DXVA (also known as DirectX VA) is the full name of the DirectX Video Acceleration (hardware video acceleration interface).
DXVA is a Microsoft and graphics chip manufacturers to the definition of a hardware interface specification. If a graphics chip to support DXVA hardware specifications, does not mean that it implements all the functions defined inside DXVA. However, one thing is certain: the definition for the DXVA functionality of each one, in line with DXVA specification graphics chip driver will tell the system to its hardware, this function is achieved or not achieved inside - this is a mandatory standard DXVA nature of requirements. The advantages of such an application does not have to spend time and effort to test the graphics card has a feature not implemented.
Similarly, if a decoder supports DXVA specification, it does not mean it can use all the features inside the DXVA specification combinations, it can choose its own ability to support, or want to support a combination of those features, while the other combination of functions perhaps to give up.
In addition, if a display driver chip, although the support by some kind of feature, but that the decoder chip, support for this feature is unstable, and easily lead to system crashes or error, then the decoder can also opt to use the chip, this kinds of functions.