Function vaCreateContext 

pub unsafe extern "C" fn vaCreateContext(
    dpy: VADisplay,
    config_id: VAConfigID,
    picture_width: c_int,
    picture_height: c_int,
    flag: c_int,
    render_targets: *mut VASurfaceID,
    num_render_targets: c_int,
    context: *mut VAContextID,
) -> VAStatus

vaCreateContext - Create a context dpy: display config_id: configuration for the context picture_width: coded picture width picture_height: coded picture height flag: any combination of the following: VA_PROGRESSIVE (only progressive frame pictures in the sequence when set) render_targets: a hint for render targets (surfaces) tied to the context num_render_targets: number of render targets in the above array context: created context id upon return