Apparatus and method for interfacing between A/V system and portable device

An interface apparatus and method for transmission and reception of a control signal and a digital stream between an audio/video (A/V) system and a digital data recording and/or reproducing device are provided. The device for recording and/or reproducing digital data includes: a storage unit storing digital data encoded in a predetermined format; a decoder unit decoding digital data stored in the storage unit; an interface unit transmitting the decoded data to an external device; and a control unit controlling the storage unit, the decoder unit, and the interface unit.