1. A method of providing supplemental information to be reproduced with audio/video data, the method comprising: receiving a broadcast signal through an antenna; obtaining audio/video data from the broadcast signal and supplemental information associated with the audio/video data, wherein the supplemental information comprises segment units, wherein the supplemental information is provided separately from the audio/video data by identification information, and wherein the supplemental information is linked to the audio/video data by linking information; decoding the supplemental information and the audio/video data; and outputting the supplemental information synchronously with the audio/video data.