在MPEG-2和H.264兩種視訊壓縮標準皆有採用可變長度解碼以移除統計上的冗餘進而達到資料壓縮，然而字元(codeword)採用可變長度的方式雖可達到資料壓縮，但過度的簡化亦可能影響解碼速度，故如何於解碼器中有效的存放字元是個相當重要的。此外這兩種視訊解碼規格，彼此存在著架構上的差異，因此本論文主要研究方向是支援MPEG-2以及H.264/AVC兩種視訊標準解碼，同時降低存放字元資料量以達到降低成本之目的，並考量解碼速度以符合即時播放的需求。
本論文提出兩種演算法來壓縮字元，第一個部份將字元表(codeword table)以二維樹狀結構表示，之後將二維樹狀結構轉為一維，此演算法雖可大幅度降字元個數，但解碼速度亦會受限於樹狀結構而無法做有效的提升，有鑑於此，本論文第二部份則是將樹狀結構做切割，利用附屬樹分類(sub-tree classification)的方式，相較於先期提出之樹狀結構壓縮演算法能進一步降低字元個數，在解碼速度上亦有大幅提升。本論文所提出之兩種演算法皆適用於MPEG-2和H.264兩種壓縮標準，故除字元資料儲存外，其餘的運算電路皆可重複利用故可有效降低硬體面積，由實驗結果可以得知，所提出來的MPEG-2/H.264架構，比起單獨的H.264與MPEG-2解碼器合起來的結果，可降低18%的硬體面積，而解碼速度亦符合即時播放之標準。

Most video compression standards, such as MPEG-2 and H.264/AVC, use variable length coding to remove statistical redundancy. Since the codewords are variable length, how to represent the codeword table to reduce the size of storage is quite important. However, the throughput of decoding may be suffered from codeword reduction. Besides, both MPEG-2 and H.264/AVC VLC decoder can not be combined directly due to the difference of codeword table of the two standards. In this thesis, we proposed a low-cost VLC decoder which supports MPEG-2 and H.264/AVC and achieves real-time decoding.
In this thesis, we first proposed a 2-D to 1-D tree translation scheme to minimize the number of stored bits. However, the throughput is also limited by the tree search decoding flow. Then we decomposed the VLC tree by use tree partition with sub-tree classification. Tree partition with sub-tree classification not only reduces the size of codeword storage but also improve the throughput compared to the proposed 2-D to 1-D tree translation scheme. The proposed method can support MPEG-2 and H.264/AVC decoding and has 20% of area reduced compared to the combination of H.264 decoder and MPEG-2 decoder. The throughput of the proposed design also meets real-timely video decoding.

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