In a video/audio coding and multiplexing method, coding of multimedia data including video data and audio data is implemented as a software program operating on a multitask operating system, and video/audio coded and multiplexed information in which video/audio synchronization is realized in specified time units is obtained. In this method, coded video information and coded audio information are temporarily stored in a video buffer and an audio buffer, respectively. A video/audio synchronization means creates time and information using video block rate information which is created on the basis of the coded video information and stored with the coded video information. According to the time information, a coded video read-out means and a coded audio read-out means read the coded video information and the coded audio information from the respective buffers, and the video/audio synchronization means performs video/audio multiplexing. Thereby, the coding process and the multiplexing process are performed at independent timings.