Multiplex transmission method and system, and audio jitter absorbing method used therein

A multiplex frame is of a fixed length and includes a header and a fixed-length field. The fixed-length field is divided into variable-length slots 1 and 2. The length of the variable-length slot 1 is a predetermined fixed length when data to be stored exists and is zero with no data to be stored. The length of the variable-length slot 2 is increased/decreased depending on the length of the variable-length slot 1. Fixed-length data not employing retransmission (e.g., an audio frame) is transmitted in the first variable-length slot and one complete variable-length data employing retransmission (e.g., a data link frame of video) is transmitted in the second variable-length slot. When the multiplex frame thus has a fixed length and the frame length of the data link frame of the variable-length data employing retransmission is changed depending on the length of the fixed-length data not employing retransmission, the transmitting timing of the data link frames can be fixed with respect to the transmission stream of the multiplex frames. Then the boundaries between the data link frames are not lost due to a transmission error, which improves the error robustness. That is to say, even if the slot synchronization is lost due to a transmission error, it is possible to see the next header at once, providing easy resynchronization.