A data transmission method for MPEG Media Transport, MMT, said method comprising: generating a plurality of Media Processing Units, MPUs, each of which being composed of a plurality of samples, and reference clock time information indicating a reference clock time for setting a current clock time; and transmitting the generated plurality of MPUs and the generated reference clock time information; periodically performing a step of generating and transmitting leading clock time information which includes, for each of a plurality of specific MPUs, a Presentation Time Stamp, PTS, or a Decoding Time Stamp, DTS, indicating a clock time point at which a leading sample in the specific MPU is to be presented or decoded, the plurality of specific MPUs being MPUs of the plurality of MPUs that are to be presented or decoded after the leading clock time information is transmitted, and calculating a final reception clock time (T_last) by adding a propagation time necessary for a data playback device to receive data since the data is transmitted (Trans_time) and a maximum value of the delay time until the reception of the specific MPUs is started since the data playback device receives the leading clock time information (Max_delay) and the clock time at which the leading clock time information is transmitted (T_send), wherein the leading clock time information indicates the leading clock times of all the MPUs in which the leading sample is to be presented or decoded after the clock time at which the leading clock time information is transmitted (T_send) and at or before the smaller one of the final reception clock time (T_last) and the transmission clock time of the next leading clock time information (T_send+T), wherein the plurality of MPUs and the leading clock time information are transmitted in separate transmission packets or units, each of the generated plurality of MPUs indicates a time point at which each sample except for the leading sample in the MPU is presented or decoded, as a relative value to a time point of another sample in the MPU. generating a plurality of Media Processing Units, MPUs, each of which being composed of a plurality of samples, and reference clock time information indicating a reference clock time for setting a current clock time; and transmitting the generated plurality of MPUs and the generated reference clock time information; periodically performing a step of generating and transmitting leading clock time information which includes, for each of a plurality of specific MPUs, a Presentation Time Stamp, PTS, or a Decoding Time Stamp, DTS, indicating a clock time point at which a leading sample in the specific MPU is to be presented or decoded, the plurality of specific MPUs being MPUs of the plurality of MPUs that are to be presented or decoded after the leading clock time information is transmitted, and calculating a final reception clock time (T_last) by adding a propagation time necessary for a data playback device to receive data since the data is transmitted (Trans_time) and a maximum value of the delay time until the reception of the specific MPUs is started since the data playback device receives the leading clock time information (Max_delay) and the clock time at which the leading clock time information is transmitted (T_send), wherein the leading clock time information indicates the leading clock times of all the MPUs in which the leading sample is to be presented or decoded after the clock time at which the leading clock time information is transmitted (T_send) and at or before the smaller one of the final reception clock time (T_last) and the transmission clock time of the next leading clock time information (T_send+T), wherein the plurality of MPUs and the leading clock time information are transmitted in separate transmission packets or units, each of the generated plurality of MPUs indicates a time point at which each sample except for the leading sample in the MPU is presented or decoded, as a relative value to a time point of another sample in the MPU.