Function vaDeriveImage 

pub unsafe extern "C" fn vaDeriveImage(
    dpy: VADisplay,
    surface: VASurfaceID,
    image: *mut VAImage,
) -> VAStatus

Derive an VAImage from an existing surface. This interface will derive a VAImage and corresponding image buffer from an existing VA Surface. The image buffer can then be mapped/unmapped for direct CPU access. This operation is only possible on implementations with direct rendering capabilities and internal surface formats that can be represented with a VAImage. When the operation is not possible this interface will return VA_STATUS_ERROR_OPERATION_FAILED. Clients should then fall back to using vaCreateImage + vaPutImage to accomplish the same task in an indirect manner.

Implementations should only return success when the resulting image buffer would be useable with vaMap/Unmap.

When directly accessing a surface special care must be taken to insure proper synchronization with the graphics hardware. Clients should call vaQuerySurfaceStatus to insure that a surface is not the target of concurrent rendering or currently being displayed by an overlay.

Additionally nothing about the contents of a surface should be assumed following a vaPutSurface. Implementations are free to modify the surface for scaling or subpicture blending within a call to vaPutImage.

Calls to vaPutImage or vaGetImage using the same surface from which the image has been derived will return VA_STATUS_ERROR_SURFACE_BUSY. vaPutImage or vaGetImage with other surfaces is supported.

An image created with vaDeriveImage should be freed with vaDestroyImage. The image and image buffer structures will be destroyed; however, the underlying surface will remain unchanged until freed with vaDestroySurfaces.