VkVideoEncodeRateControlInfoKHR

The VkVideoEncodeRateControlInfoKHR structure is defined as:

typedef struct VkVideoEncodeRateControlInfoKHR {
    VkStructureType sType;
    const void* pNext;
    VkVideoEncodeRateControlFlagsKHR flags;
    VkVideoEncodeRateControlModeFlagBitsKHR rateControlMode;
    uint32_t layerCount;
    const VkVideoEncodeRateControlLayerInfoKHR* pLayers;
    uint32_t virtualBufferSizeInMs;
    uint32_t initialVirtualBufferSizeInMs;
} VkVideoEncodeRateControlInfoKHR;

• sType is a VkStructureType value identifying this structure.
• pNext is NULL or a pointer to a structure extending this structure.
• flags is reserved for future use.
• rateControlMode is a VkVideoEncodeRateControlModeFlagBitsKHR value specifying the rate control mode.
• layerCount specifies the number of rate control layers to use.
• pLayers is a pointer to an array of layerCount
  VkVideoEncodeRateControlLayerInfoKHR structures, each specifying the rate control configuration of the corresponding rate control layer.
• virtualBufferSizeInMs is the size in milliseconds of the virtual buffer used by the implementation’s rate control algorithm for the leaky bucket model, with respect to the average bitrate of the stream calculated by summing the values of the averageBitrate members of the elements of the pLayers array.
• initialVirtualBufferSizeInMs is the initial occupancy in milliseconds of the virtual buffer used by the implementation’s rate control algorithm for the leaky bucket model.

If layerCount is zero then the values of virtualBufferSizeInMs and initialVirtualBufferSizeInMs are ignored.

This structure can be specified in the following places:

• In the pNext chain of VkVideoBeginCodingInfoKHR to specify the current rate control state expected to be configured when beginning a video coding scope.
• In the pNext chain of VkVideoCodingControlInfoKHR to change the rate control configuration of the bound video session.

Including this structure in the pNext chain of VkVideoCodingControlInfoKHR and including VK_VIDEO_CODING_CONTROL_ENCODE_RATE_CONTROL_BIT_KHR in VkVideoCodingControlInfoKHR::flags enables updating the rate control configuration of the bound video session. This replaces the entire rate control configuration of the bound video session and may reset the state of all enabled rate control layers to an initial state according to the codec-specific rate control semantics defined in the corresponding sections listed below.

When layerCount is greater than one, multiple rate control layers are configured, and each rate control layer is applied to the corresponding video coding layer identified by the index of the corresponding element of pLayer.

• If the video session was created with the video codec operation VK_VIDEO_CODEC_OPERATION_ENCODE_H264_BIT_KHR, then this index specifies the H.264 temporal layer ID of the video coding layer the rate control layer is applied to.
• If the video session was created with the video codec operation VK_VIDEO_CODEC_OPERATION_ENCODE_H265_BIT_KHR, then this index specifies the H.265 temporal ID of the video coding layer the rate control layer is applied to.

Additional structures providing codec-specific rate control parameters can be included in the pNext chain of VkVideoCodingControlInfoKHR depending on the video profile the bound video session was created. For further details see:

• Video Coding Control
• H.264 Encode Rate Control
• H.265 Encode Rate Control

The new rate control configuration takes effect when the corresponding vkCmdControlVideoCodingKHR is executed on the device, and only impacts video encode operations that follow in execution order.