Disclosed are a media stream conversion apparatus and a method for providing a multimedia service in a digital audio broadcasting (DAB) transmission system. First, multimedia data stream based on a moving picture experts group-2 (MPEG-2) system is analyzed to transmit multimedia data following the MPEG-2 system standard. Then, with use of the analyzed information, the multimedia data stream is reconstructed as an ensemble transport interface (ETI) frame in compliance with the ETI frame transport standard. The ETI frames are then converted into a DAB data stream, thereby providing a multimedia service in a DAB transmission system.