A method for generating additional information for guaranteeing seamless playback of data streams includes generating data stream information for each of two or more data streams, which includes packet data to which information on an arrival time of the respective packet data is added. The data stream information includes seamless playback information, which indicates whether a corresponding data stream is to be seamlessly reproduced after playback of a preceding data stream, and/or seamless time control information for controlling an output time of the corresponding data stream to be seamlessly reproduced. Therefore, data streams can be seamlessly reproduced without interruption between the data streams, by using data stream information which includes seamless information and/or seamless time control information including reference time, an offset value and/or a gap length value. Additionally, even if data streams are edited, the data streams can be seamlessly reproduced by just modifying data stream information.