the
application needs to retrieve and use the encoded H.264 parameter sets in
the bitstream in order to be able to produce a compliant H.264 video
bitstream using the H.264 encode parameters stored in the video session
parameters object.

In case of any H.264 encode parameters stored in the encoded bitstream
produced by video encode operations, if the implementation supports the
ename:VK_VIDEO_ENCODE_FEEDBACK_BITSTREAM_HAS_OVERRIDES_BIT_KHR
<<queries-video-encode-feedback,video encode feedback query>> flag, the
application can: use such queries to retrieve feedback about whether any
implementation overrides have been applied to those H.264 encode parameters.


[[encode-h264-bitstream-data-access]]
=== H.264 Encode Bitstream Data Access

Each video encode operation writes one or more VCL NAL units comprising of
slice headers and data of the encoded picture, in the format defined in
sections 7.3.3 and 7.3.4, according to the semantics defined in sections
7.4.3 and 7.4.4 of the <<itu-t-h264,ITU-T H.264 Specification>>,
respectively.
The number of VCL NAL units written is specified by
slink:VkVideoEncodeH264PictureInfoKHR::pname:naluSliceEntryCount.

In addition, if
slink:VkVideoEncodeH264PictureInfoKHR::pname:generatePrefixNalu is set to
ename:VK_TRUE for the video encode operation, then an additional prefix NAL
unit is written before each VCL NAL unit corresponding to individual slices
in the format defined in section 7.3.2.12, according to the semantics
defined in section 7.4.2.12 of the <<itu-t-h264,ITU-T H.264 Specification>>,
respectively.


[[encode-h264-picture-data-access]]
=== H.264 Encode Picture Data Access

Accesses to image data within a video picture resource happen at the
granularity indicated by
slink:VkVideoCapabilitiesKHR::pname:pictureAccessGranularity, as returned by
flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used <<video-profiles,
video profile>>.
Accordingly, the complete image subregion of a <<encode-input-picture,encode
input picture>>, <<reference-picture,reference picture>>, or
<<reconstructed-picture,reconstructed picture>> accessed by video coding
operations using an <<encode-h264-profile,H.264 encode profile>> is defined
as the set of texels within the coordinate range:

  {empty}:: [eq]#([0,pname:endX),[0,pname:endY))#

Where:

  * [eq]#pname:endX# equals [eq]#pname:codedExtent.width# rounded up to the
    nearest integer multiple of pname:pictureAccessGranularity.width and
    clamped to the width of the image subresource
    <<video-image-subresource-reference,referred>> to by the corresponding
    slink:VkVideoPictureResourceInfoKHR structure;
  * [eq]#endY# equals [eq]#pname:codedExtent.height# rounded up to the
    nearest integer multiple of pname:pictureAccessGranularity.height and
    clamped to the height of the image subresource
    <<video-image-subresource-reference,referred>> to by the corresponding
    slink:VkVideoPictureResourceInfoKHR structure;

Where pname:codedExtent is the member of the
slink:VkVideoPictureResourceInfoKHR structure corresponding to the picture.

In case of video encode operations using an <<encode-h264-profile,H.264
encode profile>>, any access to a picture at the coordinates
[eq]#(pname:x,pname:y)#, as defined by the <<itu-t-h264,ITU-T H.264
Specification>>, is an access to the image subresource
<<video-image-subresource-reference,referred>> to by the corresponding
slink:VkVideoPictureResourceInfoKHR structure at the texel coordinates
[eq]#(pname:x,pname:y)#.

Implementations may: choose not to access some or all texels within
particular <<reference-picture,reference pictures>> available to a video
encode operation (e.g. due to <<encode-overrides,video encode parameter
overrides>> restricting the effective set of used reference pictures, or if
the encoding algorithm chooses not to use certain subregions of the
reference picture data for sample prediction).


[[encode-h264-frame-picture-slice]]
=== H.264 Frame, Picture, and Slice

H.264 pictures are partitioned into slices, as defined in section 6.3 of the
<<itu-t-h264,ITU-T H.264 Specification>>.

Video encode operations using an <<encode-h264-profile,H.264 encode
profile>> can: encode slices of different types, as defined in section 7.4.3
of the <<itu-t-h264,ITU-T H.264 Specification>>, by specifying the
corresponding enumeration constant value in
code:StdVideoEncodeH264SliceHeader::code:slice_type in the
<<encode-h264-slice-header-params,H.264 slice header parameters>> from the
Video Std enumeration type code:StdVideoH264SliceType:

  * [[encode-h264-p-slice]] code:STD_VIDEO_H264_SLICE_TYPE_P indicates that
    the slice is a _P slice_ as defined in section 3.109 of the
    <<itu-t-h264,ITU-T H.264 Specification>>.
  * [[encode-h264-b-slice]] code:STD_VIDEO_H264_SLICE_TYPE_B indicates that
    the slice is a _B slice_ as defined in section 3.9 of the
    <<itu-t-h264,ITU-T H.264 Specification>>.
  * [[encode-h264-i-slice]] code:STD_VIDEO_H264_SLICE_TYPE_I indicates that
    the slice is an _I slice_ as defined in section 3.66 of the
    <<itu-t-h264,ITU-T H.264 Specification>>.

Pictures constructed from such slices can: be of different types, as defined
in section 7.4.2.4 of the <<itu-t-h264,ITU-T H.264 Specification>>.
Video encode operations using an <<encode-h264-profile,H.264 encode
profile>> can: encode pictures of a specific type by specifying the
corresponding enumeration constant value in
code:StdVideoEncodeH264PictureInfo::code:primary_pic_type in the
<<encode-h264-picture-info,H.264 picture information>> from the Video Std
enumeration type code:StdVideoH264PictureType:

  * [[encode-h264-p-pic]] code:STD_VIDEO_H264_PICTURE_TYPE_P indicates that
    the picture is a _P picture_.
    A frame consisting of a P picture is also referred to as a _P frame_.
  * [[encode-h264-b-pic]] code:STD_VIDEO_H264_PICTURE_TYPE_B indicates that
    the picture is a _B picture_.
    A frame consisting of a B picture is also referred to as a _B frame_.
  * [[encode-h264-i-pic]] code:STD_VIDEO_H264_PICTURE_TYPE_I indicates that
    the picture is an _I picture_.
    A frame consisting of an I picture is also referred to as an _I frame_.
  * [[encode-h264-idr-pic]] code:STD_VIDEO_H264_PICTURE_TYPE_IDR indicates
    that the picture is a special type of I picture called an _IDR picture_
    as defined in section 3.69 of the <<itu-t-h264,ITU-T H.264
    Specification>>.
    A frame consisting of an IDR picture is also referred to as an _IDR
    frame_.


[[encode-h264-profile]]
=== H.264 Encode Profile

[open,refpage='VkVideoEncodeH264ProfileInfoKHR',desc='Structure specifying H.264 encode-specific video profile parameters',type='structs']
--
A video profile supporting H.264 video encode operations is specified by
setting slink:VkVideoProfileInfoKHR::pname:videoCodecOperation to
ename:VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR and adding a
sname:VkVideoEncodeH264ProfileInfoKHR structure to the
slink:VkVideoProfileInfoKHR::pname:pNext chain.

The sname:VkVideoEncodeH264ProfileInfoKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264ProfileInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:stdProfileIdc is a code:StdVideoH264ProfileIdc value specifying
    the H.264 codec profile IDC, as defined in section A.2 of the
    <<itu-t-h264,ITU-T H.264 Specification>>.

include::{generated}/validity/structs/VkVideoEncodeH264ProfileInfoKHR.adoc[]
--


=== H.264 Encode Capabilities

[open,refpage='VkVideoEncodeH264CapabilitiesKHR',desc='Structure describing H.264 encode capabilities',type='structs']
--
When calling flink:vkGetPhysicalDeviceVideoCapabilitiesKHR to query the
capabilities for an <<encode-h264-profile,H.264 encode profile>>, the
slink:VkVideoCapabilitiesKHR::pname:pNext chain must: include a
sname:VkVideoEncodeH264CapabilitiesKHR structure that will be filled with
the profile-specific capabilities.

