Abstract: A new rate control scheme in H. 264 coding standard was proposed. The scheme includes+shape MAD prediction model based on space and time relativity of MAl).We used former frame bit usage as penalty factor to modify the bit allocation rule to balance buffer share. Furthermore,combining video text extraction technictues,the method realined macro bit allocation and quantization step based on text area. Experimental results show that the new ratccontrol scheme can control the bits very well and the average PSNR is improved.

Key words: H. 264,Rate control, Text object