ID3D11VideoContext::VideoProcessorSetStreamAlpha method

Sets the planar alpha for an input stream on the video processor.


void VideoProcessorSetStreamAlpha(
  [in] ID3D11VideoProcessor *pVideoProcessor,
  [in] UINT                 StreamIndex,
  [in] BOOL                 Enable,
  [in] FLOAT                Alpha


pVideoProcessor [in]

A pointer to the ID3D11VideoProcessor interface. To get this pointer, call ID3D11VideoDevice::CreateVideoProcessor.

StreamIndex [in]

The zero-based index of the input stream. To get the maximum number of streams, call ID3D11VideoProcessorEnumerator::GetVideoProcessorCaps and check the MaxStreamStates structure member.

Enable [in]

Specifies whether alpha blending is enabled.

Alpha [in]

The planar alpha value. The value can range from 0.0 (transparent) to 1.0 (opaque). If Enable is FALSE, this parameter is ignored.

Return value

This method does not return a value.


To use this feature, the driver must support stereo video, indicated by the D3D11_VIDEO_PROCESSOR_FEATURE_CAPS_ALHPA_STREAM capability flag. To query for this capability, call ID3D11VideoProcessorEnumerator::GetVideoProcessorCaps.

Alpha blending is disabled by default.

For each pixel, the destination color value is computed as follows:

Cd = Cs * (As * Ap * Ae) + Cd * (1.0 - As * Ap * Ae)


  • Cd = The color value of the destination pixel
  • Cs = The color value of the source pixel
  • As = The per-pixel source alpha
  • Ap = The planar alpha value
  • Ae = The palette-entry alpha value, or 1.0 (see Note)
Note  Palette-entry alpha values apply only to palettized color formats, and only when the device supports the D3D11_VIDEO_PROCESSOR_FEATURE_CAPS_ALPHA_PALETTE capability. Otherwise, this factor equals 1.0.

The destination alpha value is computed according to the alpha fill mode. For more information, see ID3D11VideoContext::VideoProcessorSetOutputAlphaFillMode.


Minimum supported client

Windows 8 [desktop apps | UWP apps]

Minimum supported server

Windows Server 2012 [desktop apps | UWP apps]

Minimum supported phone

Windows Phone 8



See also