The sname:VkVideoEncodeH264CapabilitiesKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264CapabilitiesKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:flags is a bitmask of elink:VkVideoEncodeH264CapabilityFlagBitsKHR
    indicating supported H.264 encoding capabilities.
  * pname:maxLevelIdc is a code:StdVideoH264LevelIdc value indicating the
    maximum H.264 level supported by the profile, where enum constant
    `STD_VIDEO_H264_LEVEL_IDC_<major>_<minor>` identifies H.264 level
    `<major>.<minor>` as defined in section A.3 of the <<itu-t-h264,ITU-T
    H.264 Specification>>.
  * pname:maxSliceCount indicates the maximum number of slices that can: be
    encoded for a single picture.
    Further restrictions may: apply to the number of slices that can: be
    encoded for a single picture depending on other capabilities and
    codec-specific rules.
  * pname:maxPPictureL0ReferenceCount indicates the maximum number of
    reference pictures the implementation supports in the reference list L0
    for <<encode-h264-p-pic,P pictures>>.
+
[NOTE]
.Note
====
As implementations may: <<encode-overrides,override>> the reference lists,
pname:maxPPictureL0ReferenceCount does not limit the number of elements that
the application can: specify in the L0 reference list for P pictures.
However, if pname:maxPPictureL0ReferenceCount is zero, then the use of P
pictures is not allowed.
====
  * pname:maxBPictureL0ReferenceCount indicates the maximum number of
    reference pictures the implementation supports in the reference list L0
    for <<encode-h264-b-pic,B pictures>>.
  * pname:maxL1ReferenceCount indicates the maximum number of reference
    pictures the implementation supports in the reference list L1 if
    encoding of <<encode-h264-b-pic,B pictures>> is supported.
+
[NOTE]
.Note
====
As implementations may: <<encode-overrides,override>> the reference lists,
pname:maxBPictureL0ReferenceCount and pname:maxL1ReferenceCount does not
limit the number of elements that the application can: specify in the L0 and
L1 reference lists for B pictures.
However, if pname:maxBPictureL0ReferenceCount and pname:maxL1ReferenceCount
are both zero, then the use of B pictures is not allowed.
====
  * pname:maxTemporalLayerCount indicates the maximum number of H.264
    temporal layers supported by the implementation.
  * pname:expectDyadicTemporalLayerPattern indicates that the
    implementation's rate control algorithms expect the application to use a
    <<encode-h264-layer-pattern-dyadic,dyadic temporal layer pattern>> when
    encoding multiple temporal layers.
  * pname:minQp indicates the minimum QP value supported.
  * pname:maxQp indicates the maximum QP value supported.
  * pname:prefersGopRemainingFrames indicates that the implementation's rate
    control algorithm prefers the application to specify the number of
    frames of each type <<encode-h264-gop-remaining-frames,remaining>> in
    the current <<encode-h264-gop,group of pictures>> when beginning a
    <<video-coding-scope,video coding scope>>.
  * pname:requiresGopRemainingFrames indicates that the implementation's
    rate control algorithm requires the application to specify the number of
    frames of each type <<encode-h264-gop-remaining-frames,remaining>> in
    the current <<encode-h264-gop,group of pictures>> when beginning a
    <<video-coding-scope,video coding scope>>.
  * pname:stdSyntaxFlags is a bitmask of
    elink:VkVideoEncodeH264StdFlagBitsKHR indicating capabilities related to
    H.264 syntax elements.

include::{generated}/validity/structs/VkVideoEncodeH264CapabilitiesKHR.adoc[]
--


[open,refpage='VkVideoEncodeH264CapabilityFlagBitsKHR',desc='H.264 encode capability flags',type='enums']
--
Bits which may: be set in
slink:VkVideoEncodeH264CapabilitiesKHR::pname:flags, indicating the H.264
encoding capabilities supported, are:

include::{generated}/api/enums/VkVideoEncodeH264CapabilityFlagBitsKHR.adoc[]

  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_HRD_COMPLIANCE_BIT_KHR indicates
    whether the implementation may: be able to generate HRD compliant
    bitstreams if any of the code:nal_hrd_parameters_present_flag or
    code:vcl_hrd_parameters_present_flag members of
    code:StdVideoH264SpsVuiFlags are set to `1` in the
    <<encode-h264-active-sps,active SPS>>.
  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_PREDICTION_WEIGHT_TABLE_GENERATED_BIT_KHR
    indicates that if code:StdVideoH264PpsFlags::code:weighted_pred_flag is
    set to `1` or
    code:StdVideoH264PictureParameterSet::code:weighted_bipred_idc is set to
    code:STD_VIDEO_H264_WEIGHTED_BIPRED_IDC_EXPLICIT in the
    <<encode-h264-active-pps,active PPS>> when encoding a
    <<encode-h264-p-pic,P picture>> or <<encode-h264-b-pic,B picture>>,
    respectively, then the implementation is able to internally decide
    syntax for code:pred_weight_table, as defined in section 7.4.3.2 of the
    <<itu-t-h264,ITU-T H.264 Specification>>, and the application is not
    required: to provide a weight table in the
    <<encode-h264-slice-header-params,H.264 slice header parameters>>.
  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_ROW_UNALIGNED_SLICE_BIT_KHR
    indicates that each slice in a frame with multiple slices may begin or
    finish at any offset in a macroblock row.
    If not supported, all slices in the frame must: begin at the start of a
    macroblock row (and hence each slice must: finish at the end of a
    macroblock row).
  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_DIFFERENT_SLICE_TYPE_BIT_KHR
    indicates that when a frame is encoded with multiple slices, the
    implementation allows encoding each slice with a different
    code:StdVideoEncodeH264SliceHeader::code:slice_type specified in the
    <<encode-h264-slice-header-params,H.264 slice header parameters>>.
    If not supported, all slices of the frame must: be encoded with the same
    code:slice_type which corresponds to the picture type of the frame.
  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_B_FRAME_IN_L0_LIST_BIT_KHR
    indicates support for using a <<encode-h264-b-pic,B frame>> as L0
    reference, as specified in
    code:StdVideoEncodeH264ReferenceListsInfo::code:RefPicList0 in the
    <<encode-h264-picture-info,H.264 picture information>>.
  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_B_FRAME_IN_L1_LIST_BIT_KHR
    indicates support for using a <<encode-h264-b-pic,B frame>> as L1
    reference, as specified in
    code:StdVideoEncodeH264ReferenceListsInfo::code:RefPicList1 in the
    <<encode-h264-picture-info,H.264 picture information>>.
  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_PER_PICTURE_TYPE_MIN_MAX_QP_BIT_KHR
    indicates support for specifying different QP values in the members of
    slink:VkVideoEncodeH264QpKHR.
  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_PER_SLICE_CONSTANT_QP_BIT_KHR
    indicates support for specifying different constant QP values for each
    slice.
  * ename:VK_VIDEO_ENCODE_H264_CAPABILITY_GENERATE_PREFIX_NALU_BIT_KHR
    indicates support for generating prefix NAL units by setting
    slink:VkVideoEncodeH264PictureInfoKHR::pname:generatePrefixNalu to
    ename:VK_TRUE.
--

[open,refpage='VkVideoEncodeH264CapabilityFlagsKHR',desc='Bitmask of VkVideoEncodeH264CapabilityFlagBitsKHR',type='flags']
--
include::{generated}/api/flags/VkVideoEncodeH264CapabilityFlagsKHR.adoc[]

tname:VkVideoEncodeH264CapabilityFlagsKHR is a bitmask type for setting a
mask of zero or more elink:VkVideoEncodeH264CapabilityFlagBitsKHR.
--

[open,refpage='VkVideoEncodeH264StdFlagBitsKHR',desc='Video encode H.264 syntax capability flags',type='enums']
--
Bits which may: be set in
slink:VkVideoEncodeH264CapabilitiesKHR::pname:stdSyntaxFlags, indicating the
capabilities related to the H.264 syntax elements, are:

include::{generated}/api/enums/VkVideoEncodeH264StdFlagBitsKHR.adoc[]

