The object based rate control problem arises along with the video object concept proposed by MPEG 4. The video objects can be coded in synchronous or asynchronous way

but latter one has more advantages in low bit rate coding and it is also proved by the experiments of this paper. This paper proposes a new rate control algorithm which can achieve a constant bit rate when coding asynchronous video objects. Firstly

the algorithm estimates the total target bits at one time assuming that the video plane from the same video objects of the same coding type and close in time are coded with a similar number of bits. Then the algorithm to allocate the target bits to the coding video objects at the time in order to achieve constant distortion ratios between pairs of video object planes adopts an allocation policy called constant distortion ratios. This paper also proposes a post processing technology to solve the problems of composition picture quality brought by asynchronous video objects. The experimental results show that the algorithm can efficiently control the coding bits of asynchronous video objects and achieve high subject and object quality.