because RenderProcessor (dxva) method uses (0,0,m_sourceWidth,m_sourceHeight) as destination rectangle to render into m_IntermediateTarget (if used HQ scalers) ie renders the video as is https://github.com/afedchin/xbmc/blob/09ff304601d34a88a314e30139eaa42020ec5bb0/xbmc/cores/VideoRenderers/WinRenderer.cpp#L946