  * ename:VK_VIDEO_ENCODE_H264_STD_SEPARATE_COLOR_PLANE_FLAG_SET_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoH264SpsFlags::code:separate_colour_plane_flag in the
    <<encode-h264-sps,SPS>> when that value is `1`.
  * ename:VK_VIDEO_ENCODE_H264_STD_QPPRIME_Y_ZERO_TRANSFORM_BYPASS_FLAG_SET_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoH264SpsFlags::code:qpprime_y_zero_transform_bypass_flag in
    the <<encode-h264-sps,SPS>> when that value is `1`.
  * ename:VK_VIDEO_ENCODE_H264_STD_SCALING_MATRIX_PRESENT_FLAG_SET_BIT_KHR
    indicates whether the implementation supports using the
    application-provided values for
    code:StdVideoH264SpsFlags::code:seq_scaling_matrix_present_flag in the
    <<encode-h264-sps,SPS>> and
    code:StdVideoH264PpsFlags::code:pic_scaling_matrix_present_flag in the
    <<encode-h264-pps,PPS>> when any of those values are `1`.
  * ename:VK_VIDEO_ENCODE_H264_STD_CHROMA_QP_INDEX_OFFSET_BIT_KHR indicates
    whether the implementation supports using the application-provided value
    for code:StdVideoH264PictureParameterSet::code:chroma_qp_index_offset in
    the <<encode-h264-pps,PPS>> when that value is non-zero.
  * ename:VK_VIDEO_ENCODE_H264_STD_SECOND_CHROMA_QP_INDEX_OFFSET_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoH264PictureParameterSet::code:second_chroma_qp_index_offset
    in the <<encode-h264-pps,PPS>> when that value is non-zero.
  * ename:VK_VIDEO_ENCODE_H264_STD_PIC_INIT_QP_MINUS26_BIT_KHR indicates
    whether the implementation supports using the application-provided value
    for code:StdVideoH264PictureParameterSet::code:pic_init_qp_minus26 in
    the <<encode-h264-pps,PPS>> when that value is non-zero.
  * ename:VK_VIDEO_ENCODE_H264_STD_WEIGHTED_PRED_FLAG_SET_BIT_KHR indicates
    whether the implementation supports using the application-provided value
    for code:StdVideoH264PpsFlags::code:weighted_pred_flag in the
    <<encode-h264-pps,PPS>> when that value is `1`.
  * ename:VK_VIDEO_ENCODE_H264_STD_WEIGHTED_BIPRED_IDC_EXPLICIT_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoH264PictureParameterSet::code:weighted_bipred_idc in the
    <<encode-h264-pps,PPS>> when that value is
    code:STD_VIDEO_H264_WEIGHTED_BIPRED_IDC_EXPLICIT.
  * ename:VK_VIDEO_ENCODE_H264_STD_WEIGHTED_BIPRED_IDC_IMPLICIT_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoH264PictureParameterSet::code:weighted_bipred_idc in the
    <<encode-h264-pps,PPS>> when that value is
    code:STD_VIDEO_H264_WEIGHTED_BIPRED_IDC_IMPLICIT.
  * ename:VK_VIDEO_ENCODE_H264_STD_TRANSFORM_8X8_MODE_FLAG_SET_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoH264PpsFlags::code:transform_8x8_mode_flag in the
    <<encode-h264-pps,PPS>> when that value is `1`.
  * ename:VK_VIDEO_ENCODE_H264_STD_DIRECT_SPATIAL_MV_PRED_FLAG_UNSET_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoEncodeH264SliceHeaderFlags::code:direct_spatial_mv_pred_flag
    in the <<encode-h264-slice-header-params,H.264 slice header parameters>>
    when that value is `0`.
  * ename:VK_VIDEO_ENCODE_H264_STD_ENTROPY_CODING_MODE_FLAG_UNSET_BIT_KHR
    indicates whether the implementation supports CAVLC entropy coding, as
    defined in section 9.2 of the <<itu-t-h264,ITU-T H.264 Specification>>,
    and thus supports using the application-provided value for
    code:StdVideoH264PpsFlags::code:entropy_coding_mode_flag in the
    <<encode-h264-pps,PPS>> when that value is `0`.
  * ename:VK_VIDEO_ENCODE_H264_STD_ENTROPY_CODING_MODE_FLAG_SET_BIT_KHR
    indicates whether the implementation supports CABAC entropy coding, as
    defined in section 9.3 of the <<itu-t-h264,ITU-T H.264 Specification>>,
    and thus supports using the application-provided value for
    code:StdVideoH264PpsFlags::code:entropy_coding_mode_flag in the
    <<encode-h264-pps,PPS>> when that value is `1`.
  * ename:VK_VIDEO_ENCODE_H264_STD_DIRECT_8X8_INFERENCE_FLAG_UNSET_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoH264SpsFlags::code:direct_8x8_inference_flag in the
    <<encode-h264-sps,SPS>> when that value is `0`.
  * ename:VK_VIDEO_ENCODE_H264_STD_CONSTRAINED_INTRA_PRED_FLAG_SET_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoH264PpsFlags::code:constrained_intra_pred_flag in the
    <<encode-h264-pps,PPS>> when that value is `1`.
  * ename:VK_VIDEO_ENCODE_H264_STD_DEBLOCKING_FILTER_DISABLED_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoEncodeH264SliceHeader::code:disable_deblocking_filter_idc
    in the <<encode-h264-slice-header-params,H.264 slice header parameters>>
    when that value is
    code:STD_VIDEO_H264_DISABLE_DEBLOCKING_FILTER_IDC_DISABLED.
  * ename:VK_VIDEO_ENCODE_H264_STD_DEBLOCKING_FILTER_ENABLED_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoEncodeH264SliceHeader::code:disable_deblocking_filter_idc
    in the <<encode-h264-slice-header-params,H.264 slice header parameters>>
    when that value is
    code:STD_VIDEO_H264_DISABLE_DEBLOCKING_FILTER_IDC_ENABLED.
  * ename:VK_VIDEO_ENCODE_H264_STD_DEBLOCKING_FILTER_PARTIAL_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoEncodeH264SliceHeader::code:disable_deblocking_filter_idc
    in the <<encode-h264-slice-header-params,H.264 slice header parameters>>
    when that value is
    code:STD_VIDEO_H264_DISABLE_DEBLOCKING_FILTER_IDC_PARTIAL.
  * ename:VK_VIDEO_ENCODE_H264_STD_SLICE_QP_DELTA_BIT_KHR indicates whether
    the implementation supports using the application-provided value for
    code:StdVideoEncodeH264SliceHeader::code:slice_qp_delta in the
    <<encode-h264-slice-header-params,H.264 slice header parameters>> when
    that value is identical across the slices of the encoded frame.
  * ename:VK_VIDEO_ENCODE_H264_STD_DIFFERENT_SLICE_QP_DELTA_BIT_KHR
    indicates whether the implementation supports using the
    application-provided value for
    code:StdVideoEncodeH264SliceHeader::code:slice_qp_delta in the
    <<encode-h264-slice-header-params,H.264 slice header parameters>> when
    that value is different across the slices of the encoded frame.

These capability flags provide information to the application about specific
H.264 syntax element values that the implementation supports without having
to <<encode-h264-overrides,override>> them and do not otherwise restrict the
values that the application can: specify for any of the mentioned H.264
syntax elements.
--

[open,refpage='VkVideoEncodeH264StdFlagsKHR',desc='Bitmask of VkVideoEncodeH264StdFlagBitsKHR',type='flags']
--
include::{generated}/api/flags/VkVideoEncodeH264StdFlagsKHR.adoc[]

tname:VkVideoEncodeH264StdFlagsKHR is a bitmask type for setting a mask of
zero or more elink:VkVideoEncodeH264StdFlagBitsKHR.
--


=== H.264 Encode Quality Level Properties

[open,refpage='VkVideoEncodeH264QualityLevelPropertiesKHR',desc='Structure describing the H.264 encode quality level properties',type='structs']
--
When calling flink:vkGetPhysicalDeviceVideoEncodeQualityLevelPropertiesKHR
with pname:pVideoProfile->videoCodecOperation specified as
ename:VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR, the
slink:VkVideoEncodeH264QualityLevelPropertiesKHR structure must: be included
in the pname:pNext chain of the slink:VkVideoEncodeQualityLevelPropertiesKHR
structure to retrieve additional video encode quality level properties
specific to H.264 encoding.

The slink:VkVideoEncodeH264QualityLevelPropertiesKHR structure is defined
as:

include::{generated}/api/structs/VkVideoEncodeH264QualityLevelPropertiesKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:preferredRateControlFlags is a bitmask of
    elink:VkVideoEncodeH264RateControlFlagBitsKHR values indicating the
    preferred flags to use for
    slink:VkVideoEncodeH264RateControlInfoKHR::pname:flags.
  * pname:preferredGopFrameCount indicates the preferred value to use for
    slink:VkVideoEncodeH264RateControlInfoKHR::pname:gopFrameCount.
  * pname:preferredIdrPeriod indicates the preferred value to use for
    slink:VkVideoEncodeH264RateControlInfoKHR::pname:idrPeriod.
  * pname:preferredConsecutiveBFrameCount indicates the preferred value to
    use for
    slink:VkVideoEncodeH264RateControlInfoKHR::pname:consecutiveBFrameCount.
  * pname:preferredTemporalLayerCount indicates the preferred value to use
    for slink:VkVideoEncodeH264RateControlInfoKHR::pname:temporalLayerCount.
  * pname:preferredConstantQp indicates the preferred values to use for
    slink:VkVideoEncodeH264NaluSliceInfoKHR::pname:constantQp for each
    picture type when using <<encode-rate-control-modes,rate control mode>>
    ename:VK_VIDEO_ENCODE_RATE_CONTROL_MODE_DISABLED_BIT_KHR.
  * pname:preferredMaxL0ReferenceCount indicates the preferred maximum
    number of reference pictures to use in the reference list L0.
  * pname:preferredMaxL1ReferenceCount indicates the preferred maximum
    number of reference pictures to use in the reference list L1.
  * pname:preferredStdEntropyCodingModeFlag indicates the preferred value to
    use for code:entropy_coding_mode_flag in code:StdVideoH264PpsFlags.

include::{generated}/validity/structs/VkVideoEncodeH264QualityLevelPropertiesKHR.adoc[]
--


=== H.264 Encode Session

Additional parameters can be specified when creating a video session with an
H.264 encode profile by including an instance of the
slink:VkVideoEncodeH264SessionCreateInfoKHR structure in the pname:pNext
chain of slink:VkVideoSessionCreateInfoKHR.

[open,refpage='VkVideoEncodeH264SessionCreateInfoKHR',desc='Structure specifies H.264 encode session parameters',type='structs']
--
The sname:VkVideoEncodeH264SessionCreateInfoKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264SessionCreateInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:useMaxLevelIdc indicates whether the value of pname:maxLevelIdc
    should be used by the implementation.
    When it is set to ename:VK_FALSE, the implementation ignores the value
    of pname:maxLevelIdc and uses the value of
    slink:VkVideoEncodeH264CapabilitiesKHR::pname:maxLevelIdc, as reported
    by flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the video profile.
  * pname:maxLevelIdc is a code:StdVideoH264LevelIdc value specifying the
    upper bound on the H.264 level for the video bitstreams produced by the
    created video session, where enum constant
    `STD_VIDEO_H264_LEVEL_IDC_<major>_<minor>` identifies H.264 level
    `<major>.<minor>` as defined in section A.3 of the <<itu-t-h264,ITU-T
    H.264 Specification>>.

include::{generated}/validity/structs/VkVideoEncodeH264SessionCreateInfoKHR.adoc[]
--


[[encode-h264-parameter-sets]]
=== H.264 Encode Parameter Sets

<<video-session-parameters,Video session parameters>> objects created with
the video codec operation ename:VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR
can: contain the following types of parameters:

:operationType: encode
include::{chapters}/video/h264_parameter_sets.adoc[]

Implementations may: override any of these parameters according to the
semantics defined in the <<encode-overrides,Video Encode Parameter
Overrides>> section before storing the resulting H.264 parameter sets into
the video session parameters object.
Applications need to use the flink:vkGetEncodedVideoSessionParametersKHR
command to determine whether any implementation overrides happened and to
retrieve the encoded H.264 parameter sets in order to be able to produce a
compliant H.264 video bitstream.

