CODECAPI_AVEncVideoInputDeltaQPBlockSettings property

Read-only property that specifies the settings that the encoder MFT supports for delta QP input values.

Data type

InputQPSettings (VT_BLOB)

Property GUID

CODECAPI_AVEncVideoInputDeltaQPBlockSettings

Property value

The value of this property is an InputQPSettings structure. If the property is present, the video encoder MFT supports receiving delta (relative) QP values that conform to the settings provided by the InputQPSettings structure. If the property is missing, the video encoder MFT does not support receiving delta QP values.

When supported, delta QP values can be provided as input for the video encoder MFT to apply during the quantization step of the encoding process. The MFSampleExtension_VideoEncodeInputDeltaQPMap attribute is used to provide the delta QP values.

Remarks

Each element in the QP map represents a square block of pixels, with a side of N pixels, making the total number of pixels contained within such a block N2 (NxN). The block size is specified as the number of pixels on one side of the square block (i.e., the value N.) The size of such blocks maps to Luma pixels.

Use ICodecAPI::IsSupported to check if the encoder supports receiving delta QP values.

Use ICodecAPI::GetValue to obtain the values represented within the InputQPSettings struct using the VT_BLOB interface. This is a ready-only property and therefore calling ICodecAPI::SetValue will have no effect.

The minBlockSize and maxBlockSize fields of the InputQPSettings structure may have the same value, indicating that the encoder only supports a single block size.

Rectangular blocks of size MxN (e.g., 32x16), are not supported.

Providing delta QP values may conflict and have an overriding effect on bitrate properties like AVEncCommonMeanBitRate or CODECAPI_AVEncCommonMaxBitRate.

Examples

The following example demonstrates how to use the CODECAPI_AVEncVideoInputDeltaQPSettings property to check if an encoder MFT supports receiving delta QP maps. The function prints the minimum and maximum supported block sizes, and the stepping delta. This information can be used by the app to choose an appropriate block size for the delta QP map.

#include <codecapi.h>
#include <mfapi.h>
#include <stdio.h>
#include <wil/resource.h>
#include <wil/result_macros.h>

//  This function assumes that the encoder MFT supports ICodecAPI interface.
//  It checks if CODECAPI_AVEncVideoInputDeltaQPBlockSettings is supported & prints the block size details
HRESULT PrintEncoderDeltaQPMapBlockSize(In IMFTransform* encoder)
{
    wil::com_ptr_nothrow<ICodecAPI> codecAPI;
    RETURN_IF_FAILED(wil::com_query_to_nothrow(encoder, &codecAPI));

    // Check if the encoder supports receiving delta QP maps.
    if (!codecAPI->IsSupported(&CODECAPI_AVEncVideoInputDeltaQPBlockSettings))
    {
        printf("The encoder does not support receiving delta QP maps.\n");
        return S_OK;
    }

    // Retrieve the InputQPSettings blob via GetValue (VT_BLOB).
    wil::unique_variant var;
    RETURN_IF_FAILED(codecAPI->GetValue(&CODECAPI_AVEncVideoInputDeltaQPBlockSettings, &var));
    RETURN_HR_IF(E_UNEXPECTED, var.vt != VT_BLOB || var.blob.cbSize < sizeof(InputQPSettings));

    // Cast blob data to InputQPSettings
    const InputQPSettings* settings = reinterpret_cast<const InputQPSettings*>(var.blob.pBlobData);
    printf("Min Delta QP Block Size  = %u\n", settings->minBlockSize);
    printf("Max Delta QP Block Size  = %u\n", settings->maxBlockSize);
    printf("Step Delta QP Block Size = %u\n", settings->stepsBlockSize);
    return S_OK;
}

Requirements

See also

• Media Foundation Properties
• ICodecAPI