In this paper, QOS Control of realtime multimedia communication system under heterogeneous environment by the wired and the wireless networks is proposed. In our suggested system, as channel coding, FEC (Forward Error Correction) method with Reed-Solomon coding is introduced to reduce the packet error rate on the wireless network. On the other hand, as source coding, transcoding methods including transformation of various video codings such as M-JPEG, MPEG and Quicktime, controls of Q-factor within a frame, frame rate and color depth is introduced to maintain the required QOS, particularly the end-to-end throughput. The increases of the required bandwidth by redundant packet addition with FEC can be suppressed by the transcoding functions while the packet error rate is reduced to the accepted value. In order to verify the functionality and the efficiency in our suggested system, numerical simulation was held. As the result, our suggested system by combination of transcoding and FEC could correct the packet error rate with an order of 10⁹ while maintaining the frame rate and the amount of data transform at a constant.