In order to provide good QoS for video streaming in error-prone environments, effective error control methods are essential. Current error control methods can be classified into two categories: 1) Transport layer approaches such as FEC and retransmission; 2) Application layer approaches such as error resilience coding and error concealment. By far, most existing research is aimed towards optimizing one of the above approaches to reduce the impact of transmission errors. However, there is usually more than one error control method in a real video streaming system. In this case, how to optimize the system performance becomes more complicated, and is not standardized. This paper presents the research effort to joint-optimize the effects of two error control methods, retransmission and error concealment, in wavelet-based video streaming system. The major difficulty of the joint-optimization is that the two methods are mutually dependent; the system cannot be optimized by improving each error control method independently. To tackle this problem, a new content index, namely "reconstruction distortion", is defined to quantify both the packet content and its importance in error concealment. Based on the defined content index, a content-based retransmission approach is developed to select the best packet-sending scheme to maximize the quality of the received video under the given error concealment method. Experiments results demonstrate the effectiveness of the proposed method.