Such H.264 parameter set overrides may: also have cascading effects on the
implementation overrides applied to the encoded bitstream produced by video
encode operations.
If the implementation supports the
ename:VK_VIDEO_ENCODE_FEEDBACK_BITSTREAM_HAS_OVERRIDES_BIT_KHR
<<queries-video-encode-feedback,video encode feedback query>> flag, then the
application can: use such queries to retrieve feedback about whether any
implementation overrides have been applied to the encoded bitstream.

[open,refpage='VkVideoEncodeH264SessionParametersCreateInfoKHR',desc='Structure specifies H.264 encoder parameter set information',type='structs']
--
When a <<video-session-parameters,video session parameters>> object is
created with the codec operation
ename:VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR, the
slink:VkVideoSessionParametersCreateInfoKHR::pname:pNext chain must: include
a sname:VkVideoEncodeH264SessionParametersCreateInfoKHR structure specifying
the capacity and initial contents of the object.

The sname:VkVideoEncodeH264SessionParametersCreateInfoKHR structure is
defined as:

include::{generated}/api/structs/VkVideoEncodeH264SessionParametersCreateInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:maxStdSPSCount is the maximum number of <<encode-h264-sps,H.264
    SPS>> entries the created sname:VkVideoSessionParametersKHR can:
    contain.
  * pname:maxStdPPSCount is the maximum number of <<encode-h264-pps,H.264
    PPS>> entries the created sname:VkVideoSessionParametersKHR can:
    contain.
  * pname:pParametersAddInfo is `NULL` or a pointer to a
    slink:VkVideoEncodeH264SessionParametersAddInfoKHR structure specifying
    H.264 parameters to add upon object creation.

include::{generated}/validity/structs/VkVideoEncodeH264SessionParametersCreateInfoKHR.adoc[]
--

[open,refpage='VkVideoEncodeH264SessionParametersAddInfoKHR',desc='Structure specifies H.264 encoder parameter set information',type='structs']
--
The sname:VkVideoEncodeH264SessionParametersAddInfoKHR structure is defined
as:

include::{generated}/api/structs/VkVideoEncodeH264SessionParametersAddInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:stdSPSCount is the number of elements in the pname:pStdSPSs array.
  * pname:pStdSPSs is a pointer to an array of
    code:StdVideoH264SequenceParameterSet structures describing the
    <<encode-h264-sps,H.264 SPS>> entries to add.
  * pname:stdPPSCount is the number of elements in the pname:pStdPPSs array.
  * pname:pStdPPSs is a pointer to an array of
    code:StdVideoH264PictureParameterSet structures describing the
    <<encode-h264-pps,H.264 PPS>> entries to add.

This structure can: be specified in the following places:

  * In the pname:pParametersAddInfo member of the
    slink:VkVideoEncodeH264SessionParametersCreateInfoKHR structure
    specified in the pname:pNext chain of
    slink:VkVideoSessionParametersCreateInfoKHR used to create a
    <<video-session-parameters,video session parameters>> object.
    In this case, if the video codec operation the video session parameters
    object is created with is
    ename:VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR, then it defines the
    set of initial parameters to add to the created object (see
    <<creating-video-session-parameters,Creating Video Session
    Parameters>>).
  * In the pname:pNext chain of slink:VkVideoSessionParametersUpdateInfoKHR.
    In this case, if the video codec operation the
    <<video-session-parameters,video session parameters>> object to be
    updated was created with is
    ename:VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR, then it defines the
    set of parameters to add to it (see
    <<video-session-parameters-update,Updating Video Session Parameters>>).

.Valid Usage
****
  * [[VUID-VkVideoEncodeH264SessionParametersAddInfoKHR-None-04837]]
    The pname:seq_parameter_set_id member of each
    code:StdVideoH264SequenceParameterSet structure specified in the
    elements of pname:pStdSPSs must: be unique within pname:pStdSPSs
  * [[VUID-VkVideoEncodeH264SessionParametersAddInfoKHR-None-04838]]
    The pair constructed from the pname:seq_parameter_set_id and
    pname:pic_parameter_set_id members of each
    code:StdVideoH264PictureParameterSet structure specified in the elements
    of pname:pStdPPSs must: be unique within pname:pStdPPSs
****

include::{generated}/validity/structs/VkVideoEncodeH264SessionParametersAddInfoKHR.adoc[]
--

[open,refpage='VkVideoEncodeH264SessionParametersGetInfoKHR',desc='Structure specifying parameters for retrieving encoded H.264 parameter set data',type='structs']
--
The sname:VkVideoEncodeH264SessionParametersGetInfoKHR structure is defined
as:

include::{generated}/api/structs/VkVideoEncodeH264SessionParametersGetInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:writeStdSPS indicates whether the encoded <<encode-h264-sps,H.264
    sequence parameter set>> identified by pname:stdSPSId is requested to be
    retrieved.
  * pname:writeStdPPS indicates whether the encoded <<encode-h264-pps,H.264
    picture parameter set>> identified by the pair constructed from
    pname:stdSPSId and pname:stdPPSId is requested to be retrieved.
  * pname:stdSPSId specifies the H.264 sequence parameter set ID used to
    identify the retrieved H.264 sequence and/or picture parameter set(s).
  * pname:stdPPSId specifies the H.264 picture parameter set ID used to
    identify the retrieved H.264 picture parameter set when
    pname:writeStdPPS is set to ename:VK_TRUE.

When this structure is specified in the pname:pNext chain of the
slink:VkVideoEncodeSessionParametersGetInfoKHR structure passed to
flink:vkGetEncodedVideoSessionParametersKHR, the command will write encoded
parameter data to the output buffer in the following order:

  . The <<encode-h264-sps,H.264 sequence parameter set>> identified by
    pname:stdSPSId, if pname:writeStdSPS is set to ename:VK_TRUE.
  . The <<encode-h264-pps,H.264 picture parameter set>> identified by the
    pair constructed from pname:stdSPSId and pname:stdPPSId, if
    pname:writeStdPPS is set to ename:VK_TRUE.

.Valid Usage
****
  * [[VUID-VkVideoEncodeH264SessionParametersGetInfoKHR-writeStdSPS-08279]]
    At least one of pname:writeStdSPS and pname:writeStdPPS must: be set to
    ename:VK_TRUE
****

include::{generated}/validity/structs/VkVideoEncodeH264SessionParametersGetInfoKHR.adoc[]
--

[open,refpage='VkVideoEncodeH264SessionParametersFeedbackInfoKHR',desc='Structure providing feedback about the requested H.264 video session parameters',type='structs']
--
The sname:VkVideoEncodeH264SessionParametersFeedbackInfoKHR structure is
defined as:

include::{generated}/api/structs/VkVideoEncodeH264SessionParametersFeedbackInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:hasStdSPSOverrides indicates whether any of the parameters of the
    requested <<encode-h264-sps,H.264 sequence parameter set>>, if one was
    requested via
    slink:VkVideoEncodeH264SessionParametersGetInfoKHR::pname:writeStdSPS,
    were <<encode-overrides,overridden>> by the implementation.
  * pname:hasStdPPSOverrides indicates whether any of the parameters of the
    requested <<encode-h264-pps,H.264 picture parameter set>>, if one was
    requested via
    slink:VkVideoEncodeH264SessionParametersGetInfoKHR::pname:writeStdPPS,
    were <<encode-overrides,overridden>> by the implementation.

include::{generated}/validity/structs/VkVideoEncodeH264SessionParametersFeedbackInfoKHR.adoc[]
--

=== H.264 Encoding Parameters

[open,refpage='VkVideoEncodeH264PictureInfoKHR',desc='Structure specifies H.264 encode frame parameters',type='structs']
--
The slink:VkVideoEncodeH264PictureInfoKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264PictureInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:naluSliceEntryCount is the number of elements in
    pname:pNaluSliceEntries.
  * pname:pNaluSliceEntries is a pointer to an array of
    pname:naluSliceEntryCount slink:VkVideoEncodeH264NaluSliceInfoKHR
    structures specifying the parameters of the individual H.264 slices to
    encode for the input picture.
  * pname:pStdPictureInfo is a pointer to a
    code:StdVideoEncodeH264PictureInfo structure specifying
    <<encode-h264-picture-info,H.264 picture information>>.
  * pname:generatePrefixNalu controls whether prefix NALUs are generated
    before slice NALUs into the target bitstream, as defined in sections
    7.3.2.12 and 7.4.2.12 of the <<itu-t-h264,ITU-T H.264 Specification>>.

