When composing several sources into a single output surface, we can specify the color of the background pixels using VAProcPipelineParameterBuffer::output_background_color. Currently this background color must be a 32-bit ARGB value.
But when the output is a non-RGB format, such as NV12, it would be helpful if we could set the background color to a constant YUV value instead. This would be very useful in scenarios where the composite surface is used as the input to another processing stage that expects YUV (e.g. video encoding).