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Object-based coding can potentially achieve a higher degree of compression and better visual quality. The objects in a scene are not always synchronous, that is, they have different temporal resolutions. In some applications, it is more efficient to transmit asynchronous objects with different temporal rates so as to achieve a better tradeoff between temporal and spatial resolutions. This requires to balance the qualities of individual objects while ensuring an overall visual quality with a given bit rate. This paper proposes a rate control algorithm for multiple video object encoding, which is suitable for both synchronous and asynchronous transmissions. The algorithm aims to maximize scene quality with an accurate bit rate, while efficiently handling buffer fullness. Using an efficient bit allocation strategy, the algorithm achieves accurate target bit rates, provides good coding quality, and decreases buffer overflow/underflow. The proposed algorithm also allows flexible priority adjustment among multiple objects to ensure overall better visual perception. Designed primarily for asynchronous objects, the algorithm treats the synchronous objects as a special case. Experimental results demonstrate that, when giving suitable asynchronous video object planes rates, the proposed algorithm achieves good temporal-spatial tradeoff while yielding accurate rate regulation and effective buffer control.