当H.263编码视频流在Internet上传输时，很容易受到信道错误的影响而丢失数据，由于数据的丢失不但会影响当前帧，还会连续传递到以后的解码帧，而导致图象质量的严重恶化，因此必须采用一定的措施来消除这种影响。目前较常用的错误掩盖算法是时域掩盖算法，而时域掩盖算法是利用参考帧来恢复当前帧损坏的图象数据，其计算较复杂，为此，提出了一种基于块匹配原则的时域掩盖算法，同时用三步搜索代替完全搜索来降低算法的计算复杂性，模拟结果显示，该算法由于能够在很短的处理时间内，获得较好质量的图象，因此能适应于视频会议等实时应用的要求。

When the compressed bitstream generated by a H.263 video coder is transmitted over the Internet, it is sensitive to packet loss. Due to the coding structure of the H.263 video compression algorithm, the packet loss can effect not only the current picture frame but also successive frame so that the quality of the video will be degraded seriously. The error concealment can be used to eliminate the effect. It commonly includes two methods : spatial concealment and temporal concealment. Spatial concealment uses the nearby correct image data of the corrupted part to recovery the image quality.The latter depends on the image data of the previous frame to estimate the lost data.However, spatial concealment will cause the blur of image quality and simple temporal concealment will make obvious artifacts. In this paper, we propose a temporal concealment algorithm based on block match principle. And in order to reduce the computational complexity, a new three step search algorithm is substituted for the exhaust search. Simulation results show that the proposed algorithm can produce acceptable quality of picture and can be implemented in the video conference application.