隨著網際網路的發展，視訊通訊成為了人們生活當中不可或缺的一部份。一般人可以利用個人電腦、數位電視甚至行動電話等裝置透過有線或無線網路來收看各種節目。而由ITU-T所制定的H.264/AVC (以下簡稱 H.264) 正是一種適合視訊通訊的新編碼技術，因為H.264在同樣的影像品質下具有較高的壓縮比。
然而在網路環境下，尤其是在無線網路的環境裡，傳輸上的錯誤是無可避免的，封包遺失或者位元錯誤都是常常會發生的情況。因為視訊是必須是即時播放的，當錯誤發生時我們無法要求傳輸端重傳封包。因此，我們必須在接收端 (解碼端) 把這些錯誤隱匿起來。 H.264處理此類問題時是採用編碼端的錯誤回復(error resilience) 工具及解碼端的錯誤隱匿 (error concealment) 演算法，藉由上述機制讓接收端可以有效的利用正確接收之區域來重建接收錯誤之區域。在本文中，主要討論方向為解碼端之錯誤隱匿方法。
在H.264的標準當中雖然有錯誤隱匿的做法，但此一做法的整體表現還有很多可以改善的空間。在本文中，我們將提出一個改良的錯誤隱匿方法。在I-frame中，我們改進了內插法的方法並且利用資料隱藏的技巧來提升整體效能。而在P-frame中，我們將“Temporal Error Concealment” (TEC) 及 “Spatial Error Concealment” (SEC)加以混用，使得我們在I-frame上的改良方法也可以加以運用在P-frame上。實驗結果顯示，不論是在人眼視覺系統上或是在PSNR上，我們所提出的方法都可以達到一定程度的改善，因此這樣的方法是適合運用於無線網路下的H.264視訊通訊。

With the development of internet, video communication becomes an important application in human’s life. People can use PC, DTV, and even mobile phone to watch video programs over IP or wireless network. H.264/AVC (called H.264 as well) is a new standard made by ITU-T with high entropy rate and its bit stream is very suitable for video communication.
However, in a network, especially in a wireless network, transmission error is inevitable so that packet loss and bit error occur very often. It is impossible to ask the sender to resend packets in the video communication’s environment because the video sequence should be played in real time. At such situation, we have to adapt a method to conceal those errors in decoder instead of asking sender to resend packets. H.264 handles this problem by taking use of error resilience tools on encoder and error concealment algorithms on decoder so that the receiver can use correct regions to reconstruct the lost regions. The main topic to be discussed in this paper is error concealment on the decoder side.
There is a default error concealment algorithm in H.264 standard, but the performance is not so good. In this paper, we will propose a refined error concealment algorithm. In I-frame, we improved the interpolation algorithm and use data hiding technique in some condition to make the performance be better. And in P-frame, we hybrid “Temporal Error Concealment” (TEC) and “Spatial Error Concealment” (SEC) to introduce our proposed method in I-frame into P-frame. The experience results show that our method can enhance the performance on both human vision system and PSNR. Our proposed method is suitable for the error concealment in H.246 video communication over wireless network.

[1] D. Agrafiotis, D. R. Bull, C. N. Canagarajah, “Enhanced Error Concealment With Mode Selection,” IEEE Trans. on Circuits and Systems for Video Technology , vol. 16, no. 8, pp. 960 – 973, 2006.
[2] X. Xiu, L. Zhuo, L. Shen, “A hybrid error concealment method based on H.264 standard,” procceding of ICOSP, vol. 2, pp. 16-20, 2006.
[3] M. J. Chen, W. W. Liao, M. C. Chi, ”Robust temporal error concealment for H.264 video decoder,” proceedings of ICCE, pp. 383 – 384, 2006.
[4] K. Donghyung, Y. Siyoung, J. Jechang, “A new temporal error concealment method for H.264 using adaptive block sizes”, procceding of ICIP, vol. 3, no.3, pp. 928-931, 2005.
[5] W. K. Li, J. L. Jin, ”An error resilient coding scheme for H.264 video transmission based on data embedding” , procceding of ICASSP, vol. 3, no. 3, pp. 257-260, 2004.
[6] Y. L. Xu, Y. H. Zhou, “H.264 video communication based refined error concealment schemes” , IEEE Trans. on Consumer Electronics , vol. 50, no. 4, pp. 1135 – 1141, 2004
[7] Y. L. Xu, Y. H. Zhou, “Refined video error concealment over wireless IP network” , proceedings of the IEEE 6th Circuits and Systems Symposium, vol. 1, pp. 257 – 260, 2004
[8] S. Wenger, “H.264 over IP,” IEEE Trans. on Circuits and Systems for Video Technology, ,vol. 13, no. 7, pp. 645- 656, 2003
[9] T. Wiegand, G. J. Sullivan, G. Bjntegaard, A. Luthra, “Overview of the H.264 video coding standard,” IEEE Trans. on Circuits and Systems for Video Technology, vol. 13, no. 7, pp. 560- 576, 2003.