This structure is specified in the pname:pNext chain of the
slink:VkVideoEncodeInfoKHR structure passed to flink:vkCmdEncodeVideoKHR to
specify the codec-specific picture information for an <<encode-h264,H.264
encode operation>>.

[[encode-h264-input-picture-info]]
Encode Input Picture Information::

When this structure is specified in the pname:pNext chain of the
slink:VkVideoEncodeInfoKHR structure passed to flink:vkCmdEncodeVideoKHR,
the information related to the <<encode-input-picture-info,encode input
picture>> is defined as follows:

  * The image subregion used is determined according to the
    <<encode-h264-picture-data-access,H.264 Encode Picture Data Access>>
    section.
  * The encode input picture is associated with the
    <<encode-h264-picture-info,H.264 picture information>> provided in
    pname:pStdPictureInfo.

[[encode-h264-picture-info]]
Std Picture Information::

The members of the code:StdVideoEncodeH264PictureInfo structure pointed to
by pname:pStdPictureInfo are interpreted as follows:

  * code:flags.reserved and code:reserved1 are used only for padding
    purposes and are otherwise ignored;
  * code:flags.IdrPicFlag as defined in section 7.4.1 of the <<itu-t-h264,
    ITU-T H.264 Specification>>;
  * code:flags.is_reference as defined in section 3.136 of the <<itu-t-h264,
    ITU-T H.264 Specification>>;
  * code:seq_parameter_set_id and code:pic_parameter_set_id are used to
    identify the active parameter sets, as described below;
  * code:primary_pic_type as defined in section 7.4.2 of the <<itu-t-h264,
    ITU-T H.264 Specification>>;
  * code:PicOrderCnt as defined in section 8.2 of the <<itu-t-h264,ITU-T
    H.264 Specification>>;
  * code:temporal_id as defined in section G.7.4.1.1 of the <<itu-t-h264,
    ITU-T H.264 Specification>>;
  * if code:pRefLists is not `NULL`, then it is a pointer to a
    code:StdVideoEncodeH264ReferenceListsInfo structure that is interpreted
    as follows:
  ** code:flags.reserved is used only for padding purposes and is otherwise
     ignored;
  ** code:ref_pic_list_modification_flag_l0 and
     code:ref_pic_list_modification_flag_l1 as defined in section 7.4.3.1 of
     the <<itu-t-h264, ITU-T H.264 Specification>>;
  ** code:num_ref_idx_l0_active_minus1 and code:num_ref_idx_l1_active_minus1
     as defined in section 7.4.3 of the <<itu-t-h264, ITU-T H.264
     Specification>>;
  ** code:RefPicList0 and code:RefPicList1 as defined in section 8.2.4 of
     the <<itu-t-h264, ITU-T H.264 Specification>> where each element of
     these arrays either identifies an
     <<encode-active-reference-picture-info,active reference picture>> using
     its <<dpb-slot,DPB slot>> index or contains the value
     code:STD_VIDEO_H264_NO_REFERENCE_PICTURE to indicate "`no reference
     picture`";
  ** if code:refList0ModOpCount is not zero, then
     code:pRefList0ModOperations is a pointer to an array of
     code:refList0ModOpCount number of
     code:StdVideoEncodeH264RefListModEntry structures specifying the
     modification parameters for the reference list L0 as defined in section
     7.4.3.1 of the <<itu-t-h264, ITU-T H.264 Specification>>;
  ** if code:refList1ModOpCount is not zero, then
     code:pRefList1ModOperations is a pointer to an array of
     code:refList1ModOpCount number of
     code:StdVideoEncodeH264RefListModEntry structures specifying the
     modification parameters for the reference list L1 as defined in section
     7.4.3.1 of the <<itu-t-h264, ITU-T H.264 Specification>>;
  ** if code:refPicMarkingOpCount is not zero, then
     code:refPicMarkingOperations is a pointer to an array of
     code:refPicMarkingOpCount number of
     code:StdVideoEncodeH264RefPicMarkingEntry structures specifying the
     reference picture marking parameters as defined in section 7.4.3.3 of
     the <<itu-t-h264, ITU-T H.264 Specification>>;
  * all other members are interpreted as defined in section 7.4.3 of the
    <<itu-t-h264,ITU-T H.264 Specification>>.

[[encode-h264-ref-pic-setup]]
Reference picture setup is controlled by the value of
code:StdVideoEncodeH264PictureInfo::pname:flags.is_reference.
If it is set and a <<encode-reconstructed-picture-info,reconstructed
picture>> is specified, then the latter is used as the target of picture
reconstruction to <<dpb-slot-states,activate>> the <<dpb-slot,DPB slot>>
specified in pname:pEncodeInfo->pSetupReferenceSlot->slotIndex.
If code:StdVideoEncodeH264PictureInfo::pname:flags.is_reference is not set,
but a <<encode-reconstructed-picture-info,reconstructed picture>> is
specified, then the corresponding picture reference associated with the
<<dpb-slot,DPB slot>> is invalidated, as described in the
<<dpb-slot-states,DPB Slot States>> section.

Active Parameter Sets::

The members of the code:StdVideoEncodeH264PictureInfo structure pointed to
by pname:pStdPictureInfo are used to select the active parameter sets to use
from the bound video session parameters object, as follows:

  * [[encode-h264-active-sps]] The _active SPS_ is the
    <<encode-h264-sps,SPS>> identified by the key specified in
    code:StdVideoEncodeH264PictureInfo::code:seq_parameter_set_id.
  * [[encode-h264-active-pps]] The _active PPS_ is the
    <<encode-h264-pps,PPS>> identified by the key specified by the pair
    constructed from
    code:StdVideoEncodeH264PictureInfo::code:seq_parameter_set_id and
    code:StdVideoEncodeH264PictureInfo::code:pic_parameter_set_id.

[[encode-h264-weighted-pred]]
H.264 encoding uses _explicit weighted sample prediction_ for a slice, as
defined in section 8.4.2.3 of the <<itu-t-h264,ITU-T H.264 Specification>>,
if any of the following conditions are true for the active
<<encode-h264-pps,PPS>> and the pname:pStdSliceHeader member of the
corresponding element of pname:pNaluSliceEntries:

  * pname:pStdSliceHeader->slice_type is code:STD_VIDEO_H264_SLICE_TYPE_P
    and code:weighted_pred_flag is enabled in the active PPS.
  * pname:pStdSliceHeader->slice_type is code:STD_VIDEO_H264_SLICE_TYPE_B
    and code:weighted_bipred_idc in the active PPS equals
    code:STD_VIDEO_H264_WEIGHTED_BIPRED_IDC_EXPLICIT.

.Valid Usage
****
  * [[VUID-VkVideoEncodeH264PictureInfoKHR-naluSliceEntryCount-08301]]
    pname:naluSliceEntryCount must: be between `1` and
    slink:VkVideoEncodeH264CapabilitiesKHR::pname:maxSliceCount, inclusive,
    as returned by flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the
    used video profile
  * [[VUID-VkVideoEncodeH264PictureInfoKHR-flags-08304]]
    If slink:VkVideoEncodeH264CapabilitiesKHR::pname:flags, as returned by
    flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used video
    profile, does not include
    ename:VK_VIDEO_ENCODE_H264_CAPABILITY_GENERATE_PREFIX_NALU_BIT_KHR, then
    pname:generatePrefixNalu must: be ename:VK_FALSE
  * [[VUID-VkVideoEncodeH264PictureInfoKHR-flags-08314]]
    If slink:VkVideoEncodeH264CapabilitiesKHR::pname:flags, as returned by
    flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used video
    profile, does not include
    ename:VK_VIDEO_ENCODE_H264_CAPABILITY_PREDICTION_WEIGHT_TABLE_GENERATED_BIT_KHR
    and the slice corresponding to any element of pname:pNaluSliceEntries
    uses <<encode-h264-weighted-pred,explicit weighted sample prediction>>,
    then
    slink:VkVideoEncodeH264NaluSliceInfoKHR::pname:pStdSliceHeader->pWeightTable
    must: not be `NULL` for that element of pname:pNaluSliceEntries
  * [[VUID-VkVideoEncodeH264PictureInfoKHR-flags-08315]]
    If slink:VkVideoEncodeH264CapabilitiesKHR::pname:flags, as returned by
    flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used video
    profile, does not include
    ename:VK_VIDEO_ENCODE_H264_CAPABILITY_DIFFERENT_SLICE_TYPE_BIT_KHR, then
    slink:VkVideoEncodeH264NaluSliceInfoKHR::pname:pStdSliceHeader->slice_type
    must: be identical for all elements of pname:pNaluSliceEntries
****

include::{generated}/validity/structs/VkVideoEncodeH264PictureInfoKHR.adoc[]
--

[open,refpage='VkVideoEncodeH264NaluSliceInfoKHR',desc='Structure specifies H.264 encode slice NALU parameters',type='structs']
--
The slink:VkVideoEncodeH264NaluSliceInfoKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264NaluSliceInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:constantQp is the QP to use for the slice if the current
    <<encode-rate-control-modes,rate control mode>> configured for the video
    session is ename:VK_VIDEO_ENCODE_RATE_CONTROL_MODE_DISABLED_BIT_KHR.
  * pname:pStdSliceHeader is a pointer to a
    code:StdVideoEncodeH264SliceHeader structure specifying
    <<encode-h264-slice-header-params,H.264 slice header parameters>> for
    the slice.

