The invention relates to improving coding of media presentation description data. Requesting streamed timed media data associated with a media item, organized into temporal media segments, the streamed timed media data belonging to partitioned timed media data comprising timed samples, the streamed timed media data being transmitted as media segment files each comprising independently processed components resulting from processing the timed samples, including receiving a manifest comprising metadata for describing the processed components, the metadata comprising parameters used for describing a part of one of the processed components, wherein one of the parameters is a dynamic parameter which value can vary over time, the parameter being associated with an element referring to a metadata resource, external to the manifest and comprising a value defining the parameter; and requesting the streamed timed media data based on metadata of the manifest and of the value defining the parameter.