視訊於網路傳輸時，常會發生網路封包遺失的情況，視訊解碼器無法正常解碼，因此造成令人不悅的視訊品質。新一代H.264視訊壓縮編碼雖具有高壓縮效能，卻也導致了發生錯誤時較為嚴重的錯誤蔓延，造成視訊品質的劇烈降低，因此發展視訊傳輸之錯誤保護機制是非常重要的。 系統失真式錯誤保護(Systematic Lossy Error Protection；SLEP)機制是一種可有效對抗視訊傳輸錯誤的方法，此架構利用Wyner-Ziv編碼方式保護視訊，在錯誤率提升時，不至於發生一般錯誤更正碼(FEC)保護方式所導致的嚴重視訊品質急速降低，可提供較平穩的視訊品質。本論文在H.264上實作並研究SLEP機制，以此架構為基礎，在SLEP的抗錯能力與解碼視訊品質之間做最佳取捨，採用各種不同編碼方式產生冗餘切片，希望找出最合適的冗餘切片編碼方式，最後並根據分析結論，提出適應性的錯誤保護方式，望能進一步提升SLEP的抗錯效能。 如我們所預期的，SLEP機制在網路封包遺失率逐漸增高時，達成了平穩的視訊品質降落，並提供可接受的視訊品質。 There are inevitable packet losses when the video transmits over the network, and that leads to the video decoder can’t decode correctly, hence results in unpleasant video quality. The new generation of H.264 video compression standard exhibits high compression efficiency, but occasionally incurs more serious error propagation when an error occurs and this makes the video quality degrade drastically. Therefore, the development of an effective error protection mechanism for the video transmission is very important. Systematic Lossy Error Protection (SLEP) is a robust error resilient mechanism which uses Wyner-Ziv coding to protect the video bitstream. SLEP avoids the “cliff” effect, i.e., the rapid degradation of video quality when too many packets are lost and the FEC code fails to recover them, from which the FEC system suffers and produces graceful degradation of the decoded video quality with the increase of error probability. In this thesis, we study and implement the SLEP architecture on H.264 and try to get the best trade-off between the error resilience and decoded video quality. We propose an adaptive SLEP structure for further improvement of error resilience capability by generating redundant slices with different coding methods for different channel conditions. As expected, the SLEP architecture achieves graceful degradation of video quality and provides acceptable visual quality in the presence of increasing network packet losses.
