1. A method of generating multimedia data, the method comprising: generating a scene tree by allocating at least one piece of first object information to each of a plurality of nodes and linking the nodes to one another based on the relationship between a plurality of pieces of second object information allocated to the nodes; adding a null node to which third object information of an exchangeable media object is allocated, to the scene tree; and recording the null node in a scene descriptor area in a scene description language.