Get duration (in ms) of media descriptor object item.
    @param p_md: media descriptor object.
    @return: duration of media item or -1 on error.

def libvlc_media_get_duration(p_md):
    '''Get duration (in ms) of media descriptor object item.
    @param p_md: media descriptor object.
    @return: duration of media item or -1 on error.
    '''
    f = _Cfunctions.get('libvlc_media_get_duration', None) or \
        _Cfunction('libvlc_media_get_duration', ((1,),), None,
                    ctypes.c_longlong, Media)
    return f(p_md)