Recently, terrestrial stereoscopic 3DTV broadcasting services are under preparation. In order to support backward compatibility for the current 2DTV services with MPEG-2 video, one way for the new terrestrial stereoscopic 3DTV broadcasting services is to adopt a hybrid video codec system in which the current MPEG-2 standard is used for the left or right channel while a more efficient video codec is used for the other channel of a stereoscopic video. In this case, it becomes important to maintain the similar visual quality for output bitstreams given target bitrates. In this paper, a hybrid-codec based joint bit rate control scheme is proposed for stereoscopic video encoding, which is based on an optimization framework. The experimental results show that our proposed joint rate control scheme can effectively maintain similar visual qualities of the left-channel bitstreams by MPEG-2 and the right-channel bitstreams by H.264/AVC under target bitrate constraints.