An apparatus and method are provided for securing service quality in multimedia services. The method includes arranging media data samples in each data frame (moof) included a data field of a media data box (mdat), according to a specific rule, and recording control information based on the specific rule in a control information field (sidx) of the mdat. The control information defines an arrangement of the samples in each moof, and includes level information about a level assigned to each sample and index information about a location where each sample is arranged in the data field.