[[encode-h264-slice-header-params]]
Std Slice Header Parameters::

The members of the code:StdVideoEncodeH264SliceHeader structure pointed to
by pname:pStdSliceHeader are interpreted as follows:

  * code:flags.reserved and code:reserved1 are used only for padding
    purposes and are otherwise ignored;
  * if pname:pWeightTable is not `NULL`, then it is a pointer to a
    code:StdVideoEncodeH264WeightTable that is interpreted as follows:
  ** code:flags.reserved is used only for padding purposes and is otherwise
     ignored;
  ** all other members of code:StdVideoEncodeH264WeightTable are interpreted
     as defined in section 7.4.3.2 of the <<itu-t-h264,ITU-T H.264
     Specification>>;
  * all other members are interpreted as defined in section 7.4.3 of the
    <<itu-t-h264,ITU-T H.264 Specification>>.

include::{generated}/validity/structs/VkVideoEncodeH264NaluSliceInfoKHR.adoc[]
--

[open,refpage='VkVideoEncodeH264DpbSlotInfoKHR',desc='Structure specifies H.264 encode DPB picture information',type='structs']
--
The slink:VkVideoEncodeH264DpbSlotInfoKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264DpbSlotInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:pStdReferenceInfo is a pointer to a
    code:StdVideoEncodeH264ReferenceInfo structure specifying
    <<encode-h264-reference-info,H.264 reference information>>.

This structure is specified in the pname:pNext chain of
slink:VkVideoEncodeInfoKHR::pname:pSetupReferenceSlot, if not `NULL`, and
the pname:pNext chain of the elements of
slink:VkVideoEncodeInfoKHR::pname:pReferenceSlots to specify the
codec-specific reference picture information for an <<encode-h264,H.264
encode operation>>.

[[encode-h264-active-reference-picture-info]]
Active Reference Picture Information::

When this structure is specified in the pname:pNext chain of the elements of
slink:VkVideoEncodeInfoKHR::pname:pReferenceSlots, one element is added to
the list of <<encode-active-reference-picture-info,active reference
pictures>> used by the video encode operation for each element of
slink:VkVideoEncodeInfoKHR::pname:pReferenceSlots as follows:

  * The image subregion used is determined according to the
    <<encode-h264-picture-data-access,H.264 Encode Picture Data Access>>
    section.
  * The reference picture is associated with the <<dpb-slot,DPB slot>> index
    specified in the pname:slotIndex member of the corresponding element of
    slink:VkVideoEncodeInfoKHR::pname:pReferenceSlots.
  * The reference picture is associated with the
    <<encode-h264-reference-info,H.264 reference information>> provided in
    pname:pStdReferenceInfo.

[[encode-h264-reconstructed-picture-info]]
Reconstructed Picture Information::

When this structure is specified in the pname:pNext chain of
slink:VkVideoEncodeInfoKHR::pname:pSetupReferenceSlot, the information
related to the <<encode-reconstructed-picture-info,reconstructed picture>>
is defined as follows:

  * The image subregion used is determined according to the
    <<encode-h264-picture-data-access,H.264 Encode Picture Data Access>>
    section.
  * If <<encode-h264-ref-pic-setup,reference picture setup>> is requested,
    then the reconstructed picture is used to <<dpb-slot-states,activate>>
    the <<dpb-slot,DPB slot>> with the index specified in
    slink:VkVideoEncodeInfoKHR::pname:pSetupReferenceSlot->slotIndex.
  * The reconstructed picture is associated with the
    <<encode-h264-reference-info,H.264 reference information>> provided in
    pname:pStdReferenceInfo.

[[encode-h264-reference-info]]
Std Reference Information::

The members of the code:StdVideoEncodeH264ReferenceInfo structure pointed to
by pname:pStdReferenceInfo are interpreted as follows:

  * code:flags.reserved is used only for padding purposes and is otherwise
    ignored;
  * code: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-h264,ITU-T H.264 Specification>>;
  * code:primary_pic_type as defined in section 7.4.2 of the <<itu-t-h264,
    ITU-T H.264 Specification>>;
  * code:long_term_pic_num and code:long_term_frame_idx as defined in
    section 7.4.3 of the <<itu-t-h264,ITU-T H.264 Specification>>;
  * code:temporal_id as defined in section G.7.4.1.1 of the <<itu-t-h264,
    ITU-T H.264 Specification>>;
  * all other members are interpreted as defined in section 8.2 of the
    <<itu-t-h264,ITU-T H.264 Specification>>.

include::{generated}/validity/structs/VkVideoEncodeH264DpbSlotInfoKHR.adoc[]
--


[[encode-h264-rate-control]]
=== H.264 Encode Rate Control

[[encode-h264-gop]]
==== Group of Pictures

In case of H.264 encoding it is common practice to follow a regular pattern
of different picture types in display order when encoding subsequent frames.
This pattern is referred to as the _group of pictures_ (GOP).

[[encode-h264-regular-gop]]
A regular GOP is defined by the following parameters:

  * The number of frames in the GOP;
  * The number of consecutive B frames between I and/or P frames in display
    order.

GOPs are further classified as _open_ and _closed_ GOPs.

Frame types in an open GOP follow each other in display order according to
the following algorithm:

  1. The first frame is always an I frame.
  2. This is followed by a number of consecutive B frames, as defined above.
  3. If the number of frames in the GOP is not reached yet, then the next
     frame is a P frame and the algorithm continues from step 2.

[[encode-h264-open-gop]]
image::{images}/h26x_open_gop.svg[align="center",title="H.264 open GOP",opts="{imageopts}"]

[[encode-h264-idr-period]]
In case of a closed GOP, an <<encode-h264-idr-pic,IDR frame>> is used at a
certain period.

[[encode-h264-closed-gop]]
image::{images}/h26x_closed_gop.svg[align="center",title="H.264 closed GOP",opts="{imageopts}"]

It is also typical for H.264 encoding to use specific reference picture
usage patterns across the frames of the GOP.
The two most common reference patterns used are as follows:

[[encode-h264-ref-pattern-flat]]
Flat Reference Pattern::

  * Each P frame uses the last non-B frame, in display order, as reference.
  * Each B frame uses the last non-B frame, in display order, as its
    backward reference, and uses the next non-B frame, in display order, as
    its forward reference.

image::{images}/h26x_ref_pattern_flat.svg[align="center",title="H.264 flat reference pattern",opts="{imageopts}"]

[[encode-h264-ref-pattern-dyadic]]
Dyadic Reference Pattern::

  * Each P frame uses the last non-B frame, in display order, as reference.
  * The following algorithm is applied to the sequence of consecutive B
    frames between I and/or P frames in display order:

  . The B frame in the middle of this sequence uses the frame preceding the
    sequence as its backward reference, and uses the frame following the
    sequence as its forward reference.
  . The algorithm is executed recursively for the following frame sequences:
  ** The B frames of the original sequence preceding the frame in the
     middle, if any.
  ** The B frames of the original sequence following the frame in the
     middle, if any.

image::{images}/h26x_ref_pattern_dyadic.svg[align="center",title="H.264 dyadic reference pattern",opts="{imageopts}"]

The application can: provide guidance to the implementation's rate control
algorithm about the structure of the GOP used by the application.
Any such guidance about the GOP and its structure does not mandate that
specific GOP structure to be used by the application, as the picture type of
individual encoded pictures is still application-controlled, however, any
deviation from the provided guidance may: result in undesired rate control
behavior including, but not limited, to the implementation not being able to
conform to the expected average or target bitrates, or other rate control
parameters specified by the application.

When an H.264 encode session is used to encode multiple temporal layers, it
is also common practice to follow a regular pattern for the H.264 temporal
ID for the encoded pictures in display order when encoding subsequent
frames.
This pattern is referred to as the _temporal GOP_.
The most common temporal layer pattern used is as follows:

[[encode-h264-layer-pattern-dyadic]]
Dyadic Temporal Layer Pattern::

  * The number of frames in the temporal GOP is [eq]#2^n-1^#, where [eq]#n#
    is the number of temporal layers.
  * The [eq]#i#^th^ frame in the temporal GOP uses temporal ID [eq]#t#, if
    and only if the index of the least significant bit set in [eq]#i# equals
    [eq]#n-t-1#, except for the first frame, which is the only frame in the
    temporal GOP using temporal ID zero.
  * The [eq]#i#^th^ frame in the temporal GOP uses the [eq]#r#^th^ frame as
    reference, where [eq]#r# is calculated from [eq]#i# by clearing the
    least significant bit set in it, except for the first frame in the
    temporal GOP, which uses the first frame of the previous temporal GOP,
    if any, as reference.

image::{images}/h26x_layer_pattern_dyadic.svg[align="center",title="H.264 dyadic temporal layer pattern",opts="{imageopts}"]

[NOTE]
.Note
====
Multi-layer rate control and multi-layer coding are typically used for
streaming cases where low latency is expected, hence B pictures with forward
prediction are usually not used.
====

[open,refpage='VkVideoEncodeH264RateControlInfoKHR',desc='Structure describing H.264 stream rate control parameters',type='structs']
--
The sname:VkVideoEncodeH264RateControlInfoKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264RateControlInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:flags is a bitmask of
    elink:VkVideoEncodeH264RateControlFlagBitsKHR specifying H.264 rate
    control flags.
  * pname:gopFrameCount is the number of frames within a <<encode-h264-gop,
    group of pictures (GOP)>> intended to be used by the application.
    If it is set to 0, the rate control algorithm may: assume an
    implementation-dependent GOP length.
    If it is set to code:UINT32_MAX, the GOP length is treated as infinite.
  * pname:idrPeriod is the interval, in terms of number of frames, between
    two <<encode-h264-idr-pic,IDR frames>> (see <<encode-h264-idr-period,IDR
    period>>).
    If it is set to 0, the rate control algorithm may: assume an
    implementation-dependent IDR period.
    If it is set to code:UINT32_MAX, the IDR period is treated as infinite.
  * pname:consecutiveBFrameCount is the number of consecutive B frames
    between I and/or P frames within the <<encode-h264-gop,GOP>>.
  * pname:temporalLayerCount specifies the number of H.264 temporal layers
    that the application intends to use.

