The audio mixing algorithm determines the quality of the mixing voice in the unicast based centralized multimedia conference system. However

the implementation of the mixing algorithm is based on the backup of synchronous audio mixing and transmitting mechanism. The circular mixing buffer (CMB) proposed by Perkins is analyzed

and then a realtime synchronous audio mixing and transmitting scheme is presented. This scheme is achieved by setting multiCMBs and controlling them synchronously. The length of data used for mixing is decided by the one of data storing in the soundcard buffer which reflects operating system (OS) scheduling. This can alleviate the influence of OS scheduling on the audio mixing operation. Experiment results manifest that our scheme is feasible and steady.