marked the same as both of its fields. A picture that is marked as "used for short-term reference" is identified by its FrameNum and, when it is a field, by its parity. A picture that is marked as "used for long-term reference" is identified by its LongTermFrameIdx and, when it is a field, by its parity. Frames or complementary field pairs marked as "used for short-term reference" or as "used for long-term reference" can be used as a reference for inter prediction when decoding a frame until the frame, the complementary field pair, or one of its constituent fields is marked as "unused for reference". A field marked as "used for short-term reference" or as "used for long-term reference" can be used as a reference for inter prediction when decoding a field until marked as "unused for reference". NOTE 2 - The marking status of a frame or complementary field pair can always be deduced from the marking status of its two fields. If both fields of a frame or complementary field pair are marked as "used for reference", the frame or complementary field pair is also marked as "used for reference"; otherwise (one field or both fields of a frame or complementary field pair are marked as "unused for reference"), the frame or complementary field pair is marked as "unused for reference". A picture can be marked as "unused for reference" by the sliding window reference picture marking process, a first-in, first-out mechanism specified in clause 8.2.5.3 or by the adaptive memory control reference picture marking process, a customised adaptive marking operation specified in clause 8.2.5.4. A short-term reference picture is identified for use in the decoding process by its variables FrameNum and FrameNumWrap and its picture number PicNum, and a long-term reference picture is identified for use in the decoding process by its long-term picture number LongTermPicNum. When the current picture is not an IDR picture, clause 8.2.4.1 is invoked to specify the assignment of the variables FrameNum, FrameNumWrap, PicNum and LongTermPicNum. Re