A method of providing file data for a media file of a pre-determined format from a file system comprising a file record database and a data store, wherein the media file corresponds to a programme consisting of a plurality of segments, and wherein the segments included in the programme are dynamically determined. The method comprising the steps of receiving details of the programme including the duration of the programme, and determining the layout of the media file in the pre-determined format from the received details of the programme, the layout including locations for essence data within the file. A file record for the media file in the file record database is then created. In response to a request for the location of essence data within the file, a location given by determined layout of the media file is returned. Further, in response to an instruction that a segment is to be included in the programme, essence data corresponding to the contents of the segment is obtained. Then, in response to a request for a portion of essence data from the media file corresponding to a time period of the programme, essence data derived from the received essence data according to the determined layout of the media file is returned.