A method of content sub-item substitution is described. The method includes: receiving from a headend a description of a plurality of virtual channels, the description defining each virtual channel on the basis of one or more metadata attributes associated with that virtual channel; receiving one or more content sub-item substitution opportunities for each virtual channel, each content sub-item substitution opportunity specifying one or more content sub-items for use in the content sub-item substitution; and receiving and recording a content item, the content item including metadata associated with the content item and one or more substitutable content sub-items. The method further includes, upon playback (201) of a previously recorded content item: matching the metadata associated with the previously recorded content item with the one or more metadata attributes, thereby determining a virtual channel (205) valid for the previously recorded content item; selecting a content sub-item substitution opportunity (207) based on the determined virtual channel; and substituting the one or more substitutable content sub-items (211) with content sub-items specified in the selected content sub-item substitution opportunity. Related apparatus and methods are also disclosed.