When an instance of this structure is included in the pname:pNext chain of
the slink:VkVideoCodingControlInfoKHR structure passed to the
flink:vkCmdControlVideoCodingKHR command, and
slink:VkVideoCodingControlInfoKHR::pname:flags includes
ename:VK_VIDEO_CODING_CONTROL_ENCODE_RATE_CONTROL_BIT_KHR, the parameters in
this structure are used as guidance for the implementation's rate control
algorithm (see <<video-coding-control,Video Coding Control>>).

If pname:flags includes
ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_ATTEMPT_HRD_COMPLIANCE_BIT_KHR, then
the rate control state is reset to an initial state to meet HRD compliance
requirements.
Otherwise the new rate control state may: be applied without a reset
depending on the implementation and the specified rate control parameters.

[NOTE]
.Note
====
It would be possible to infer the picture type to be used when encoding a
frame, on the basis of the values provided for pname:consecutiveBFrameCount,
pname:idrPeriod, and pname:gopFrameCount, but this inferred picture type
will not be used by implementations to override the picture type provided to
the video encode operation.
====

.Valid Usage
****
  * [[VUID-VkVideoEncodeH264RateControlInfoKHR-flags-08280]]
    If slink:VkVideoEncodeH264CapabilitiesKHR::pname:flags, as returned by
    flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used video
    profile, does not include
    ename:VK_VIDEO_ENCODE_H264_CAPABILITY_HRD_COMPLIANCE_BIT_KHR, then
    pname:flags must: not contain
    ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_ATTEMPT_HRD_COMPLIANCE_BIT_KHR
  * [[VUID-VkVideoEncodeH264RateControlInfoKHR-flags-08281]]
    If pname:flags contains
    ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REFERENCE_PATTERN_FLAT_BIT_KHR
    or
    ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REFERENCE_PATTERN_DYADIC_BIT_KHR,
    then it must: also contain
    ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REGULAR_GOP_BIT_KHR
  * [[VUID-VkVideoEncodeH264RateControlInfoKHR-flags-08282]]
    If pname:flags contains
    ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REFERENCE_PATTERN_FLAT_BIT_KHR,
    then it must: not also contain
    ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REFERENCE_PATTERN_DYADIC_BIT_KHR
  * [[VUID-VkVideoEncodeH264RateControlInfoKHR-flags-08283]]
    If pname:flags contains
    ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REGULAR_GOP_BIT_KHR, then
    pname:gopFrameCount must: be greater than `0`
  * [[VUID-VkVideoEncodeH264RateControlInfoKHR-idrPeriod-08284]]
    If pname:idrPeriod is not `0`, then it must: be greater than or equal to
    pname:gopFrameCount
  * [[VUID-VkVideoEncodeH264RateControlInfoKHR-consecutiveBFrameCount-08285]]
    If pname:consecutiveBFrameCount is not `0`, then it must: be less than
    pname:gopFrameCount
****

include::{generated}/validity/structs/VkVideoEncodeH264RateControlInfoKHR.adoc[]
--

[open,refpage='VkVideoEncodeH264RateControlFlagBitsKHR',desc='H.264 encode rate control bits',type='enums']
--
Bits which can: be set in
slink:VkVideoEncodeH264RateControlInfoKHR::pname:flags, specifying H.264
rate control flags, are:

include::{generated}/api/enums/VkVideoEncodeH264RateControlFlagBitsKHR.adoc[]

  * ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_ATTEMPT_HRD_COMPLIANCE_BIT_KHR
    specifies that rate control should: attempt to produce an HRD compliant
    bitstream, as defined in annex C of the <<itu-t-h264,ITU-T H.264
    Specification>>.
  * ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REGULAR_GOP_BIT_KHR specifies
    that the application intends to use a <<encode-h264-regular-gop, regular
    GOP structure>> according to the parameters specified in the
    pname:gopFrameCount, pname:idrPeriod, and pname:consecutiveBFrameCount
    members of the slink:VkVideoEncodeH264RateControlInfoKHR structure.
  * ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REFERENCE_PATTERN_FLAT_BIT_KHR
    specifies that the application intends to follow a
    <<encode-h264-ref-pattern-flat,flat reference pattern>> in the GOP.
  * ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_REFERENCE_PATTERN_DYADIC_BIT_KHR
    specifies that the application intends to follow a
    <<encode-h264-ref-pattern-dyadic,dyadic reference pattern>> in the GOP.
  * ename:VK_VIDEO_ENCODE_H264_RATE_CONTROL_TEMPORAL_LAYER_PATTERN_DYADIC_BIT_KHR
    specifies that the application intends to follow a
    <<encode-h264-layer-pattern-dyadic,dyadic temporal layer pattern>>.
--


[open,refpage='VkVideoEncodeH264RateControlFlagsKHR',desc='Bitmask specifying H.264 encode rate control flags',type='flags']
--
include::{generated}/api/flags/VkVideoEncodeH264RateControlFlagsKHR.adoc[]

tname:VkVideoEncodeH264RateControlFlagsKHR is a bitmask type for setting a
mask of zero or more elink:VkVideoEncodeH264RateControlFlagBitsKHR.
--


[[encode-h264-rate-control-layer]]
==== Rate Control Layers

[open,refpage='VkVideoEncodeH264RateControlLayerInfoKHR',desc='Structure describing H.264 per-layer rate control parameters',type='structs']
--
The sname:VkVideoEncodeH264RateControlLayerInfoKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264RateControlLayerInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:useMinQp indicates whether the QP values determined by rate
    control will be clamped to the lower bounds on the QP values specified
    in pname:minQp.
  * pname:minQp specifies the lower bounds on the QP values, for each
    picture type, that the implementation's rate control algorithm will use
    when pname:useMinQp is set to ename:VK_TRUE.
  * pname:useMaxQp indicates whether the QP values determined by rate
    control will be clamped to the upper bounds on the QP values specified
    in pname:maxQp.
  * pname:maxQp specifies the upper bounds on the QP values, for each
    picture type, that the implementation's rate control algorithm will use
    when pname:useMaxQp is set to ename:VK_TRUE.
  * pname:useMaxFrameSize indicates whether the implementation's rate
    control algorithm should: use the values specified in pname:maxFrameSize
    as the upper bounds on the encoded frame size for each picture type.
  * pname:maxFrameSize specifies the upper bounds on the encoded frame size,
    for each picture type, when pname:useMaxFrameSize is set to
    ename:VK_TRUE.

When used, the values in pname:minQp and pname:maxQp guarantee that the
effective QP values used by the implementation will respect those lower and
upper bounds, respectively.
However, limiting the range of QP values that the implementation is able to
use will also limit the capabilities of the implementation's rate control
algorithm to comply to other constraints.
In particular, the implementation may: not be able to comply to the
following:

  * The average and/or peak <<encode-bitrate,bitrate>> values to be used for
    the encoded bitstream specified in the pname:averageBitrate and
    pname:maxBitrate members of the
    slink:VkVideoEncodeRateControlLayerInfoKHR structure.
  * The upper bounds on the encoded frame size, for each picture type,
    specified in the pname:maxFrameSize member of
    sname:VkVideoEncodeH264RateControlLayerInfoKHR.

[NOTE]
.Note
====
In general, applications need to configure rate control parameters
appropriately in order to be able to get the desired rate control behavior,
as described in the <<encode-rate-control,Video Encode Rate Control>>
section.
====

When an instance of this structure is included in the pname:pNext chain of a
slink:VkVideoEncodeRateControlLayerInfoKHR structure specified in one of the
elements of the pname:pLayers array member of the
slink:VkVideoEncodeRateControlInfoKHR structure passed to the
flink:vkCmdControlVideoCodingKHR command,
slink:VkVideoCodingControlInfoKHR::pname:flags includes
ename:VK_VIDEO_CODING_CONTROL_ENCODE_RATE_CONTROL_BIT_KHR, and the bound
video session was created with the video codec operation
ename:VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR, it specifies the
H.264-specific rate control parameters of the rate control layer
corresponding to that element of pname:pLayers.

