Efficient two-ass rate control scheme based on adjusting distribution of discrete cosine transform coefficients

Video compression systems use rate control (RC) to achieve high visual quality under the constraint of a target bitrate. This work develops a two-pass variable bit rate (VBR) coding algorithm based on a group-of-picture (GOP) level ??-domain model. The discrete cosine transform (DCT) coefficients distribution that is generated in the first pass is modified to select an appropriate quantisation parameter (QP) that is used in the second pass, according to the target bit budget of GOP. Besides, the other important parameters, such as the header bits, are also predicted in the second pass to improve the RC ability. If a scene change happens in the first pass coding, the QP value will be adjusted in the second pass coding. Then, the QP is refined based on the textural complexity of every macroblock (MB). Experimental results demonstrate that the proposed VBR methods can not only achieve excellent visual quality but also reduce the variation in distortion even if a scene change happens.