Systems, methods and apparatus for processing visual media data are described. One example method includes performing a conversion between visual media data and a visual media file that includes one or more tracks that store one or more bitstreams of the visual media data; and wherein the visual media data comprises one or more pictures comprising one or more subpictures or one or more slices; wherein the visual media file stores the one or more tracks according to a format rule; and wherein the format rule specifies that a track that includes a sequence of the one or more slices or the one or more subpictures covers a rectangular area of the one or more pictures.