網路與多媒體技術的蓬勃發展促成了多樣化的多媒體應用，在不 同應用與網路資源下，我們希望壓縮後的視訊資料能符合頻寬限制與 使用者需求，並達到較好的影像品質。因此，當網路頻寬有限或受外 在環境改變影響時，視訊編碼器的位元率控制機制與其效能在視訊傳 輸上扮演著關鍵性的角色。 本論文於既有的H.264參考軟體JM 位元 率控制機制上，分別針對目標緩衝區與目標位元率的配置，提出符合 網路實際狀態的調整機制。首先在目標緩衝區的配置上，有別於JM使 用線性遞減的方式，本文藉由剩餘位元數的比率，動態地調整以符合 實際緩衝區滿溢程度的變化。此外，在目標位元率的配置上，有別於 JM使用平均位元率的方式，本論文根據實際可用位元率與預估可用位 元率的比較來配置位元率，以反映實際位元率與緩衝區流量的變化。 與JM15.1版本的模擬實驗比較，所提出的方式，不僅更能符合目 標位元率的要求、維持穩定的影像品質，同時也能夠減緩虛擬緩衝區 的負載程度，進而降低產生緩衝區溢位與緩衝區缺空的機率，使其穩 定地傳輸，有利於傳輸通道頻寬的改變。 ;The development of networks and video coding techniques promote the applications of multimedia communication. The objective of the service of multimedia applications is not only to deliver videos with better quality but also to maintain the compressed bit stream to meet the requirements under various network situations. Therefore, the rate control mechanism plays an important role in a practical encoding system.
The proposed methods can reflect the real status by utilizing the target buffer level and the target bits allocation. First, on the allocation of target buffer level, by using the ratio of remaining bits rather than linear decrease from JM, the proposed method can adjust dynamically to meet the actual buffer fullness. And then, on the allocation of target bits, by using the comparison of the actual available bit rate and the expected available bit rate rather than the average bit rate from JM, the proposed method allocates more suitable number of bits to reflect the actual bit rate and buffer fullness.
The experiment results are compared with JM 15.1 reference software. It shows that the proposed methods fit the target rate more accurately, get more stable video quality, and reduce the occupancy of the virtual buffer to avoid buffer overflow or underflow problems.
