An apparatus for receiving a container file based on the International Standards Organization base media file format (ISOBMFF) comprising: means for receiving said container file, wherein the container file comprises media data and metadata, said media data and said metadata being enclosed in separate boxes, whereby said separate boxes comprise: at least two media data boxes (mdat) to enclose the media data, wherein each of the at least two media data boxes each contains media samples, and one movie box (moov) to enclose the metadata, said movie box (moov) including one or more track boxes (trak), wherein each track box (trak) encloses metadata related to the media data samples; and wherein at least one media data box is extended to comprise a media data box identifier value (mdat_identifier) identifying the at least one media data box from other media data boxes in the container file; and wherein at least one track box (trak) is associated with the at least one media data box (mdat) by comprising a data reference box (dref), wherein the data reference box (dref) comprises a data entry box (imdt) carrying: the media data box identifier value (mdat_identifier) as a data field, and an offset relative to the at least one media data box, pointing to the location of at least one media data sample in the at least one media data box; means for determining that the at least one media data sample is contained in the at least one media data box by checking the media data box identifier value (mdat_identifier) in the data entry box (imdt); and means for using the offset to obtain the at least one media data sample from the at least one media data box. means for receiving said container file, wherein the container file comprises media data and metadata, said media data and said metadata being enclosed in separate boxes, whereby said separate boxes comprise: at least two media data boxes (mdat) to enclose the media data, wherein each of the at least two media data boxes each contains media samples, and one movie box (moov) to enclose the metadata, said movie box (moov) including one or more track boxes (trak), wherein each track box (trak) encloses metadata related to the media data samples; and wherein at least one media data box is extended to comprise a media data box identifier value (mdat_identifier) identifying the at least one media data box from other media data boxes in the container file; and wherein at least one track box (trak) is associated with the at least one media data box (mdat) by comprising a data reference box (dref), wherein the data reference box (dref) comprises a data entry box (imdt) carrying: the media data box identifier value (mdat_identifier) as a data field, and an offset relative to the at least one media data box, pointing to the location of at least one media data sample in the at least one media data box; at least two media data boxes (mdat) to enclose the media data, wherein each of the at least two media data boxes each contains media samples, and one movie box (moov) to enclose the metadata, said movie box (moov) including one or more track boxes (trak), wherein each track box (trak) encloses metadata related to the media data samples; and wherein at least one media data box is extended to comprise a media data box identifier value (mdat_identifier) identifying the at least one media data box from other media data boxes in the container file; and wherein at least one track box (trak) is associated with the at least one media data box (mdat) by comprising a data reference box (dref), wherein the data reference box (dref) comprises a data entry box (imdt) carrying: the media data box identifier value (mdat_identifier) as a data field, and an offset relative to the at least one media data box, pointing to the location of at least one media data sample in the at least one media data box; wherein at least one media data box is extended to comprise a media data box identifier value (mdat_identifier) identifying the at least one media data box from other media data boxes in the container file; and wherein at least one track box (trak) is associated with the at least one media data box (mdat) by comprising a data reference box (dref), wherein the data reference box (dref) comprises a data entry box (imdt) carrying: the media data box identifier value (mdat_identifier) as a data field, and an offset relative to the at least one media data box, pointing to the location of at least one media data sample in the at least one media data box; the media data box identifier value (mdat_identifier) as a data field, and an offset relative to the at least one media data box, pointing to the location of at least one media data sample in the at least one media data box; means for determining that the at least one media data sample is contained in the at least one media data box by checking the media data box identifier value (mdat_identifier) in the data entry box (imdt); and means for using the offset to obtain the at least one media data sample from the at least one media data box.