Abstract: Media content (40) comprises content items (51), control data (55) which specifies branching points within the item at which presentation can be varied and conditional instructions to be used by the presentation device at the branching points and additional content segments (52, 53) to be used at the branching points. A media presentation device (10) presents the content item and uses the conditional instructions to vary presentation of the content item at a branching point. The media presentation device (10) maintains parameters which are used by the conditional instructions to vary presentation: a parameter of the environment external to the player; a parameter relating to operation of the player; a parameter relating to previous presentation of the content item; a parameter relating to a playlist comprising the content item; a preference of a user. Operations at a branching point include replacement, insertion, omission, repetition.