.Valid Usage
****
  * [[VUID-VkVideoEncodeH264RateControlLayerInfoKHR-useMinQp-08286]]
    If pname:useMinQp is ename:VK_TRUE, then the pname:qpI, pname:qpP, and
    pname:qpB members of pname:minQp must: all be between
    slink:VkVideoEncodeH264CapabilitiesKHR::pname:minQp and
    slink:VkVideoEncodeH264CapabilitiesKHR::pname:maxQp, as returned by
    flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used video profile
  * [[VUID-VkVideoEncodeH264RateControlLayerInfoKHR-useMaxQp-08287]]
    If pname:useMaxQp is ename:VK_TRUE, then the pname:qpI, pname:qpP, and
    pname:qpB members of pname:maxQp must: all be between
    slink:VkVideoEncodeH264CapabilitiesKHR::pname:minQp and
    slink:VkVideoEncodeH264CapabilitiesKHR::pname:maxQp, as returned by
    flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used video profile
  * [[VUID-VkVideoEncodeH264RateControlLayerInfoKHR-useMinQp-08288]]
    If pname:useMinQp is ename:VK_TRUE and
    slink:VkVideoEncodeH264CapabilitiesKHR::pname:flags, as returned by
    flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used video
    profile, does not include
    ename:VK_VIDEO_ENCODE_H264_CAPABILITY_PER_PICTURE_TYPE_MIN_MAX_QP_BIT_KHR,
    then the pname:qpI, pname:qpP, and pname:qpB members of pname:minQp
    must: all specify the same value
  * [[VUID-VkVideoEncodeH264RateControlLayerInfoKHR-useMaxQp-08289]]
    If pname:useMaxQp is ename:VK_TRUE and
    slink:VkVideoEncodeH264CapabilitiesKHR::pname:flags, as returned by
    flink:vkGetPhysicalDeviceVideoCapabilitiesKHR for the used video
    profile, does not include
    ename:VK_VIDEO_ENCODE_H264_CAPABILITY_PER_PICTURE_TYPE_MIN_MAX_QP_BIT_KHR,
    then the pname:qpI, pname:qpP, and pname:qpB members of pname:maxQp
    must: all specify the same value
  * [[VUID-VkVideoEncodeH264RateControlLayerInfoKHR-useMinQp-08374]]
    If pname:useMinQp and pname:useMaxQp are both ename:VK_TRUE, then the
    pname:qpI, pname:qpP, and pname:qpB members of pname:minQp must: all be
    less than or equal to the respective members of pname:maxQp
****

include::{generated}/validity/structs/VkVideoEncodeH264RateControlLayerInfoKHR.adoc[]
--

[open,refpage='VkVideoEncodeH264QpKHR',desc='Structure describing H.264 QP values per picture type',type='structs']
--
The sname:VkVideoEncodeH264QpKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264QpKHR.adoc[]

  * pname:qpI is the QP to be used for <<encode-h264-i-pic,I pictures>>.
  * pname:qpP is the QP to be used for <<encode-h264-p-pic,P pictures>>.
  * pname:qpB is the QP to be used for <<encode-h264-b-pic,B pictures>>.

include::{generated}/validity/structs/VkVideoEncodeH264QpKHR.adoc[]
--

[open,refpage='VkVideoEncodeH264FrameSizeKHR',desc='Structure describing frame size values per H.264 picture type',type='structs']
--
The sname:VkVideoEncodeH264FrameSizeKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264FrameSizeKHR.adoc[]

  * pname:frameISize is the size in bytes to be used for
    <<encode-h264-i-pic,I pictures>>.
  * pname:framePSize is the size in bytes to be used for
    <<encode-h264-p-pic,P pictures>>.
  * pname:frameBSize is the size in bytes to be used for
    <<encode-h264-b-pic,B pictures>>.

include::{generated}/validity/structs/VkVideoEncodeH264FrameSizeKHR.adoc[]
--


[[encode-h264-gop-remaining-frames]]
==== GOP Remaining Frames

Besides session level rate control configuration, the application can:
specify the number of frames per frame type remaining in the
<<encode-h264-gop,group of pictures (GOP)>>.

[open,refpage='VkVideoEncodeH264GopRemainingFrameInfoKHR',desc='Structure specifying H.264 encode rate control GOP remaining frame counts',type='structs']
--
The sname:VkVideoEncodeH264GopRemainingFrameInfoKHR structure is defined as:

include::{generated}/api/structs/VkVideoEncodeH264GopRemainingFrameInfoKHR.adoc[]

  * pname:sType is a elink:VkStructureType value identifying this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:useGopRemainingFrames indicates whether the implementation's rate
    control algorithm should: use the values specified in
    pname:gopRemainingI, pname:gopRemainingP, and pname:gopRemainingB.
    If pname:useGopRemainingFrames is ename:VK_FALSE, then the values of
    pname:gopRemainingI, pname:gopRemainingP, and pname:gopRemainingB are
    ignored.
  * pname:gopRemainingI specifies the number of <<encode-h264-i-pic,I
    frames>> the implementation's rate control algorithm should: assume to
    be remaining in the <<encode-h264-gop,GOP>> prior to executing the video
    encode operation.
  * pname:gopRemainingP specifies the number of <<encode-h264-p-pic,P
    frames>> the implementation's rate control algorithm should: assume to
    be remaining in the <<encode-h264-gop,GOP>> prior to executing the video
    encode operation.
  * pname:gopRemainingB specifies the number of <<encode-h264-b-pic,B
    frames>> the implementation's rate control algorithm should: assume to
    be remaining in the <<encode-h264-gop,GOP>> prior to executing the video
    encode operation.

Setting pname:useGopRemainingFrames to ename:VK_TRUE and including this
structure in the pname:pNext chain of slink:VkVideoBeginCodingInfoKHR is
only mandatory if the
slink:VkVideoEncodeH264CapabilitiesKHR::pname:requiresGopRemainingFrames
reported for the used <<video-profiles,video profile>> is ename:VK_TRUE.
However, implementations may: use these remaining frame counts, when
specified, even when it is not required.
In particular, when the application does not use a
<<encode-h264-regular-gop,regular GOP structure>>, these values may: provide
additional guidance for the implementation's rate control algorithm.

The slink:VkVideoEncodeH264CapabilitiesKHR::pname:prefersGopRemainingFrames
capability is also used to indicate that the implementation's rate control
algorithm may: operate more accurately if the application specifies the
remaining frame counts using this structure.

As with other rate control guidance values, if the effective order and
number of frames encoded by the application are not in line with the
remaining frame counts specified in this structure at any given point, then
the behavior of the implementation's rate control algorithm may: deviate
from the one expected by the application.

include::{generated}/validity/structs/VkVideoEncodeH264GopRemainingFrameInfoKHR.adoc[]
--


[[encode-h264-requirements]]
=== H.264 Encode Requirements

This section described the required: H.264 encoding capabilities for
physical devices that have at least one queue family that supports the video
codec operation ename:VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR, as
returned by flink:vkGetPhysicalDeviceQueueFamilyProperties2 in
slink:VkQueueFamilyVideoPropertiesKHR::pname:videoCodecOperations.

.Required <<video-std-header-version,Video Std Header Versions>>
[options="header"]
|====
| Video Std Header Name | Version
| `vulkan_video_codec_h264std_encode` | 1.0.0
|====

.Required Video Capabilities
[width="100%",cols="<35,<14,<11",options="header"]
|====
| Video Capability | Requirement | Requirement Type^1^
| **slink:VkVideoCapabilitiesKHR** | |
| pname:flags | - | min
| pname:minBitstreamBufferOffsetAlignment | 4096 | max
| pname:minBitstreamBufferSizeAlignment | 4096 | max
| pname:pictureAccessGranularity | (64,64) | max
| pname:minCodedExtent | - | max
| pname:maxCodedExtent | - | min
| pname:maxDpbSlots | 0 | min
| pname:maxActiveReferencePictures | 0 | min
| **slink:VkVideoEncodeCapabilitiesKHR** | |
| pname:flags | - | min
| pname:rateControlModes | - | min
| pname:maxBitrate | 64000 | min
| pname:maxQualityLevels | 1 | min
| pname:encodeInputPictureGranularity | (64,64) | max
| pname:supportedEncodeFeedbackFlags | ename:VK_VIDEO_ENCODE_FEEDBACK_BITSTREAM_BUFFER_OFFSET_BIT_KHR +
                                       ename:VK_VIDEO_ENCODE_FEEDBACK_BITSTREAM_BYTES_WRITTEN_BIT_KHR | min
| **slink:VkVideoEncodeH264CapabilitiesKHR** | |
| pname:flags | - | min
| pname:maxLevelIdc | code:STD_VIDEO_H264_LEVEL_IDC_1_0 | min
| pname:maxSliceCount | 1 | min
| pname:maxPPictureL0ReferenceCount | 0 | min
| pname:maxBPictureL0ReferenceCount | 0 | min
| pname:maxL1ReferenceCount | 0 | min
| pname:maxTemporalLayerCount | 1 | min
| pname:expectDyadicTemporalLayerPattern | - | implementation-dependent
| pname:minQp | - | max
| pname:maxQp | - | min
| pname:prefersGopRemainingFrames | - | implementation-dependent
| pname:requiresGopRemainingFrames | - | implementation-dependent
| pname:stdSyntaxFlags | - | min
|====

1::
    The *Requirement Type* column specifies the requirement is either the
    minimum value all implementations must: support, the maximum value all
    implementations must: support, or the exact value all implementations
    must: support.
    For bitmasks a minimum value is the least bits all implementations must:
    set, but they may: have additional bits set beyond this minimum.