A DVD playback system, associated with a DVD storage media. The graft material includes clot material preferably derived from non-anticoagulated bone marrow aspirate, which significantly improves the efficacy of the graft. The tensioner is rendered operative after the pivot structure is uncoupled from the adjusting member, thus allowing the pivot structure to pivot with respect to the adjusting member. When a failure arises in the first and second turning control systems or after the turning characteristic is changed, the electromagnetic clutch is brought into a connected state, whereby the steering apparatus is switched to a steer-by-mechanical connection mode. The fixing seat comprises a fixing post axially defining a through hole; the fiber ferrule is aligned to the fixing post. By utilizing two switching units to improve the latching speed of the latching unit of the level shifter, the duty cycle of the input signal is nearly equal to the duty cycle of the output signal.