C Specification

When calling vkGetPhysicalDeviceVideoCapabilitiesKHR with pVideoProfile->videoCodecOperation specifying an encode operation, the VkVideoEncodeCapabilitiesKHR structure must be included in the pNext chain of the VkVideoCapabilitiesKHR structure to retrieve capabilities specific to video encoding.

The VkVideoEncodeCapabilitiesKHR structure is defined as:

// Provided by VK_KHR_video_encode_queue
typedef struct VkVideoEncodeCapabilitiesKHR {
    VkStructureType                         sType;
    void*                                   pNext;
    VkVideoEncodeCapabilityFlagsKHR         flags;
    VkVideoEncodeRateControlModeFlagsKHR    rateControlModes;
    uint32_t                                maxRateControlLayers;
    uint64_t                                maxBitrate;
    uint32_t                                maxQualityLevels;
    VkExtent2D                              encodeInputPictureGranularity;
    VkVideoEncodeFeedbackFlagsKHR           supportedEncodeFeedbackFlags;
} VkVideoEncodeCapabilitiesKHR;

Members

  • sType is a VkStructureType value identifying this structure.

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

  • flags is a bitmask of VkVideoEncodeCapabilityFlagBitsKHR describing supported encoding features.

  • rateControlModes is a bitmask of VkVideoEncodeRateControlModeFlagBitsKHR indicating supported rate control modes.

  • maxRateControlLayers indicates the maximum number of rate control layers supported.

  • maxBitrate indicates the maximum supported bitrate.

  • maxQualityLevels indicates the number of discrete video encode quality levels supported. Implementations must support at least one quality level.

  • encodeInputPictureGranularity indicates the granularity at which encode input picture data is encoded and may indicate a texel granularity up to the size of the codec-specific coding block size. This capability does not impose any valid usage constraints on the application, however, depending on the contents of the encode input picture, it may have effects on the encoded bitstream, as described in more detail below.

  • supportedEncodeFeedbackFlags is a bitmask of VkVideoEncodeFeedbackFlagBitsKHR values specifying the supported flags for video encode feedback queries.

Description

Implementations must include support for at least VK_VIDEO_ENCODE_FEEDBACK_BITSTREAM_BUFFER_OFFSET_BIT_KHR and VK_VIDEO_ENCODE_FEEDBACK_BITSTREAM_BYTES_WRITTEN_BIT_KHR in supportedEncodeFeedbackFlags.

encodeInputPictureGranularity provides information about the way encode input picture data is used as input to video encode operations. In particular, some implementations may not be able to limit the set of texels used to encode the output video bitstream to the image subregion specified in the VkVideoPictureResourceInfoKHR structure corresponding to the encode input picture (i.e. to the resolution of the image data to encode specified in its codedExtent member).

Note

For example, the application requests the coded extent to be 1920x1080, but the implementation is only able to source the encode input picture data at the granularity of the codec-specific coding block size which is 16x16 pixels (or as otherwise indicated in encodeInputPictureGranularity). In this example, the content is horizontally aligned with the coding block size, but not vertically aligned with it. Thus encoding of the last row of coding blocks will be impacted by the contents of the input image at texel rows 1080 to 1087 (the latter being the next row which is vertically aligned with the coding block size, assuming a zero-based texel row index).

If codedExtent rounded up to the next integer multiple of encodeInputPictureGranularity is greater than the extent of the image subresource specified for the encode input picture, then the texel values corresponding to texel coordinates outside of the bounds of the image subresource may be undefined. However, implementations should use well-defined default values for such texels in order to maximize the encoding efficiency for the last coding block row/column, and/or to ensure consistent encoding results across repeated encoding of the same input content. Nonetheless, the values used for such texels must not have an effect on whether the video encode operation produces a compliant bitstream, and must not have any other effects on the encoded picture data beyond what may otherwise result from using these texel values as input to any compression algorithm, as defined in the used video compression standard.

Note

While not required, it is generally a good practice for applications to make sure that the image subresource used for the encode input picture has an extent that is an integer multiple of the codec-specific coding block size (or at least encodeInputPictureGranularity) and that this padding area is filled with known values in order to improve encoding efficiency, portability, and reproducibility.
Valid Usage (Implicit)

  • VUID-VkVideoEncodeCapabilitiesKHR-sType-sType
    sType must be VK_STRUCTURE_TYPE_VIDEO_ENCODE_CAPABILITIES_KHR

See Also

VK_KHR_video_encode_queue, VkExtent2D, VkStructureType, VkVideoEncodeCapabilityFlagsKHR, VkVideoEncodeFeedbackFlagsKHR, VkVideoEncodeRateControlModeFlagsKHR

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 2014-2024 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0