A method of generating an audio signal for an audiovisual content item, the method comprising: receiving an audiovisual content item data stream comprising a plurality of individual audiovisual data streams, the plurality of individual audiovisual data streams comprising audiovisual components for an audiovisual content item; each audiovisual data stream comprising encoded data representing at least one audiovisual component and synchronization data; wherein the audiovisual content item data stream comprises a first individual audiovisual data stream comprising first audio data for an audio representation for the audiovisual content item, the first audio data comprising mandatory audio data for the audio representation and replaceable audio data for the audio representation, the mandatory audio data corresponding to an audio component that must be rendered when the audio representation is rendered and the replaceable audio data corresponding to a replaceable audio component that can be substituted by an alternative audio component when the audio representation is rendered, the audiovisual content item data stream further comprising a content item map table for the audiovisual content item, the content item map table comprising a list of audiovisual data stream packet identifiers for data packets for audiovisual data streams linked to the audiovisual content item, and the content item map table comprising a common data stream packet identifier for the audiovisual content item for a set of at least two of the plurality of individual audiovisual data streams; the method further comprising: extracting the mandatory audio data from the first audio data in response to the common data stream packet identifier; retrieving alternative audio data; replacing the replaceable audio data by the alternative audio data; and generating the audio signal from the mandatory audio data and the alternative audio data. receiving an audiovisual content item data stream comprising a plurality of individual audiovisual data streams, the plurality of individual audiovisual data streams comprising audiovisual components for an audiovisual content item; each audiovisual data stream comprising encoded data representing at least one audiovisual component and synchronization data; wherein the audiovisual content item data stream comprises a first individual audiovisual data stream comprising first audio data for an audio representation for the audiovisual content item, the first audio data comprising mandatory audio data for the audio representation and replaceable audio data for the audio representation, the mandatory audio data corresponding to an audio component that must be rendered when the audio representation is rendered and the replaceable audio data corresponding to a replaceable audio component that can be substituted by an alternative audio component when the audio representation is rendered, the audiovisual content item data stream further comprising a content item map table for the audiovisual content item, the content item map table comprising a list of audiovisual data stream packet identifiers for data packets for audiovisual data streams linked to the audiovisual content item, and the content item map table comprising a common data stream packet identifier for the audiovisual content item for a set of at least two of the plurality of individual audiovisual data streams; the method further comprising: extracting the mandatory audio data from the first audio data in response to the common data stream packet identifier; retrieving alternative audio data; replacing the replaceable audio data by the alternative audio data; and generating the audio signal from the mandatory audio data and the alternative audio data. extracting the mandatory audio data from the first audio data in response to the common data stream packet identifier; retrieving alternative audio data; replacing the replaceable audio data by the alternative audio data; and generating the audio signal from the mandatory audio data and the alternative audio data.