在網際網路上傳送MPEG-4即時視訊，因為其具有即時性的限制及網路頻寬的變動而有封包延遲和遺失的情形。為了避免點對點之間封包大量的遺失和過度的延遲，除了利用TCP友好協定（TFRC）來傳送視訊串流外，編碼器的速率控制在MPEG-4視訊編碼標準及應用程式也扮演著重要的角色。在MPEG-4標準裡定義了相關的速率控制，其藉由改變影像的量化參數和允許略過不定數目的影像來滿足預期的位元率（bit rate）。然而，I frame的資料量太大導致突然的緩衝區激增可能會造成連續相鄰的影像被略過，而使得播放的品質降低。而且，調整TFRC傳送速率時，其振盪會過於劇烈而不適合MPEG-4編碼器。在這篇論文，我們提出一個具適應性的速率分配機制演算法，透過動態地調整I frame的資料量來降低連續相鄰的影像被略過。而對於TFRC速率的劇烈振盪，我們設計了一個指定速率平順演算法來將原本的速率平順化。實驗結果顯示出針對I frame的適應性速率分配可以有效地降低影像的略過並且改善了在時間上播放的品質。

　　Delivering MPEG-4 real-time video over the Internet has delay and loss requirements due to its timing constraint and bandwidth variation. To avoid the end-to-end bursty loss and excessive delay, TCP-friendly rate control (TFRC) protocol to transport video stream may be considered and the rate control of encoder thus plays an important role in MPEG-4 video-coding standards and applications. In the MPEG-4 standard, the corresponding rate control algorithm has been defined to satisfy the desired bit rate by changing quantization parameters of frames and allowing variable frame-skip. However, the instant buffer-level surge resulting from the great data rate of I-frames may make contiguous frame skipping, which will degrade the temporal quality. In addition, the adjustment of TFRC transmission rate may oscillate too violently to be suit for the encoder. In this paper, we propose an adaptive rate allocation algorithm to reduce the contiguous frame skipping by dynamically adjusting the data rate of I-frame. For the violent oscillation of TFRC transmission rate, we design a specified rate smooth algorithm smooth the original rate. Experimental results show that the adaptive rate allocation for I-frames effectively reduce the frame skipping and improve the temporal quality.

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