Research And Implementation Of Video Error Resilience Based On Feedback Channel

With the development of human's living level, the demand for digital video communication such as video conferencing, video e-mailing and video telephonv has increased considerably so that these digital signal should be transmitted over the public switched telephone networks(PSTN) or wireless networks. When using these svstems, people hope the applications have relatively high reliability and small delays. But, transmission rates over PSTN and wireless networks are still limited. Futhermore, PSTN and wireless networks are error prone environment. Thus, a certain method's compression performance and channel error robustness level should be achieved with efficient source compression and error resilience.Ali current video coding standards such as H.263+ employ variable length codes(VLC), to achieve high compression efficiency. However, in an error prone environment, bit error(the worst: packet losses) may lead to the loss of synchronization at the receiver which can in turn lead to the loss of many video blocks and possibly frames. So error data causes spatial error propagation. Moreover, we use prediction coding process to achieve high compression efficiency, error data still cause errors to propagate in the temporal direction. So video optimized error resilience techniques are necessary due to the nature of video codec.This thesis first narrate H.263+ encode/decode structure,then briefly teli of the progress of error resilience. At last three techniques of error resilience are presented that are suited for real-time implementation in error-prone evnironrnents and their simulation results are showed. The first technique is error conceahnent. It is simple, but effectively elevate frame's quality subjectively. The second technique is error tracking. It is implemented at the encoder. It can terminated the error-progagation affects by INTRA refreshing the affected macroblocks. Its low memory requirement and flexible algorithms in complexity are particularly suitedfor real-time implementation. The third technique is odd and even packetization suited for real-time implement in Internet. If odd and even packetization technique cooperate with error concealment and error tracking ,the video will achieve good vision quality.